Publikace katedry

Autoři:

Ing. Veronika Drechslerová; Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2024, Vol. 48 (2024): 19th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), ISBN 978-80-01-07358-2

Anotace:

The paper deals with the examination of the ageing effects on the mechanical properties stability of 3D printed material via stereolithography under compression when subjected to various conditions, including UV radiation, X-rays, and the effects of time, from the opening of the bottle with the material to the 3D-printing process. The sets of samples under investigation were subjected to quasi-static and dynamic compression loading using an Split Hopkinson Pressure Bar. The aim of this paper is to investigate the long-term stability of the samples in terms of their mechanical properties and material behaviour and their degradation pattern. Despite the manufacturer’s information, it was found that the mechanical behaviour of the printed samples was significantly affected by the ageing process.

DOI:

10.14311/APP.2024.48.0015

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Dr. Afdhal Afdhal; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Dwianto, Y.B.; Palar, P.-S.

Publikováno:

2024, Materials & Design, 244, p. 1-13), ISSN 1873-4197

Anotace:

In this paper, a set of hexachiral auxetic structural designs with near zero Poisson's ratio (ZPR) characteristics is discovered via the combination of machine learning and experimentally validated finite element simulation. An active learning-enhanced Gaussian process model is utilized to generate multiple designs with near-ZPR properties and discover the boundary of the positive and negative Poisson's ratio. The results show that active learning successfully constructs a probabilistic estimation of the ZPR boundary. A comprehensive analysis of the identified ZPR contour is performed to extract crucial design insights. The findings indicate that the near-ZPR characteristic can be attained through various combinations of geometric parameters. This offers users the flexibility to select the configuration that best aligns with their specific requirements. Additionally, an investigation of the various ZPR configurations that have been discovered is carried out to understand the mechanism that yields near-ZPR property. One discovered near-ZPR design was subsequently fabricated using 3D printing for validation purposes. The experimental outcomes demonstrated a good agreement with the numerical predictions, underscoring the effectiveness of the active learning strategy in uncovering designs that closely approach ZPR conditions.

DOI:

10.1016/j.matdes.2024.113133

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Hurtig, K.

Publikováno:

2024, Transforming Construction: Advances in Fiber Reinforced Concrete, Springer Nature), p. 573-580), ISBN 978-3-031-70144-3, ISSN 2211-0844

Anotace:

he Ultra high-performance steel fibres reinforced concrete (UHPFRC) investigated in this paper is a fine-grained cement-based composite material with outstanding mechanical properties. Its key attributes include an ultra-high compressive strength in excess 150 MPa and a permanent post-cracking strength in excess 5 MPa. To increase its structural integrity, steel fibres 13 mm long and 0.2 mm in diameter are added to the matrix to reinforce it. In order to assess the properties of the UHPFRC under varying loading conditions, the prism-shaped specimens are subjected to three-point bending tests over a range of loading rates from quasi-static regime to dynamic impacts at intermediate strain rates. The experiments are performed using an in-house developed testing machine based on linear motors and are conducted at 4 different loading velocities with at least 5 specimens tested at each strain rate. The tests are observed using a high-speed camera. For a better understanding of the material behaviour, the testing equipment is combined with a laboratory high power X-ray imaging set-up that allows internal inspection of the samples to analyze the effect of imperfections, inhomogeneities, voids and dominant fibre orientation. X-ray imaging is performed before and after mechanical testing and also in-situ during the loading using a high-speed X-ray imaging camera. A significant dynamic increase factor is observed between the individual strain rates, while the dominant fibre orientation is identified as a crucial aspect causing the differences between the specimens. This innovative experimental approach provides invaluable insights into the material response to dynamic loading conditions and offers a comprehensive understanding that is crucial for optimizing its performance in a variety of real-world applications.

DOI:

10.1007/978-3-031-70145-0_69

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Mauko, A.; Emre Yilmaz, Y.; Novak, N.; Ing. Tomáš Doktor, Ph.D.; Vesenjak, M.; Ren, Z.

Publikováno:

2024, Composite Structures, 333, p. 1-10), ISSN 0263-8223

Anotace:

The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials.

DOI:

10.1016/j.compstruct.2024.117949

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Duarte, I.

Publikováno:

2024, Materials Letters, 2024 (354), p. 1-4), ISSN 0167-577X

Anotace:

Processes of internal damage development during localized dynamic penetration represent a crucial mechanism important for relevant analysis of deformation and failure of plates and sandwich panels under high strain rate conditions. Soft cellular materials are of special importance as the internal damage defines mode of collapse and energy absorption capabilities. In this paper, a fast X-ray radiography is employed for in-situ analysis of the internal damage development in soft closed-cell aluminum foam subjected to a localized high strain rate penetration using an instrumented projectile in a direct impact Hopkinson bar apparatus. The process with a typical duration of a few milliseconds is visualized using four X-ray projections acquired using a flash X-ray system and a high-speed camera. Internal damage such as cracking, shear failure in the vicinity of the projectile, and compaction of the material is successfully identified. This unique method utilizing a laboratory based X-ray source allows for characterization of the penetration mechanism that has been usually analyzed only in post-mortem state.

DOI:

10.1016/j.matlet.2023.135372

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. et Ing. Radim Dvořák; González, J.A.

Publikováno:

2024, Computer Methods in Applied Mechanics and Engineering, 432 (Part A), ISSN 1879-2138

Anotace:

We propose a novel optimization technique for the automatic construction of interface operators for coupling non-matching 3D meshes. The core of the method lies in the use of localized Lagrange multipliers and least-squares approximation to find the optimal location of additional interface nodes, allowing the problem to be solved without modifying the meshes of the coupled subdomains and passing the patch test. Although many techniques exist in the literature for coupling incompatible meshes, such as the widely accepted Mortar method, which solves the problem exactly, the proposed method brings two crucial advantages: first, it eliminates the need to compute complex surface integrals on the intersection of the boundary meshes (thanks to the use of techniques adapted from the existing method of localized Lagrange multipliers); and second, and more importantly, we achieve this passing the patch test with comparable accuracy to Mortar. The efficiency and accuracy of the proposed coupling technique is demonstrated by comparing its results with other coupling methods and by solving various theoretical and practical examples with exact and experimental solutions in statics and dynamics.

DOI:

10.1016/j.cma.2024.117336

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Čítek, D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2024, Emergent Materials, 2024, ISSN 2522-5731

Anotace:

Excellent mechanical properties of ultra high performance concrete make it suitable for use in special applications, where the material is subjected to dynamic phenomena such as impacts, explosions, or earthquakes. This paper presents a novel experimental approach that integrates a Split Hopkinson Pressure Bar with a flash X-ray system and high-speed optical imaging to investigate the dynamic behavior of steel fiber reinforced UHPC under high strain rate uni-axial compression. In-situ Flash X-ray radiography emerges as a particularly effective tool, providing clear visualization of deformation response and overcoming challenges associated with flying debris encountered in optical inspection. Moreover, computed tomography and scanning electron microscopy appear as a vital technique for analyzing micro-structure and fiber distribution and orientation. The combined approach offers a promising method to study the dynamic behavior of steel fiber reinforced ultra high performance concrete and also holds promise for analyzing more complex modes of deformation and material interactions, providing valuable insights for enhancing the design and performance of critical infrastructure subjected to dynamic loading events.

DOI:

10.1007/s42247-024-00893-w

Typ:

Článek v periodiku excerpovaném databází Scopus

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Jan Falta; Ing. Michaela Jurko

Publikováno:

2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 6-11), ISBN 978-80-01-07237-0, ISSN 2336-5382

Anotace:

This contribution deals with an asynchronous direct time integration of the finite-element model. The proposed method is applied to the phenomenon of wave propagation through an elastic linear continuum. The numerical model is partitioned into individual subdomains using the domain decomposition method by means of localized Lagrange multipliers. For each subdomain, different time discretizations are used. No restrictions for relation between subdomain’s time steps are imposed. The coupling of the subdomains is forced by an acceleration continuity condition. Additionally, we use the a posteriori technique to also provide the displacement and velocity continuity at the interfaces, and hence we obtain exact continuity of all three kinematic fields. The proposed method is experimentally validated using the modified SHPB (split Hopkinson pressure bar) setup.

DOI:

10.14311/APP.2023.42.0006

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; González, J.A.; Park, K.C.

Publikováno:

2023, Proceedings of the 9 th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Athens, Institute of Structural Analysis and Antiseismic Research, NTUA)

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Dr. Afdhal Afdhal; prof. Ing. Ondřej Jiroušek, Ph.D.; Palar, P.S.; Ing. Jan Falta; Dwianto, Y.B.

Publikováno:

2023, Materials & Design, 232, p. 1-13), ISSN 1873-4197

Anotace:

A design exploration of hexachiral structures using explainable machine learning (ML) is performed in this work. The hexachiral structures are fabricated using resin via vat photopolymerization (VPP). The ML model is used to build the function that explains the association between Poisson’s ratio and the hexachiral design parameters. The data set for ML model construction is first collected by using the Halton sequence and simulated using the finite element method (FEM). To validate the data set, the results obtained from the FEM simulation are compared with those obtained from the compression test. The Gaussian Process Regression (GPR) models for Poisson’s ratio and porosity are constructed to extract important design insight. A Global Sensitivity Analysis (GSA) and Shapley Additive Explanations (SHAP) are used to analyze the sensitivity of the porosity and Poisson’s ratio to the hexachiral design parameters. GSA result shows that the strut’s thickness is the most decisive parameter that affects the Poisson’s ratio. The application of SHAP also reveals that the relationship between the strut thickness and Poisson’s ratio is nonlinear. Finally, the minimum Poisson’s ratio value is achieved by design with minimum strut thickness, minimum node radius, and maximum strut length.

DOI:

10.1016/j.matdes.2023.112128

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Veronika Drechslerová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Ing. et Ing. Radim Dvořák; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 1-5), ISBN 978-80-01-07237-0, ISSN 2336-5382

Anotace:

This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on the mechanical properties of the material and printed samples. The aging of the material could be a problem for its subsequent use as the stability of the mechanical properties would not be maintained and unwanted deterioration of the material could occur. As part of the research, sets of samples were printed and subjected to different aging methods and subsequently subjected to quasi-static and dynamic uni-axial load tests. From the data obtained, the basic mechanical properties of the material were calculated and compared with each other. The aim of this paper was to investigate whether aging process causes significant changes in the mechanical properties of the materials used, which could have a consequential impact on their use in different industries.

DOI:

10.14311/APP.2023.42.0001

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Bc. Blanka Žaloudková; Sekorová, Š.; Kopecká, B.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 94-97), ISBN 978-80-01-07237-0, ISSN 2336-5382

Anotace:

Long-term stability of the tissue product in terms of mechanical parameters is a key factor for its expiration date. For the investigation of storage effects on the cartilage tissues the experimental mechanical loading test combined with XCT scanning for the irregular shape inspection was performed. The samples were preserved according to three different protocols using the deep-freezing and two types of saline solution preservation. The stability of the biomechanical parameters was tested within annual intervals. All samples were subjected to uni-axial compression loading using the in-house developed compact table top loading device in displacement-driven mode. Based on the measurements, the results are represented in the form of stress-strain curves and quantified as elastic modulus and ultimate compression stress. It can be concluded that no significant difference was found in neither the mechanical properties of the samples nor in the effects of each preservational method.

DOI:

10.14311/APP.2023.42.0094

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Mračko, M.; Ing. Ján Kopačka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Ing. Michaela Jurko; Ing. Václav Rada

Publikováno:

2023, Computer Methods in Applied Mechanics and Engineering, 413, p. 1-26), ISSN 1879-2138

Anotace:

The derivation and implementation of an asynchronous direct time integration scheme for domain-decomposed finite element models is presented. To maximize clarity in the description of the proposed asynchronous integration, the scheme is restricted to the linear-elastic stress wave propagation case. The proposed method allows the integration of individual subdomains with independent time steps. There is no requirement for an integer time steps ratio of the interacting domains while maintaining zero interface energy. The subdomains are connected by the condition of the continuity of the acceleration field at the interface. In addition, the a posteriori technique is applied to satisfy the continuity of the displacement and velocity fields. Another important contribution of this paper lies in the description of the implementation — we offer the reader a general description of the implementation of the case of any number of subdomains with any number of constraints between them, while the basics of the algorithm are explained on a single domain pair. The functionality of the asynchronous integrator is verified by solving selected problems and comparing with analytical solutions and experimental measurements obtained using a Split Hopkinson pressure bar setup. © 2023 Elsevier B.V.

DOI:

10.1016/j.cma.2023.116110

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Zeman, L.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Nela Krčmářová; Koudelková, V.; Zeman, J.

Publikováno:

2023, Young Transportation Engineers Conference 2022, Praha, České vysoké učení technické v Praze), p. 89-97), ISBN 978-80-01-07224-0, ISSN 2336-5382

Anotace:

The article presents a study of the mechanical processes occurring during the aluminothermic reaction using experimental methods (strain gauges, digital image correlation, thermography, scanning electron microscopy, profilometry). The aluminothermic reaction is a highly efficient welding method due to its exothermic behaviour, however, it places considerable demands not only on the welding technique, but also on the capabilities of the experimental methods used; these limitations are also discussed in the article. The aluminothermic reaction is associated with the formation of a localised heat source with a time evolution dictated by the technological procedure, which manifests itself in heat propagation to the surrounding weld material. The unequal evolution of the temperature field is the fundamental cause of the appearance of the heat affected zone or local deformations or surface curvature, which was the focus of the experimental methods deployed above and the results of which are shown in the article.

DOI:

10.14311/APP.2023.41.0089

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.

Publikováno:

2023, Wave Motion, 121, ISSN 0165-2125

Anotace:

This is a presentation of robust and accurate explicit time-stepping strategy for finite element modeling of elastic discontinuous wave propagation in strongly heterogeneous, multi-material and graded one-dimensional media. One of the major issues in FEM modeling is the existence of spurious numerical stress oscillations close to theoretical wave fronts due to temporal-spatial dispersion behavior of FE discretization. The numerical strategy presented for modeling of 1D discontinuous elastic waves is based on (a) pushforward-pullback local stepping — ensuring the elimination of dispersion due to different critical time step sizes of finite elements, (b) domain decomposition via localized Lagrange multipliers — to satisfy coupling kinematics and dynamic equations , (c) asynchronous time scheme — ensuring the correct information transfer of quantities for the case of integer ratios of time step size for all domain pairs. Dispersion behaviors, existence of spurious stress oscillations, and sensitivity of the dispersion to time step size are then suppressed. The proposed method is numerically tested with regard to the rectangular step pulse elastic propagation problem considering in-space varying Young’s modulus. To prove robustness and accuracy, a comparison with results from commercial software, an analytical solution, and experimental data from partial assembly of a split Hopkinson pressure bar (SHPB) setup is provided.

DOI:

10.1016/j.wavemoti.2023.103169

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 77-82), ISBN 978-80-01-07237-0, ISSN 2336-5382

Anotace:

X-ray radiography and computed tomography have become well-established methods for investigation of internal structure of objects and for defectoscopy. Recently, the methods have even been used for in-situ analysis of materials under mechanical loading. Although the techniques would be very suitable for analysis during dynamic events, their application is constrained by typical achievable frame rates. Therefore, fast imaging is usually limited to facilities providing sufficient flux like particle accelerators. In this paper, we test imaging performance of a laboratory-based setup with a high-power X-ray tube, a scintillation panel, and an optical camera. Fast-rotating object and typical specimens for impact testing are irradiated with different power settings and quality of captured images is evaluated and analyzed. It is found out that the system can be successfully used for imaging at several hundred frames per second allowing for inspection of slow impact dynamics experiments.

DOI:

10.14311/APP.2023.42.0077

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Michaela Jurko; Ing. Veronika Drechslerová; Ing. Petr Koudelka, Ph.D.; Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2023, Advanced Engineering Materials, 25 (24), ISSN 1527-2648

Anotace:

The paper deals with the dynamic penetration of 3D printed panels with auxetic and conventional honeycomb unit cell-based cores. The geometry of the unit cells and their periodic assembly in the resulting lattices were selected to ensure the same relative density and overall weight of the individual sample types. Such a similarity of both specimen types allowed the evaluation of differences between conventional and auxetic lattices in terms of penetration characteristics and deformation energy mitigation properties. Dynamic penetration of the samples was performed using a fully strain-gauge instrumented Open Hopkinson Pressure Bar (OHPB) at three impact velocities resulting in three loading scenarios. All performed experiments were captured by two optical cameras for detailed observation and for tracking of an impactor movement using Digital Image Correlation (DIC). The force-penetration depth relation was used to evaluate the elastic and post-yield compression characteristics of the lattices together with their deformation energy mitigation capabilities. The results show that the main differences in the deformation response of lattices consist of lower overall stiffness and effective yielding of the auxetic lattices at higher penetration depth. Numerical simulation using an explicit solver was performed to analyze the deformation mechanism of the individual core types.

DOI:

10.1002/adem.202300980

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Jan Falta; Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; Vavro, M.; Vavro, L.

Publikováno:

2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 17-21), ISBN 978-80-01-07237-0, ISSN 2336-5382

Anotace:

This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic conditions, while standard uni-axial loading device is used for evaluation in quasi-static conditions. Basalt specimens were subjected to four different loading-rates from 200-600 s−1 on which the stress-strain dependence was evaluated together with DIC analysis of crack initiation and disintegration process. Understanding the mechanical properties of basalt can provide insights for engineers and designers in creating structures that are durable and able to withstand different loading conditions. The findings of this study can have implications for a wide range of industries, including aerospace, automotive, and construction, among others.

DOI:

10.14311/APP.2023.42.0017

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Ing. Josef Svoboda; Ing. Přemysl Toman; Abraham, D.; Zeman, J.; Heřmanová, J.; Ing. Jan Vyčichl, Ph.D.; doc. Ing. Petr Bouchner, Ph.D.; Jan Válek, DiS.; Ing. Josef Mík, Ph.D.; Ing. Vojtěch Thums; Bc. Tomáš Kotvald; Derner, T.; Plášek, J.; Malec, Š.

Publikováno:

2023

Anotace:

In the scope of the Motostudent 2023/24 competition there was created complex project of the whole motorcycle in the category of Electro bikes. Report contains conceptual design, detailed design, prototyping and development.

Typ:

Oponovaná technická zpráva cizojazyčně

Autoři:

doc. Ing. Jitka Jírová, CSc.

Publikováno:

2023, ISBN 978-80-01-07257-8, ISSN 2336-5382

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Čítek, D.

Publikováno:

2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 51-54), ISBN 978-80-01-07237-0, ISSN 2336-5382

Anotace:

Ultra high performance concrete is a modern cementitious material which exhibits excellent mechanical properties such as damage tolerance, fracture toughness and durability. These features make this materials suitable for wide range of applications where is the material subjected to different modes of loading and different loading rates. This paper deals with measurement of the Ultra high performance concrete reinforced with steel fibres in quasi-static compression mode of deformation and two elevated strain rates using split Hopkinson pressure bar. The results of the measurement show high increase of the mechanical properties with elevated strain rate.

DOI:

10.14311/APP.2023.42.0051

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Veronika Drechslerová; Ing. Michaela Jurko; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; Ing. et Ing. Radim Dvořák

Publikováno:

2023, Inovace v aditivních technologiích INAM 2023, Jihlava, Vysoká škola polytechnická Jihlava), p. 13-13), ISBN 978-80-88064-66-4

Anotace:

Příspěvek je zaměřený na vhodnost využití stereolitografie (SLA) pro výrobu porézních struktur s potenciálem vysoké absorpce energie nárazu. SLA je technologií aditivní výroby využívající principu vytvrzování tekutých pryskyřic pomocí záření určité vlnové délky [I. Romero-Ocaña, S.I. Molina 2022]. Pro posouzení vlivu použitého materiálu na výsledné mechanické vlastnosti byly sady testovacích vzorků vyrobeny ze tří různých pryskyřic a následně vystaveny kvazi - statickým jednoosým tahovým a tlakovým zkouškám. Z naměřených dat byly vytvořeny diagramy napětí - deformace a spočítány základní materiálové vlastnosti. Na základě získaných poznatků bylo optimalizováno nastavení parametrů výrobního procesu pro zajištění požadované kvality tisku, odezvy 3D tištěných vzorků na zatěžování v závislosti na volbě použité pryskyřice a zhodnocena celková vhodnost metody SLA pro výrobu pokročilých celulárních struktur.

DOI:

10.14311/APP.2023.41.0001

Typ:

Abstrakt ve sborníku z lokální konf. česky

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; González, J.A.

Publikováno:

2023, Proceedings of the 1st Conference on INAM 2023, Jihlava, Vysoká škola polytechnická Jihlava)

Typ:

Abstrakt ve sborníku z lokální konf. česky

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2023, ISBN 978-80-01-07237-0, ISSN 2336-5382

Typ:

Sborník z mezinárodní konf. v češtině

Autoři:

Ing. Tomáš Fíla, Ph.D.

Publikováno:

2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 109-112), ISBN 978-80-86246-51-2, ISSN 1805-8256

Anotace:

Stress uniformity in a specimen represents a crucial parameter for validity of impact experiment conducted in a split Hopkinson bar. Principle of the experimental method is to measure elastic stress waves that propagate in the bars of an experimental setup and to calculate stress to strain relations at the interfaces with the specimen. However, standard procedure to evaluate the experiment can only be valid when stress is distributed approximately uniformly along the specimen. As the stress wave has to propagate through the specimen during the experiment, a time period of significantly non-uniform stress distribution is present and a certain number of wave transits is required to achieve approximately uniform stress distribution. In this paper, a simple analytical model assuming one-dimensional wave propagation theory, non-equal mechanical impedance of the bars and linear elastic material model of the specimen is introduced to determine a number of transits required to achieve uniform stress distribution in the specimen. Potential of the calculated results is discussed in an experiment using a direct impact Hopkinson bar and a material with significant plateau in its stress-strain response.

DOI:

10.21495/512109

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Novak, N.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Václav Rada; Ing. Tomáš Doktor, Ph.D.; Al-Ketan, O.; Rowshan, R.; Vesenjak, M.; Ren, Z.

Publikováno:

2022, Materials Science and Engineering A - Structural Materials: Properties, Microstructure and Processing, 852 (5), ISSN 0921-5093

Anotace:

One of the most promising options for future crashworthiness applications is thin-walled tubes filled with various cellular materials (e.g. metal foam). Of higher interest are the shell-based lattices, which have lately gained popularity due to their superior qualities over strut-based lattices. In this work, we investigate the mechanical response of foam-filled tubes where the tube's core was represented by Triply Periodic Minimal Surface (TPMS) diamond lattices. Samples made of stainless steel 316L comprising the diamond lattice core, empty tubes, and in-situ TPMS-filled tubes were additively manufactured and mechanically tested under compressive loading. As-fabricated welded tubes and ex-situ TPMS-filled tubes were also analysed and compared. Under the axial loading, the ex-situ and in-situ TPMS-filled tubes showed very similar behaviour. Enhanced energy absorption up to 21% and 44% compared to the sum of empty tubes and the core responses was noted. The energy absorption enhancement of 12% in the case of transversal loading is limited to in-situ TPMS-filled tubes, where the connection between the tube and core prevents the tube's walls from buckling. Computational models with homogenised core were developed and validated based on the experimental data. These straightforward, fast, and accurate computational models can be efficiently used for large-scale real-life applications, e.g. crash and impact.

DOI:

10.1016/j.msea.2022.143680

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; Ing. Václav Rada; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 107-107)

Anotace:

Additively manufactured materials represent an advanced type of engineering material allowing for rapid building of parts with complex design. Additively manufactured metallic materials are particularly promising for application in high-tech industry, requiring optimized parts with complex shape and high performance mechanical properties. In this contribution, the cylindrical specimens manufactured from 316L powdered stainless steel built in different orientations to the printing platform are subjected to compression at high strain rates using split Hopkinson pressure bar (SHPB). The specimens are subjected to quasi- static and dynamic compression at strain rates ranging from 1500/s to 5000/s. Changes in damage development and failure mode are investigated through combination of high speed optical imaging with data of the SHPB instrumentation. For the testing, the SHPB with high strength aluminum alloy bars, soft copper pulse shapers and two sizes of the striker bar is used. The bars are instrumented with a set of foil strain-gauges. The experiments are observed by stateof-the-art high speed camera with frame rate of approximately 250kfps. The camera is time synchronized with the data acquisition system. Strain localization and changes in failure mode related to the printing orientation and strain rate, particularly occurrence of the fatal macroscopic crack and identification of the corresponding failure strain, are investigated using digital image correlation (DIC). It is found out that the failure mode changes dramatically with the increasing strain rate resulting in sudden and complete failure of the specimen during high strain rate compression. The failure is dependent on both the printing orientation and the strain rate.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 85-88), ISBN 978-80-86246-51-2, ISSN 1805-8256

Anotace:

In this study, the relation between the presence of the filler in different types of open auxetic lattices and their Poisson’s functions was investigated using optical strain measurement technique and Digital Image Correlation (DIC) algorithms. Three different types of auxetics were manufactured using Selective Laser Sintering (SLS) technique from 316L–040 stainless steel alloy: (i) 2D re-entrant, (ii) 3D re-entrant and (iii) 2D missing rib structure. All types of SLS printed auxetics were then divided into three different groups according to the presence of the filler: (a) unfilled and filled with (b) porous polyurethane foam and (c) ordnance gelatin. All groups of sam- ples were tested in uniaxial compression mode under both quasi-static and high strain rates in the range of thousands strains per second using the Split Hopkinson pressure bar. During the loading tests, the deforming structure was observed optically and from the captured image data, the in-plane displacements were calculated using DIC. Based on these displacements, Poisson’s functions among the tested groups were compared. The results show that in the case of both types of polymeric fillers, the auxetic behaviour is suppressed with increasing values of longitudinal strain.

DOI:

10.21495/51285

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Gonzalez, J.A.; Park, K.C.

Publikováno:

2022, DD27 abstract book, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE)

Anotace:

The problem of the linear elastodynamics including domain decomposition via localized Lagrange multipliers method is solved using nite element method and direct time integration. Time integration of domains is performed separately with dierent time steps. The asynchronous integrator scheme is generalized for multiple domains problem and enhanced by the use of a local variant of the pushforward-pullback method, which eectively avoids spurious oscillation in steep stress pulses response. The proposed method is applied to the rectangular step pulse propagation problem considering the linearly varying Young modulus in space as well as the bi-material interface problem. To prove the robustness and the accuracy, the comparison with analytical solution and commercial soft- ware outputs is provided.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.

Publikováno:

2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems)

Anotace:

The problem of the linear elastodynamics including domain decomposition via localized Lagrange multipliers method [2] is solved using finite element method and direct time integration. Time integration of domains is performed separately with different time steps with integer ratio. The known asynchronous integrator scheme [1] is generalized for multiple domains problem and enhanced by the use of a local variant of the pushforward-pullback method, which effectively avoids spurious oscillation in steep stress pulses response. The proposed method is applied to the rectangular step pulse propagation problem considering the linearly varying Young modulus in space as well as the bi-material interface problem. To prove the robustness and the accuracy, the comparison with analytical solution and commercial software outputs is provided.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.

Publikováno:

2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 35-35)

Anotace:

The problem of the linear elastodynamics including domain decomposition via localized La- grange multipliers method [2] is solved using finite element method and direct time integration. Time integration of domains is performed separately with different time steps with integer ra- tio. The known asynchronous integrator scheme [1] is generalized for multiple domains prob- lem and enhanced by the use of a local variant of the pushforward-pullback method, which effectively avoids spurious oscillation in steep stress pulses response. The proposed method is applied to the rectangular step pulse propagation problem considering the linearly varying Young modulus in space as well as the bi-material interface problem. To prove the robustness and the accuracy, the comparison with analytical solution and commercial software outputs is provided.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Felten, M.; Fries, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.

Publikováno:

2022, Advanced Engineering Materials, 24 (3), ISSN 1438-1656

Anotace:

Open-cell metal foams are a versatile class of porous lightweight materials, which are predominantly used as kinetic energy absorbers in a wide scope of applications. Based on their bio-inspired inhomogeneous 3D porous structure, they are capable to significantly reduce the mass of structural designs. Starting with a polyurethane (PU) template foam, the specimens in the present contribution are manufactured by an electrochemical nickel (Ni) deposition. This manufacturing process is beneficial regarding both the specimen design and the adjustment of mechanical properties correlated with the Ni-coating thickness. Herein, the strain-rate sensitivity of open-cell Ni/PU hybrid metal foams is investigated by quasistatic compression tests and high-velocity impact tests conducted with a conventional split-Hopkinson pressure bar device.

DOI:

10.1002/adem.202100872

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Veronika Drechslerová; Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 104-104)

Anotace:

The mechanical response of sandwich panels tailored to specific applications investigated becomes an extensively topic for research teams. Sandwich panels typically consist of a lightweight core (porous materials, meta-materials structures) and covering shell (solid or composite layer). These materials can be used as, e.g., the main component of crumple zones in vehicles or low-velocity protection in many applications, due to their high specific energy absorption and low density. An unique loading mode in dynamic mechanical testing is a dynamic indentation where combining multi-directional stress distribution in sandwich panels is not an easy task for description. The main aim of this work is to compare sandwich panels with two different types of core (3D inverted honeycomb and conventional honeycomb structures with similar specific densities). Based material of the aforementioned cores is photopolymer resin which allows the manufacturing of complex shapes of cores by stereolithography technology. All specimens, equipped with a spreading thin layer of polyethylene shell, are subjected to dynamic penetration to evaluate the mechanical behavior, penetration resistance, and energy-absorbing capability at different impact velocities. An in-house developed direct impact Hopkinson bar is used for dynamic indentation experiments. The loading apparatus is equipped with strain gauges and the measured signals are used for the calculation of an applied force and impact velocity. A pair of highspeed cameras are used for optical inspection of the experiments. A targeted camera is used for evaluating the velocity of the projectile using the digital image correlation method (DIC) for comparison with strain-gauge measurement, and an overview camera is used for capturing the surroundings of the impact plane.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Josef Svoboda; Ing. Přemysl Toman; Zeman, J.; Abraham, D.; Heřmanová, J.; doc. Ing. Petr Bouchner, Ph.D.; Ing. Josef Mík, Ph.D.; Ing. Jan Vyčichl, Ph.D.; Skarolek, P.

Publikováno:

2022

Anotace:

Technical report describing tech details of the motorcycle EVO 2.0 Electric for the competition Moto Engineering Italy in 2022 according to the regulations of Motorsport Engineering Society.

Typ:

Technická zpráva cizojazyčně

Autoři:

Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 285-288), ISBN 978-80-86246-51-2, ISSN 1805-8256

Anotace:

Research into the mechanical behaviour of lattice structures and metal foams at high strain rates using experiments based on a direct impact Hopkinson bar (DIHB) method has been recently proposed to overcome several limitations of the conventional split Hopkinson pressure bar (SHPB). Especially, the socalled open Hopkinson pressure bar (OHPB), a modification of DIHB with strain measurement points on both bars, has been proved to be a suitable experimental technique for testing of materials with low mechanical impedance. However, experimental testing is usually limited in terms of resources and, hence, it is convenient to employ numerical methods to predict the results of experiments and, if necessary, adjust the parameters of the experimental procedure based on the preceding numerical analysis of the problem. Developing a numerical model of the whole experimental set-up is, thus, a key method to achieve a reliable analysis. In this paper, we present a numerical model of an OHPB apparatus and demonstrate its suitability for inverse numerical simulations of the closed-cell aluminium foam.

DOI:

10.21495/51-2-285

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. et Ing. Radim Dvořák; Ing. Michaela Jurko; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2022, Dynamic Behaviour of Additively Manufactured Structures & Materials, Freiburg im Breisgau, Albert-Ludwigs-Universität Freiburg), p. 187-192)

Anotace:

We demonstrate numerical modelling of the mechanical response of auxetic structures sub- jected to dynamic uniaxial compressive load- ing in split Hopkinson pressure bar (SHPB) at the strain rates of 1500 s−1 and 3000 s−1. The stress-strain characteristics as well as com- pressive strain dependent Poisson’s ratio of re-entrant honeycomb and missing-rib aux- etic lattices are assessed in LS-DYNA simula- tions with explicit time integration. Numer- ical results are supported by SHPB experi- ments utilized for both calibration of finite el- ement modeling and verification of the sim- ulations. The studied lattices were additively manufactured by laser powder bed fusion from 316L stainless steel. The numerical aspects of the simulations together with the influence of the 3D printing quality on the reliability of the results are discussed.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Michaela Jurko; Ing. Václav Rada; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2022, Dynamic Behaviour of Additively Manufactured Structures & Materials, Freiburg im Breisgau, Albert-Ludwigs-Universität Freiburg), p. 103-110)

Anotace:

Open Hopkinson Pressure Bar (OHPB) appa- ratus is used, together with conventional split Hopkinson pressure bar (SHPB), for dynamic testing of additively manufactured cellular me- tamaterials at intermediate and high strain rates. Benefits of the OHPB testing method over standard established methods are dis- cussed. The investigated metamaterials in- clude various types of auxetic lattices manu- factured from powdered austenitic steel by powder bed fusion technology. It is found out that the investigated type of metamate- rials exhibits significant strain rate sensitivity of the stress-strain curves as well as of the apparent auxeticity. Moreover, its deforma- tion mechanism changes with the increasing impact velocity as the buckling of the individ- ual struts is reduced by the inertia effects.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Václav Rada; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Mauko, A.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2022, Materials, 15 (3), ISSN 1996-1944

Anotace:

The main aim of the study was to analyse the strain rate sensitivity of the compressive deformation response in bulk 3D-printed samples from 316L stainless steel according to the printing orientation. The laser powder bed fusion (LPBF) method of metal additive manufacturing was utilised for the production of the samples with three different printing orientations: 0◦, 45◦, and 90◦. The specimens were experimentally investigated during uni-axial quasi-static and dynamic loading. A split Hopkinson pressure bar (SHPB) apparatus was used for the dynamic experiments. The experiments were observed using a high-resolution (quasi-static loading) or a high-speed visible-light camera and a high-speed thermographic camera (dynamic loading) to allow for the quantitative and qualitative analysis of the deformation processes. Digital image correlation (DIC) software was used for the evaluation of displacement fields. To assess the deformation behaviour of the 3D-printed bulk samples and strain rate related properties, an analysis of the true stress–true strain diagrams from quasi-static and dynamic experiments as well as the thermograms captured during the dynamic loading was performed. The results revealed a strong strain rate effect on the mechanical response of the investigated material. Furthermore, a dependency of the strain-rate sensitivity on the printing orientation was identified.

DOI:

10.3390/ma15030941

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Jan Falta; Yunus Yilmaz, E.

Publikováno:

2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 1-416), ISBN 978-80-86246-51-2, ISSN 1805-8256

Anotace:

Masked Stereolithography (MSLA) is an additive manufacturing process based on the photocuring of an entire printed layer of resin at once with the use of a UV light source, in this case a monochrome LCD display. The prints can be used not only for visualization of structures and parts, but also for development of elements of real constructions. The main objective of the study is to describe the mechanical properties under different types of loading, in particular to analyze the strain-rate sensitivity of compression response in bulk and inverted honeycomb lattice samples with three different strut widths. The specimens were experimentally investigated under quasi-static and high strain rate loading. Split Hopkinson Pressure Bar (SHPB) apparatus was used for the high strain rate experiments. The experiments were observed with a high-speed camera to allow analysis of the deformation processes. Digital Image Correlation (DIC) software was used to evaluate the displacement and stress fields. The results revealed a strong effect of strain rate, especially between quasistatic and high strain rate loads. An auxetic behavior was observed for the inverted honeycomb structure, which depends on the thickness of the struts.

DOI:

10.21495/51-2-93

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Vít Malinovský, Ph.D.

Publikováno:

2021, Neural Network World, 31 (4), p. 239-259), ISSN 1210-0552

Anotace:

Abstract: This paper deals with problems of processing freight statistic data into the form of time series and analysing consequent results by means of two completely different methods. The first method for calculating chosen transport trends uses the transport model Trans-Tools based on conventional mathematical and statistical functions while the second one uses the Scikit Learn software providing users with development environment including algorithms of neural networks. The obtained results are similar to a certain extent which shows new possibilities of progressive use of neural networks in future and enables modern approach to analysing time series not only in transportation sector. Comparative analysis of results obtained from the same transport data processed by standard mathematical (Trans-Tool) method and neuron-network (Scikit Learn) method as well as a research focused on some trends development within the scope of freight transport in EU represent goals of this work.

DOI:

10.14311/NNW.2021.31.013

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Ing. Václav Rada; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2021, Metals — Open Access Metallurgy Journal, 11 (8), ISSN 2075-4701

Anotace:

Compressive deformation behaviour of additively manufactured lattice structures based on re-entrant tetrakaidecahedral unit-cell geometry were experimentally investigated under quasi-static and dynamic loading conditions. Specimens of four different structures formed by three-dimensional periodical assembly of selected unit-cells were produced by a laser powder bed fusion technique from a powdered austenitic stainless steel SS316L. Quasi-static compression as well as dynamic tests using split Hopkinson pressure bar (SHPB) apparatus at two strain-rates were conducted to evaluate the expected strain-rate sensitivity of the fundamental mechanical response of the structures. To evaluate the experiments, particularly the displacement fields of the deforming lattices, optical observation of the specimens using a high-resolution camera (quasi-static loading) and two synchronised high-speed cameras (SHPB experiments) was employed. An in-house digital image correlation algorithm was used in order to evaluate the anticipated auxetic nature of the investigated lattices. It was found that neither of the investigated structures exhibited auxetic behaviour although strain-rate sensitivity of the stress–strain characteristics was clearly identified for the majority of structures.

DOI:

10.3390/met11081196

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Mauko, A.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; Ing. Václav Rada; Ing. Michaela Jurko; doc. Ing. Petr Zlámal, Ph.D.; Vesenjak, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ren, Z.

Publikováno:

2021, Metals — Open Access Metallurgy Journal, 11 (1), ISSN 2075-4701

Anotace:

The mechanical behaviour of three different auxetic cellular structures, hexa-chiral 2D, tetra-chiral 2D and tetra-chiral 3D, was experimentally investigated in this study. The structures were produced with the powder bed fusion method (PBF) from an austenitic stainless steel alloy. The fundamental material mechanical properties of the sample structures were determined with classic quasi-static compressive tests, where the deformation process was captured by a high-resolution digital camera. The Split Hopkinson Pressure Bar (SHPB) apparatus was used for dynamic impact testing at two impact velocities to study the strain-rate dependency of the structures. Two synchronised high-speed cameras were used to observe the impact tests. The captured images from both quasi-static and dynamic experiments were processed using a custom digital image correlation (DIC) algorithm to evaluate the displacement/strain fields and the Poisson’s ratio. Predominant auxetic behaviour was observed in all three structures throughout most of the deformation process both under quasi-static and impact loading regimes. The tetra-chiral 2D structure showed the most significant auxetic behaviour. Significant stress enhancement in all tested structures was observed in dynamic testing. The Poisson’s ratio strain-rate dependency was confirmed for all three auxetic structures.

DOI:

10.3390/met11010052

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Václav Rada; Adorna, M.; Bronder, S.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2021, International Journal of Impact Engineering, 148, ISSN 0734-743X

Anotace:

Direct impact testing with a Hopkinson bar is, nowadays, a very popular experimental technique for investigating the behavior of cellular materials, e.g., lattice metamaterials, at high strain-rates as it overcomes several limitations of the conventional Split Hopkinson Pressure Bar (SHPB). However, standard direct impact Hopkinson bars (DIHB) have only single-sided instrumentation complicating the analysis. In this paper, a DIHB apparatus instrumented with conventional strain-gauges on both bars (a so called Open Hopkinson Pressure Bar - OHPB) is used for dynamic impact experiments of cellular materials. Digital image correlation (DIC) is used as a tool for investigating the displacements and velocities at the faces of the bars. A straight-forward wave separation technique combining the data from the strain-gauges with the DIC is adopted to increase the experiment time window multiple times. The experimental method is successfully tested at impact velocities in a range of 5-30 m/s with both linear elastic and visco-elastic bars of a medium diameter. It is shown that, under certain circumstances, a simple linear elastic model is sufficient for the evaluation of the measurements with the visco-elastic bars, while no additional attenuation and phase-shift corrections are necessary. The applicability of the experimental method is demonstrated on various experiments with conventional metal foams, hybrid foams, and additively manufactured auxetic lattices subjected to dynamic compression.

DOI:

10.1016/j.ijimpeng.2020.103767

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Adorna, M.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Glinz, J.; Ing. Michaela Jurko; Ing. Tomáš Doktor, Ph.D.; Mauko, A.; doc. Ing. Daniel Kytýř, Ph.D.; Vesenjak, M.; Duarte, I.; Ren, Z.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2021, Materials Science and Engineering A - Structural Materials: Properties, Microstructure and Processing, 800, ISSN 0921-5093

Anotace:

Light-weight cellular solids, such as aluminium foams, are promising materials for use in ballistic impact mitigation applications for their high specific deformation energy absorption capabilities. In this study, three different types of aluminium alloy based in-house fabricated cellular materials were subjected to dynamic penetration using the in-house experimental setup to evaluate their deformation and microstructural response. Two-sided direct impact Hopkinson bar apparatus instrumented with two high-speed cameras observing the impact area and the penetrated surface of the specimens was used. Advanced wave separation technique was employed to process strain-gauge signals recorded during penetration. Images captured by one of the cameras were processed using an in-house Digital Image Correlation method with sub-pixel precision, that enabled validation of the wave separation results of the strain-gauge signals. The second camera was used to observe the penetration into the tested specimens for correct interpretation of the measured signals with respect to derived mechanical and microstructural properties at different impact velocities. Differential X-ray computed tomography of selected specimens was performed, which allowed for an advanced pre- and post-impact volumetric analysis. Results of performed experiments and elaborate analysis of the measured experimental data are shown in this study.

DOI:

10.1016/j.msea.2020.140096

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Bronder, S.; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.

Publikováno:

2021, Advanced Engineering Materials, 23 (5), p. 1-15), ISSN 1438-1656

Anotace:

With their increased energy absorption capacity, auxetic materials are perfectly fit to develop new, enhanced lightweight crash absorbers for cars. Herein, the mass distribution along the struts is optimized via finite element analysis with a parameterized optimization. Four different auxetic unit cells are taken from the literature and their struts parameterize, the models simulate, and the mass specific energy absorption capacity optimizes. The two models with the highest energy absorption capacity are then selected for experimental investigation and produced by additive manufacturing from a polymer. To further enhance the mechanical properties, the specimens are electrochemically coated with nickel and the polymer molten out by pyrolysis. Those Ni/polymer hybrids are subjected to quasistatic and dynamic impact experiments. Only a small strain rate sensitivity can be detected under dynamic loading, namely, a higher plastic collapse and higher plateau stress. The hollow struts are folding instead of bending, which render them much weaker than predicted by the simulation. In conclusion, it is possible to improve existing crash absorber elements with tailored auxetic hybrid structures. They absorb higher amounts of energy without changing their stiffness under dynamic loading while saving mass and cost.

DOI:

10.1002/adem.202001393

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Michaela Jurko; Mauko, A.; Valach, J.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2021, Advanced Engineering Materials, 23 (1), ISSN 1438-1656

Anotace:

Metamaterials produced using additive manufacturing represent advanced structures with tunable properties and deformation characteristics. However, the manufacturing process, imperfections in geometry, properties of the base material as well as the ambient and operating conditions often result in complex multiparametric dependence of the mechanical response. As the lattice structures are metamaterials that can be tailored for energy absorption applications and impact protection, the investigation of the coupled thermomechanical response and ambient temperature‐dependent properties is particularly important. Herein, the 2D re‐entrant honeycomb auxetic lattice structures additively manufactured from powdered stainless steel are subjected to high strain rate uniaxial compression using split Hopkinson pressure bar (SHPB) at two different strain rates and three different temperatures. An in‐house developed cooling and heating stages are used to control the temperature of the specimen subjected to high strain rate impact loading. Thermal imaging and high‐speed cameras are used to inspect the specimens during the impact. It is shown that the stress–strain response as well as the crushing behavior of the investigated lattice structures are strongly dependent on both initial temperature and strain rate.

DOI:

10.1002/adem.202000669

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ozcan, Y.; Tunc, L.T.; Ing. Ján Kopačka, Ph.D.; Cetin, B.; Sulitka, M.

Publikováno:

2021, The International Journal of Advanced Manufacturing Technology, 114 (11-12), p. 3581-3596), ISSN 0268-3768

Anotace:

Controlled depth abrasive waterjet machining (AWJM) is an unconventional and promising process for materials introducing challenges in conventional machining for high value manufacturing (HVM) industries such as aerospace and automotive. In such applications, waterjet acts as a flexible cutting tool compared to conventional milling. The kerf profile, i.e. the removed material volume, nonlinearly depends on the process parameters such as water pressure, jet traverse speed, abrasive rate, and stand-off-distance unlike the deterministic case in mechanical milling. Thus, prediction of kerf profile, i.e. width, depth, and shape, is of great importance for accurate and efficient process development and tool path generation in AWJM. In this paper, a novel analytical model is proposed for prediction of kerf profile, relying on conservation of energy and momentum, where the material removal is related to the machinability number of the workpiece material, so that the requirement of calibration tests is eliminated. Then, the proposed AWJM process model is used in a framework to predict 3D in-process workpiece (IPW) geometry, which is represented using signed distance field (SDF) approach. The process model is verified by experimental results with an average error of 15%, where the machine profiles are measured by confocal optical microscopy. The IPW simulation model is verified by variable jet traverse speed AWJM experiments, considering the significant effect of jet traverse speed on the kerf depth. The machined specimens are sectioned along the jet traverse direction and the cross section of the test pieces is visually compared with the simulations. The machined profiles introduced some amount of undulated profile, which may be attributed to the non-consistent abrasive supply in the system. It is shown that the proposed IPW simulation approach demonstrates a reasonable accuracy to plan controlled depth AWJM processes.

DOI:

10.1007/s00170-021-07131-1

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Glinz, J.; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ayalur-Karunakaran, S.; Zabler, S.; Kastner, J.; Senck, S.

Publikováno:

2021, Journal of Materials Science, 56 (16), p. 9712-9727), ISSN 0022-2461

Anotace:

In this work, we present a multimodal approach to three-dimensionally quantify and visualize fiber orientation and resin-rich areas in carbon-fiber-reinforced polymers manufactured by vacuum infusion. Three complementary image modalities were acquired by Talbot–Lau grating interferometer (TLGI) X-ray microcomputed tomography (XCT). Compared to absorption contrast (AC), TLGI-XCT provides enhanced contrast between polymer matrix and carbon fibers at lower spatial resolutions in the form of differential phase contrast (DPC) and dark-field contrast (DFC). Consequently, relatively thin layers of resin, effectively indiscernible from image noise in AC data, are distinguishable. In addition to the assessment of fiber orientation, the combination of DPC and DFC facilitates the quantification of resin-rich areas, e.g., in gaps between fiber layers or at binder yarn collimation sites. We found that resin-rich areas between fiber layers are predominantly developed in regions characterized by a pronounced curvature. In contrast, in-layer resin-rich areas are mainly caused by the collimation of fibers by binder yarn. Furthermore, void volume around two adjacent 90°-oriented fiber layers is increased by roughly 20% compared to a random distribution over the whole specimen.

DOI:

10.1007/s10853-021-05907-0

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Kolman, R.; Ren, Z.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2020

Anotace:

This doctoral thesis is focused on the experimental analysis of cellular meta-materials subjected to a dynamic impact with a high strain-rate. In particular, additively manufactured auxetic lattices (structures with a negative Poisson’s ratio) are investigated. Two in-house Hopkinson bar experimental setups are developed for the testing of the structures: i) a conventional Split Hopkinson Pressure Bar (SHPB, Kolsky bar), and ii) a novel direct impact Open Hopkinson Pressure Bar (OHPB). Both setups are tailored for the application on the low impedance materials and are used for the experiments subjecting the cellular meta-materials to a high strain-rate uni-axial compression. In the thesis, the developed apparatuses, the instrumentation, evaluation methods and the experimental program are described in detail. The experiments are optically inspected using several high-speed cameras and a digital image correlation technique is employed for the advanced analysis of the deformation behavior of the meta-materials. Using the data from several experimental campaigns, the strain-rate sensitivity of the selected auxetic lattices and their Poisson’s ratio is investigated in detail. It is found out that the auxetic structures are, in general, strain-rate sensitive and their Poisson’s ratio is both strain-rate and strain dependent. Other representative results exploiting the deformation behavior of cellular materials, e.g., hybrid open-cell foams and hybrid hollow strut auxetic lattices are also presented in the study.

Typ:

Disertační práce (PhD)

Autoři:

Ing. Josef Svoboda; Ing. Přemysl Toman; Zeman, J.; Abraham, D.; Ing. Jan Vyčichl, Ph.D.; Heřmanová, J.; Orlický, A.; Malínský, V.; Dáňa, R.; Jan Válek, DiS.; doc. Ing. Petr Bouchner, Ph.D.; Ing. Josef Mík, Ph.D.; doc. Ing. Stanislav Novotný, Ph.D.

Publikováno:

2020

Anotace:

In the scope of the Motostudent competition there was created complex project of the whole motorcycle in the category of Electro bikes. Report contains conceptual design, detailed design, prototyping and development.

Typ:

Technická zpráva cizojazyčně

Autoři:

Ing. Přemysl Toman; Ing. Josef Svoboda; Ing. Jan Vyčichl, Ph.D.; Malínský, V.; Abraham, D.; Zeman, J.; Dáňa, R.; doc. Ing. Petr Bouchner, Ph.D.; Ing. Josef Mík, Ph.D.; Ing. Jiří First

Publikováno:

2020

Anotace:

In the research report we focus on the state of the art of the propossed innovation, moreover there is declared the research process, proof of concept, market viability and discussion of the proposed innovation of variable geometry of the racing motorcycle. In the repoert there are as well mentioned results of the topological and structural optimizations of the whole assembly as well as mannufacturing drawings.

Typ:

Výzkumná zpráva cizojazyčně

Autoři:

Ing. Petr Koudelka, Ph.D.; Keršner, Z.; Vesenjak, M.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2020

Anotace:

The dissertation thesis is focused on the numerical modelling of the mechanical response of auxetic structures to uniaxial compressive loading. According to the primary application of auxetics in terms of deformation energy mitigation, where their unique characteristics arising from the negative Poisson’s ratio of the structure, high strain rate response is emphasised. Additionally, quasi-static characteristics are assessed to obtain reference data for the evaluation of the strain-rate dependency induced particularly by micro-inertia effects. Mechanical properties are studied using stress-strain characteristics, whereas the microstructural response is evaluated based on the function of Poisson’s ratio. In the thesis, three auxetic unit-cells having uni- or bi-axial auxetic characteristics are considered. The structures are developed by a periodic assembly of unit-cells in the respective spatial directions. Due to the complex deformation response of the auxetic structures, the reference data for the development of numerical simulations are obtained from the experiments with the samples of structures manufactured using 3D printing. Dynamic loading is performed using a Split Hopkinson Pressure Bar (SHPB) apparatus, while an approach to the numerical simulations consisting of the development of a full-scale virtual SHPB for an explicit time integration scheme in LS-DYNA was selected. In the dynamic simulations, geometrical models of the lattices precisely corresponding to the geometry of the structures for the 3D printing are used. The numerical aspects of the simulations together with the influence of the 3D printing quality on the reliability of the results are discussed. The ability of the numerical simulations to describe the deformation response of the investigated auxetic lattices is assessed based on the numerical stress-strain curves and the graphs of the strain-dependent Poisson’s ratio.

Typ:

Disertační práce (PhD)

Autoři:

Ing. Tomáš Doktor, Ph.D.; Gutermann, M.; Rusnáková, S.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2020

Anotace:

The thesis deals with the investigation of the mechanical behaviour of cellular materials at higher strain-rates and enhancement of their energy absorption capabilities. Three types of cellular solids were tested: closed- and open-cell aluminium foam and SLS printed auxetic lattices. To induce a strain-rate sensitive response in open-cell structures, different types of polymeric fillers were tested (polyurethane putty, polyurethane foam and ordnance gelatin) to form Interpenetrating- phase composites (IPCs). At the micro level, the tests were performed using an in-house apparatus in conjunction with the optical strain measurement using Digital Image Correlation (DIC). At the macro-level, for the investigation of the cellular structure a time-lapse X-ray tomography of the compression test was performed. Two types of impact tests were used to cover a broader range of the strain-rates, drop tower and Hopkinson bar (SHPB). A strain-rate sensitive response was observed at moderate strain-rates in the ordnance gelatin and IPC, while the response of unfilled aluminium foam remained unchanged. The SHPB tests showed a strain-rate sensitivity in the energy absorption for all the tested materials. The DIC strain measurement of the SHPB impact tests of the polymer-filled auxetics showed a reduction in the auxetic nature with the filling.

Typ:

Disertační práce (PhD)

Autoři:

Ing. Luboš Nouzovský, Ph.D.; Ing. Martin Jacura, Ph.D.; Ing. Ondřej Doležal; Ing. Michal Drábek, Ph.D.; Ing. Patrik Horažďovský, Ph.D.; Ing. Josef Mík, Ph.D.; Ing. Jiří Růžička, Ph.D.; Ing. Michaela Kalivodová; Ing. Petr Richter, Ph.D.; Ing. Michaela Jurko; doc. Ing. Michal Matowicki, Ph.D.

Publikováno:

2020, ISBN 978-80-01-06793-2

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2019, ISBN 978-80-86246-45-1

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 17-20), ISBN 978-80-01-06670-6, ISSN 2336-5382

Anotace:

Presented paper deals with experimental study on compressive properties of auxetics with controlled stiffness of strut joints. The variable strut joints properties were simulated by adding extra amount of material in the struts’ intersection regions. Four groups of inverted honeycomb structures were prepared by multi-jet 3D printing and tested in quasi-static compression. The structure collapsed gradually, however after the first collapse, failure in entire cross-section occurred due to the brittle nature of the base material. The behavior up to the first collapse was consistent among the specimens within each group, while differed slightly subsequently. With higher reinforcement in the joints, results showed increasing stress at the first collapse (ultimate compressive stress) while the strain at the first collapse remained unchanged. The auxetic behaviour became less significant with increasing joints’ reinforcement.

DOI:

10.14311/APP.2019.25.0017

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Luksch, J.; Felten, M.; Fries, M.; Jung, A.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, International Conference on Nonlinear Solid Mechanics - ICoNSoM2019, Palazzo Argiletum, Roma, Italy), p. 131-131)

Anotace:

Cellular solids, such as metal foams, hybrid foams, 3D printed lattices or additively manufactured auxetic structures are complex lightweight cellular materials with high energy absorption capabilities and possible functionally graded material properties. Engineering applications of such materials require optimization of their design, and thus their mechanical behavior under the representative loading conditions (i. e., dynamic impact, blast). The design and optimization procedures require a relevant material model based on the experimental investigation of the constructs. In this study, the application of the Digital Image Correlation (DIC) technique on the cellular solids in quasi-static and dynamic compression is discussed and the representative results of the method in this application are presented. Here, digital image correlation is used as an advanced method for the complex experimental analysis of the displacement and strain fields of several cellular solids under quasi-static compression and high strain-rate loading using the Split Hopkinson Pressure Bar (SHPB) apparatus. The data from the experiments with the specimens of the selective laser sintered auxetic lattices, made of powdered austenitic steel, and with hybrid nickel-polyurethane aluminum foam were processed using a custom digital image correlation tool. Results covering the evaluation of the displacement and strain fields, different methods for evaluation of Poisson’s ratio, and the analysis of the digital image correlation reliability are presented in the study. The study is focused particularly on the application of the digital image correlation on the data captured by a high-speed camera during high strain-rate experiments and the analysis of the cellular solids during dynamic impact. Comparison of the digital image correlation results with the other methods, its limitations and the actual challenges in this field are also discussed in the study.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Jan Falta; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 32-35), ISBN 978-80-01-06670-6, ISSN 2336-5382

Anotace:

The presented paper is focused on embedding of the serially manufactured piezo-electric impact load-cell into Split Hopkinson Pressure Bar (SHPB) for a direct force measurement during dynamic loading. Conventionally, during the SHPB test dynamic force equilibrium is investigated by a comparison of the transmitted signal wave and the difference between the incident and reflected signals waves to the incident bar, measured by strain gauges \cite{bib1}. However, in the experiments with specimens with low \linebreak mechanical impedance, a major portion of the incident wave is reflected back on the boundary between the bar and the specimen. Comparison between two-large amplitude incident and reflected pulse and \linebreak a small-amplitude transmitted pulse can be influenced by large error and resulting force equilibrium can be inaccurate. Therefore, a piezo-electric quartz impact force transducer was used to directly measure the axial forces in the vicinity of the specimen end surfaces, allowing to analyze the force equilibrium which is an essential characteristic for reliable measurement. Measured values from strain gauges were compared with values obtained from force transducer, to verify the validity of the acquired signals which will increase the reliability of the measured data. The presented solution will help to determine the mechanical properties of advanced materials which is necessary for investigation of complex modern material structures behaviour.

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Adorna, M.; Bronder, S.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 1-5), ISBN 978-80-01-06670-6, ISSN 2336-5382

Anotace:

Three different tools for Digital Image Correlation (DIC) were used for evaluation of dynamic experiments performed using custom Open Hopkinson Pressure Bar (OHPB) apparatus. High strain-rate measurements were performed on specimens of advanced cellular materials with predefined structure and negative Poisson's ratio. Low impedance polymethyl methacrylate (PMMA) bars instrumented with foil strain-gauges were used for dynamic loading of the specimens. Experiments were observed using a pair of high-speed cameras for imaging of loading process in sufficient quality. Custom developed evaluation DIC tool implemented in Matlab, open-source Matlab tool (NCorr) and commercial DIC software (ISTRA 4D) were all used for evaluation of image sequences recorded by high-speed cameras. Comparison of results obtained using all three different DIC tools and results of complementary strain-gauge measurement are shown in this paper. Verification of reliability of custom made DIC software tool is presented.

DOI:

10.14311/APP.2019.25.0001

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Adorna, M.; Reis, M.; Jung, A.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, International Conference on Nonlinear Solid Mechanics - ICoNSoM2019, Palazzo Argiletum, Roma, Italy), p. 128-128)

Anotace:

In this study, two different tools for Digital Image Correlation (DIC) were used for evaluation of three-point bending tests performed using an in-house bending device. Isolated struts of an open cell aluminium foam were investigated in this study. An in-house multifunctional loading device equipped with a precise load cell with a force sensor was used to perform the bending. Experiments were observed using a pair of CCD cameras with a telecentric lense for imaging of the loading process in a sufficient quality. That enabled to perform 3D DIC evaluation using both commercial and open-source DIC software tools. Synchronisation of the cameras, the records and the stroke of the bending device was achieved using a custom Labview control software tool. Calibration of the camera pair, which was necessary for the 3D DIC evaluation, was carried out using Direct Linear Transformation (DLT). To further investigate the behaviour of the isolated struts of the aluminium foam, a photogrammetric method was used to obtain 3D models of every strut. The models allowed for a precise measurement of the struts dimensions necessary for material characteristics determination. A modified open-source Matlab tool [1] and a commercial DIC software (ISTRA 4D) were used for evaluation of the image sequences recorded by the CCD cameras. Coparison of the results obtained using both different 3D DIC tools and the results derived directly from the stroke of the measuring device are presented in this study.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Vít Malinovský, Ph.D.; Meyer-Rühle, O.; Kyster-Hansen, H.; Böhmann, A.; Heinrich, Ch.; Leonhardt, S.; Zuiver, H.

Publikováno:

2019, 2019 Konference - 25 let Fakulty dopravní, Praha, České vysoké učení technické v Praze), ISBN 978-80-01-06545-7

Anotace:

The paper deals with problems of determination and assessment of external factors (dependency on fossil fuels, GFG production, congestions, and road fatalities) for processing by a transport model by means of common mathematical and econometical methods (Trans-Tools model). Results are used as grounds for forecasting freight transport trends in time horizons 2035 and 2050.

Typ:

Stať ve sborníku z fakultní konference cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 21-24), ISBN 978-80-01-06670-6, ISSN 2336-5382

Anotace:

In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the filling material were tested, (i) ordnance gelatin, (ii) low expansion polyurethane foam, and (iii) polyurethane putty. To evaluate their impact energy absorption bulk samples of the selected materials were tested in compression loading mode at strain-rates 1000 s−1 to 4000 s−1 . The high strain-rate compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was equipped with PMMA bars to enable testing of cellular materials with low mechanical impedance. Based on the comparative measurement response to compression at both low and high strain-rates was analysed. The results show a significant strain-rate sensitivity of the ordnance gelatin and of the polyurethane putty, while strain-rate effect in the polyurethane foam was not observed.

DOI:

10.14311/APP.2019.25.0021

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Bronder, S.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Adorna, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.

Publikováno:

2019, Temperature dependence of material behaviour at high strain-rate, Politecnico di Torino), ISBN 978-88-85745-27-8

Anotace:

Two types of the hybrid polymer-nickel auxetic specimens were subjected to the quasi-static compression and compressive impact loading using Open Hopkinson Pressure Bar. Two variants of the 3D re-entrant auxetic lattice were used: i) structures with rectangular struts and ii) structure with rounded struts. The specimens were numerically optimized, prepared using computer aided design, and the base constructs were 3D printed from VisiJet EX200 polymer. The constructs were then coated using the electrodeposition of the nanocrystalline nickel in two nominal thicknesses of the coating (60 μm and 120 μm). After the coating process, the core part of the constructs was removed by the burning-out of the polymer at elevated temperature. The structures were subjected to the quasi-static compression and simultaneously inspected using an CCD camera, while Hopkinson bar was used for the impact loading of the specimens at two different impact velocities (ca. 5 m/s and 26 m/s). Dynamic experiments were observed with a pair of high-speed cameras and an infrared camera. The high-speed camera images were processed using a custom digital image correlation algorithm. Mechanical as well as thermal behavior of the hybrid auxetic structures subjected to the different loading conditions was analyzed and summarized in this paper.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Reis, M.; Adorna, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.

Publikováno:

2019, Advanced Engineering Materials, 21 (7), ISSN 1438-1656

Anotace:

Digital image correlation (DIC) is a common software tool to measure displacement and strain fields on the surface of a specimen during mechanical testing. Due to its low requirements on the experimental setup and the simple usability it is widely spread in the community of applied mechanics. Nevertheless, the real noise of the method often stays uninvestigated. Therefore, this work shows different approaches to measure errors in DIC. The present contribution proves lighting as the main error source and it shows that a series of static images allows to estimate the error level of the DIC before performing the experiment. To give a proof of concept of the improved DIC setup, three-point bending tests on single struts of aluminum foam are performed and evaluated.

DOI:

10.1002/adem.201900092

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. et Ing. Radim Dvořák; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, 10th International Conference Auxetics and other materials and models with ”negative” characteristics - abstract book, Poznań, Institute of Molecular Physics), ISBN 978-83-933663-8-5

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. et Ing. Radim Dvořák; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 25-31), ISBN 978-80-01-06670-6, ISSN 2336-5382

Anotace:

The paper aims at the numerical simulation of the wave propagation in compressive Split Hopkinson Pressure Bar (SHPB) experiment. The paper deals with principles of SHPB measurement, optimisation of a numerical model and techniques of pulse shaping. The parametric model of the typical SHPB configuration developed for LS-DYNA environment is introduced and optimised (in terms of element size and distribution) using the sensitivity study. Then, a parametric analysis of a geometric properties of the pulse shaper is carried out to reveal their influence on a shape of the incident pulse. The analysis is algorithmized including the pre- and post-processing routines to enable automated processing of numerical results and comparison with the experimental data. Results of the parametric analysis and the influence of geometric properties of the pulse shaper (diameter, length) on the incident wave are demonstrated.

DOI:

10.14311/APP.2019.25.0025

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2019, Engineering Mechanics 2019: Book of full texts, Prague, Institute of Thermomechanics, AS CR, v.v.i.), p. 97-101), ISBN 978-80-87012-71-0, ISSN 1805-8248

Anotace:

In this paper, an implementation of Split Hopkinson Pressure Bar (SHPB) and its modification Open Hopkinson Pressure Bar (OHPB) for testing of cellular structures is presented. Dynamic testing of materials with low mechanical impedance is very demanding in terms of achieving the requested experimental device performance. Key elements of the Hopkinson bar instrumentation that were successfully employed in dynamic testing of cellular materials are presented in this paper. Detailed overview of the strain-gauges instrumentation including our best practices for installation and noise reduction is provided. Information about the instrumentation of Hopkinson bar with high-speed cameras are also given. To demonstrate the performance of the proposed instrumentation some examples of a typical results are summarized in the text.

DOI:

10.21495/71-0-97

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Adorna, M.; Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2019, Engineering Mechanics 2019: Book of full texts, Prague, Institute of Thermomechanics, AS CR, v.v.i.), p. 29-33), ISBN 978-80-87012-71-0, ISSN 1805-8248

Anotace:

In this paper, digital image correlation method (DIC) is introduced as a tool for evaluation of high strain-rate experiments perfomed using Hopkinson Bar apparatus. Samples of advanced cellular materials with predefined periodic structure and negative Poisson’s ratio (auxetic structures) were investigated in this study. In-house Hopkinson Pressure Bar apparatus was used to perform the impact experiments and the experimental setup was observed using a pair of high-speed cameras. Custom DIC software tool was used to evaluate highspeed cameras records. Selected representative results of DIC applications on Hopkinson Bar experiments are provided in this paper.

DOI:

10.21495/71-0-29

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.; Luksch, J.; Ing. Michaela Jurko; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, Advanced Engineering Materials, 21 (8), ISSN 1438-1656

Anotace:

This paper deals with experimental investigation into a strain‐rate dependent function of Poisson's ratio of three auxetic structures subjected to compressive loading. The missing rib, the 2D re‐entrant honeycomb, and the 3D re‐entrant honeycomb lattices printed using selective laser sintering from powdered SS316L austenitic steel are investigated. The samples are subjected to uni‐axial compression under quasi‐static conditions and dynamic conditions using the Split Hopkinson Pressure Bar (SHPB). The deforming specimens are optically observed in order to apply a digital image correlation for evaluation of the in‐plane displacement and strain fields. From the calculated strain fields, the function of Poisson's ratio is calculated for each experiment using different methods taking specific regions of interest of the specimen microstructures into account. The obtained functions of Poisson's ratio are plotted for each microstructure and strain‐rate. The analysis of the results shows that the strain‐rate has a significant influence on the deformation characteristics of all the investigated microstructures yielding differences in the magnitude of the minima of Poisson's ratio and the differences in the maximum overall compressive strain, where the lattices are still auxetic.

DOI:

10.1002/adem.201900204

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 68-72), ISBN 978-80-01-06670-6, ISSN 2336-5382

Anotace:

The paper is focused on evaluation of the relation between mechanical properties of 3D printed stainless steel 316L-0407 and printing direction (i.e. the orientation of the part which is being printed in the manufacturing device) subjected to compressive loading at different strain-rates. In order to evaluate the strain rate dependency of the 3D printed material’s compressive characteristics, dynamic and quasi-static experiments were performed. Three sets of bulk specimens were produced, each having a different printing orientation with respect to the powder bed plane (vertical, horizontal and tilted). To assess the deformation behaviour of the 3D printed material, compressive stress-strain diagrams and compressive yield strength and tangent modulus were evaluated.

DOI:

10.14311/APP.2019.25.0068

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Petr Koudelka, Ph.D.; Ing. Michaela Jurko; Luksch, J.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, 10th International Conference Auxetics and other materials and models with ”negative” characteristics - abstract book, Poznań, Institute of Molecular Physics), p. 37-39), ISBN 978-83-933663-8-5

Anotace:

n this work, selective laser sintered (SLS) auxetic lattices printed from the powdered 316L–0407 austenitic steel were subjected to compressive loading at several strain-rates. Three types of the auxetic lattices were tested: i) 2D re-entrant honeycomb, ii) 2D missing rib, and iii) 3D re-entrant honeycomb. The structures were subjected to the quasi-static uni-axial compression using a standard electromechanical loading device. The experiments were observed using a CCD camera. In dynamic experiments, the specimens were compressed at four different strain-rates using two Hopkinson bar techniques. Data recorded by the strain-gauges mounted on the measurement bars were used for evaluation of the mechanical behavior of the specimen (e. g., stress-strain and strain-rate-strain diagrams). A custom digital image correlation (DIC) tool based on Lucas-Kanade tracking algorithm was used for the advanced analysis of the displacement and strain fields in the specimens of both quasi-static and dynamic experiments. At least 5 specimens of the each structure were tested per one strain-rate to ensure a sufficient statistics and relevancy of the results.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Mauko, A.; Adorna, M.; Ing. Michaela Jurko; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2019, Temperature dependence of material behaviour at high strain-rate, Politecnico di Torino), ISBN 978-88-85745-27-8

Anotace:

Specimens based on re-entrant honeycomb auxetic lattice were printed from powdered austenitic steel using selective laser sintering and subjected to dynamic compression using Split Hopkinson Pressure Bar (SHPB). To study the influence of strain-rate and temperature on mechanical properties of the lattices, heating and cooling devices integrated into the SHPB apparatus were developed and the experiments were performed at two different strain rates given by different striker impact velocities. As a result, the dynamic compression was performed at two strain rates and three temperature levels (reduced, room, and elevated temperature) with 5 specimens for each combination. The specimen were observed by a pair of high-speed CMOS optical cameras and a high-speed thermal imaging camera. Optical cameras were used for evaluation of strain fields of the compressed samples using digital image correlation and for inspection of experiment validity. Thermograms were used for qualitative evaluation of heat distribution within the sample microstructure during its deformation. It has been found out that increase of strain-rate results in increase of plateau stress together with decrease of densification strain. The difference in specimen temperature led to changes in the mechanical properties, the absolute temperature of the fully compressed sample and increase of maximum measured temperature during the experiment.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2019, ISBN 978-80-01-06670-6, ISSN 2336-5382

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Jan Šleichrt, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Pithartová, K.; Senck, S.; Fürst, D.; Schrempf, A.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 28-31), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

The main goal of this study is to validate elementary mechanical parameters of a newly designed open-cell foam. The purpouse for investigating artificial material is to approach the properties of the human bone in the case of its adequate replacement. Investigated material can be also used as an artificial bone to train surgical procedures and to improve the skills of the surgeons. Four sets of the foam with different chemical composition were subjected to an uniaxial quasi-static loading to describe basic mechanical behaviour of these samples. Based on these experiments, the stress-strain diagrams were created as a comparative tool including calculation of the effective Young’s modulus. The acquired knowledges will be used as input parameters of a follow-up study aimed at describing the morphology of presented structures and their response to mechanical experiments. A distortion effect of porosity on the results is not considered in this study.

DOI:

10.14311/APP.2018.18.0028

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2018

Anotace:

The main goal of the work presented is aimed at demonstrating modern radiological methods for an investigation of the deformation behaviour of bone scaffolds. Bone scaffold is an artificial structure used for the repairs of trabecular bones damaged by injuries or degenerative diseases. In bone-tissue engineering a proper description of its deformation behaviour is one of the most important assessment characteristics of biocompatibility and bone-integration characteristics of the proposed structure intended to be used as a bone scaffold. Bioactive-glass-reinforced gellan-gum (GG-BAG) with low specific stiffness and simultaneous low attenuation to X-rays makes both the mechanical and imaging parts of the deformation experiments difficult. Therefore, a unique combination of X-ray imaging technigues and experimental procedures was developed to evaluate the full-field microstructure deformation response. The digital volumetric correlation method was applied on the reconstructed data from micro CT measurements to evaluate not only the effective mechanical characteristics but also to enable a detailed inspection of the specimens’ internal structure, particularly the deformation modes of the individual struts and joints. The calculated volumetric strain fields demonstrate the suitability of such experimental methodology and devices to assess both the microscopic and macroscopic characteristics of the investigated complex GG-BAG microarchitectures.

Typ:

Docentská habilitační práce

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.

Publikováno:

2018, The 2nd International Conference of Wave Propagation in Solids - Book of abstracts, Praha, Ústav termomechaniky AV ČR, v. v. i.), p. 43-44), ISBN 978-80-87012-67-3

Anotace:

In this contribution, an Open Hopkinson Pressure Bar (OHPB) apparatus was used for high strain-rate compression of the additively manufactured auxetic lattices and selected cellular metals. The principle of OHPB is based on Direct Impact Hopkinson Bar (DIHB). Instead of striker bar, the incident bar is accelerated in the gas-gun and it hits directly the specimen mounted on the face of the transmission bar. The incident bar is instrumented using strain-gauges and so, in contrast with Taylor anvil test, strain histories corresponding to the both contact faces of the specimen are measured and thus are known. Unlike conventional SHPB test, OHPB allows for high maximum strain in the specimen at constant strain-rate with good conditions of dynamic equilibrium as the strain waves propagate from the specimen boundaries.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 44-47), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

An experimental study on energy absorption capabilities and strain rate sensitivity of ordnance gelatine was performed. Strain energy density under quasi static compression and moderate strain rate impact tests was compared. In the study two types of material were tested, bulk ordnance gelatine and polymeric open-cell meshwork filled with ordnance gelatine. From the results a significant strain-rate effect was observed in terms of ultimate compressive strength and strain energy density. In comparison of the deformation behaviour under quasi static conditions and drop weight test the difference was very significant, however slight increase in both strength and strain energy density was observed even between different impact energies and velocities during the impact testing. The peak acceleration was significantly reduced in polymer meshwork filled by gelatine in comparison to the bulk gelatine.

DOI:

10.14311/APP.2018.18.0044

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Adorna, M.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 10-14), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

This paper presents an overview of the custom design instrumentation of a Split Hopkinson Pressure Bar modified for dynamic testing of materials with low mechanical impedance, particularly for cellular metallic materials (e. g. metal foams, laser sintered structures). Design and implementation of the components related to the strain wave measurement based on strain gauges (i.e. strain-gauge measurement unit, power supply unit, filtration) and the components used for the control and synchronization of the experiment, such as module of laser trough-beam photoelectric sensor are summarized in the paper. Aside from the design of the hardware components, the contribution deals also with development of a control software with graphical user interference using LabView (National Instruments, USA) programming environment, that allows selection of parameters of the dynamic tests and their storage for the evaluation of experiments.

DOI:

10.14311/APP.2018.18.0010

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Petr Koudelka, Ph.D.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 15-19), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

In recent years, open-source applications have replaced proprietary software in many fields. Especially open-source software tools based on Linux operating system have wide range of utilization. In terms of CNC solutions, an open-source system LinuxCNC can be used. However, the LinuxCNC control software and the graphical user interface (GUI) could be developed only on top of Hardware Abstraction Layer. Nevertheless, the LinuxCNC community provided Python Interface, which allows for controlling CNC machine using Python programming language, therefore whole control software can be developed in Python. The paper focuses on a development of a multi-process control software mainly for in-house developed loading devices operated at our institute. The software tool is based on the LinuxCNC Python Interface and Qt framework, which gives the software an ability to be modular and effectively adapted for various devices.

DOI:

10.14311/APP.2018.18.0015

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 38-43), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

The paper is focused on numerical analysis of mechanical behaviour of auxetic structures with re-entrant tetrakaidecahedral unit cell subjected to uni-axial quasi-static compression. The mechanical behaviour was evaluated inversely with respect to selected geometrical parameters of the unit cell and two different loading modes. Finite element method was used for the numerical analysis of the problem. A set of fully parametric tools has been developed, which enabled automated execution and evaluation of virtual experiments. From results of the simulations, Young’s modulus, the characteristics of the Poisson’s ratio function, and the deformation energy density were estimated. The relation between these characteristics and geometry of the unit cell, particularly the re-entrant angle and the relative density, was evaluated. Results of the numerical simulations for the unit cell and representative volume element of its three-dimensional periodic assembly are presented.

DOI:

10.14311/APP.2018.18.0038

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. et Ing. Radim Dvořák; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2018

Anotace:

Předmětem této bakalářské práce je shrnutí poznatků a faktů o šíření vlnění jednorozměrným kontinuem, zejména v dlouhých tenkých tyčích, o principech měření metodou SHPB, o technikách tvarování pulzu a okrajově i o metodách numerické mechaniky. Z teoretického úvodu vychází část praktická, kde je vytvořen zdrojový kód pro tvorbu parametrického modelu typické sestavy SHPB pro prostředí LS-DYNA. Redukovaná sestava je pak metodou konečných prvků podrobena citlivostní studii. Nakonec je provedena parametrická studie tvarovače pulzu, která sleduje vliv geometrických vlastností tvarovače na tvar napěťového pulzu a která je včetně s procesů s ní spjatých algoritmizována, čímž je umožněno snadné zpracování výsledků a případné srovnání s experimentálními daty. Primárním výstupem práce jsou výsledky parametrické studie v podobě kvantifikované míry vlivu geometrie tvarovače na změnu tvaru pulzu a automatizační algoritmy pro tvorbu modelů, provedení simulací a vyhodnocení výsledků.

Typ:

Diplomová práce

Autoři:

Adorna, M.; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 77-81), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

This work presents a data preprocessing procedure for signal acquired during high strain-rate loading using a custom Split Hopkinson Pressure Bar (SHPB). Before the evaluation of the experimental data, preprocessing of the measured signals including application of suitable digital or analog filter needs to be performed. Our department mainly focuses on measurements performed on advanced materials (e.g. materials with predefined structures or hybrid foams). For such measurements, it is essential to perform data preprocessing and apply suitable filter, to be able to appropriately determine deformation pulses on the measuring bars. This paper focuses foremost on spectral analysis of the measured signals, and design of optimal method of data filtering. Data from several different SHPB experiments were processed and results of different filtering methods are shown in this paper. Parameters of the best performing filter were optimized and shown to be universal for wide range of SHPB measurements.

DOI:

10.14311/APP.2018.18.0077

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.

Publikováno:

2018, Engineering Mechanics 2018: Book of Full Texts, Praha, Ústav teoretické a aplikované mechaniky AV ČR, v. v. i.), p. 213-216), ISBN 978-80-86246-88-8, ISSN 1805-8248

Anotace:

In this paper, a simple analytic model of Split Hopkinson Pressure Bar (SHPB) propelled by gas-gun is introduced. The model allows for prediction of the output of SHPB experiment or can be used inversely as a design tool for gas-gun propelled SHPB. The model is based on existing models of light gas-gun working according to adiabatic process and on one-dimensional wave propagation theory in linear elastic cylindrical slender bar. The model allows for calculation with elementary drag effects. Model functionality was evaluated and compared with the experimental results of a SHPB setup equipped with linear elastic (aluminium) bars and visco-elastic (polymethyl metacrylate) bars at two different impact velocities.

DOI:

10.21495/91-8-213

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Adorna, M.; Luksch, J.; Ing. Michaela Jurko; Valach, J.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2018, EPJ Web of Conferences - Volume 183 (2018) - DYMAT 2018 - 12th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, Les Ulis Cedex A, EDP Sciences - Web of Conferences), p. 1-6), ISBN 978-2-7598-9053-8, ISSN 2100-014X

Anotace:

In this paper, a split Hopkinson pressure bar (SHPB) was used for impact loading of an auxetic lattice (structure with negative Poisson’s ratio) at a given strain-rate. High strength aluminum and polymethyl methacrylate bars instrumented with foil strain-gauges were used for compression of an additively manufactured missing-rib auxetic lattice. All experiments were observed using a high-speed camera with frame-rate set to approx. 135.000 fps. High-speed images were synchronized with the strain-gauge records. Dynamic equilibrium in the specimen was analyzed and optimized pulse-shaping was introduced in the selected experiments. Longitudinal and lateral in-plane displacements and strains were evaluated using digital image correlation (DIC) technique. DIC results were compared with results obtained from strain-gauges and were found to be in good agreement. Using DIC, it was possible to analyze in-plane strain distribution in the specimens and to evaluate strain dependent Poisson’s ratio of the auxetic structure.

DOI:

10.1051/epjconf/201818302045

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Felten, M.; Fries, M.; Jung, A.

Publikováno:

2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 72-76), ISBN 978-80-01-06474-0, ISSN 2336-5382

Anotace:

In this paper Split Hopkinson pressure bar (SHPB) was used for dynamic testing of nickel coated polyurethane hybrid foams. The foams were manufactured by electrodeposition of a nickel coating on the standard open-cell polyurethane foam. High strength aluminium alloy bars instrumented with foil strain-gauges were used for dynamic loading of the specimens. Experiments were observed using a high-speed camera with frame-rate set to approx. 100.000 – 150.000 fps. Precise synchronisation of the high-speed camera and the strain-gauge record was achieved using a through-beam photoelectric sensor. Dynamic equilibrium in the specimen was achieved in all measurements. Digital image correlation technique (DIC) was used to evaluate in-plane displacements and deformations of the samples. Specimens of two different dimensions were tested to investigate the collapse of the foam structure under high-speed loading at the specific strain-rate and strain.

DOI:

10.14311/APP.2018.18.0072

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Hudák, M.

Publikováno:

2018

Anotace:

Tato bakalářská práce „Úprava SHPB pro pokročilé měření materiálů v dopravě“ realizuje dílčí prvky Dělené Hopkinsonovy tyče (z ang. Split Hopkinson Pressure Bar - SHPB) a jejich modifikaci. Účelem těchto dílčích prvků je zjednodušení obsluhy zařízení, částečné zvýšení zabezpečení a zlepšení spolehlivosti. Praktickou částí je také kompletně vypracovaná technická dokumentace, která je nezbytným podkladem pro výrobu realizovaných řešení. Funkčnost jednotlivých navržených prvků je prokázána provedenými experimenty se vzorky auxetických struktur.

Typ:

Diplomová práce

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Major, Z.

Publikováno:

2018, ISBN 978-80-01-06474-0, ISSN 2336-5382

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2018

Anotace:

The main goal of the work presented is aimed at demonstrating modern radiological methods for an investigation of the deformation behaviour of bone scaffolds. Bone scaffold is an artificial structure used for the repairs of trabecular bones damaged by injuries or degenerative diseases. In bone-tissue engineering a proper description of its deformation behaviour is one of the most important assessment characteristics of biocompatibility and bone-integration characteristics of the proposed structure intended to be used as a bone scaffold. Bioactive-glass-reinforced gellan-gum (GG-BAG) with low specific stiffness and simultaneous low attenuation to X-rays makes both the mechanical and imaging parts of the deformation experiments difficult. Therefore, a unique combination of X-ray imaging technigues and experimental procedures was developed to evaluate the full-field microstructure deformation response. The digital volumetric correlation method was applied on the reconstructed data from micro CT measurements to evaluate not only the effective mechanical characteristics but also to enable a detailed inspection of the specimens’ internal structure, particularly the deformation modes of the individual struts and joints. The calculated volumetric strain fields demonstrate the suitability of such experimental methodology and devices to assess both the microscopic and macroscopic characteristics of the investigated complex GG-BAG microarchitectures.

Typ:

Habilitační přednáška

Autoři:

Hos, J.; Ing. Nela Krčmářová; Jíra, A.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2017

Anotace:

Zkoušky určování povrchové tvrdosti představují jedny z nejpoužívanějších zkoušek materiálů. Výhodou tohoto typu testu je jeho minimální destruktivnost, nízké náklady na jeho provádění a relativně jednoduché vyhodnocení. Tato diplomová práce se zabývá vytvořením automatizované procedury měření povrchové tvrdosti porézních materiálů. Tyto poznatky jsou využity pro napsání programu pro určování nejvhodnějších lokací pro indentaci. Vstupy pro vytvořený program jsou fotografie porézního materiálů. Složením těchto snímků je vytvořen pracovní obraz na němž jsou následně prováděny procedury sloužící k identifikaci nejvhodnějších lokací pro indent. Výstupem skriptu je G-kód pro CNC proceduru. Vytvořený G-kód je použit pro experimentální měření tvrdosti. Vytvořené indenty jsou nafoceny, poté jsou změřeny velikosti jejich úhlopříček, které poslouží jako základ pro výpočet tvrdosti podle Vickerse.

Typ:

Diplomová práce

Autoři:

prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Micka, M.; Ing. Jitka Řezníčková, CSc.

Publikováno:

2017, Acta Polytechnica CTU Proceedings, 2017 (11), p. 22-30), ISSN 2336-5382

Anotace:

A comparative analysis using the programme ANSYS (FEM) deals with the generation of the computation model and with the assessment of theinfluence of the geogrids and the vertical lime-cement columnson the bearing capacity and deformation of the railway embankment in the less load- bearing subsoil. The graphic outputs give an overview of the field layout of equivalent stresses and deformation in the construction of the railway substructure.

Typ:

Článek v odborném recenzovaném periodiku cizojazyčně

Autoři:

Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 29-32), ISBN 978-80-01-06070-4, ISSN 2336-5382

Anotace:

The paper deals with investigation of deformation behaviour of gellan gum (GG) based structures prepared for regenerative medicine purposes. Investigated material was synthesized as porous spongy-like scaffold reinforced by bioactive glass (BAG) nano-particles in different concentrations. Deformation behavior was obtained employing custom designed experimental setup. This device equipped with bioreactor chamber allows to test the delivered samples under simulated physiological conditions with controlled flow and temperature. Cylindrical samples were subjected to uniaxial quasistatic loading in tension and compression. Material properties of plain GG scaffold and reinforced scaffold buffered by 50wt% and 70wt% BAG were derived from a set of tensile and compression tests. The results are represented in form of stress-strain curves calculated from the acquired force and displacement data.

DOI:

10.14311/APP.2017.7.0029

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Gantar, A; Novak, S

Publikováno:

2017, Acta Polytechnica, 57 (1), p. 14-21), ISSN 1210-2709

Anotace:

This study is focuses on an investigation of the reinforcement effect of the bioactive glass nano-particles in the gellan gum (GG) scaffolds used in bone tissue engineering. The investigated material was synthesized as the porous spongy-like structure improved by the bioactive glass (BAG) nano-particles. Cylindrical samples were subjected to a uniaxial quasi-static loading in tension and compression. Very soft nature of the material, which makes the sample susceptible to damage, required employment of a custom designed experimental device for the mechanical testing. Moreover, as the mechanical properties are significantly influenced by testing conditions the experiment was performed using dry samples and also using samples immersed in the simulated body fluid. Material properties of the pure GG scaffold and the GG-BAG reinforced scaffold were derived from a set of tensile and compression tests under dry and simulated physiological conditions. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data.

DOI:

10.14311/AP.2017.57.0014

Typ:

Článek v periodiku excerpovaném databází Scopus cizojaz.

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Felten, M.; Fries, M.; Ing. Jan Falta; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.

Publikováno:

2017, 25th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY - PROGRAM AND BOOK OF ABSTRACTS, Ljubljana, Inštitut za kovinske materiale in tehnologije), ISBN 978-961-94088-1-0

Anotace:

In this paper, a Split Hopkinson Pressure Bar (SHPB) apparatus is used for impact loading of the selected cellular metallic materials. The experimental setup is arranged as a modified Kolsky setup. The experiment is observed using a high-speed camera for assessment of in-plane displacement and strain fields in the sample using digital image correlation (DIC). The functionality of the system is demonstrated on experiments where additively manufactured metallic auxetic lattices and nickel-coated open-cell polyurethane foam were used as specimens.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2017, ISBN 978-80-01-06070-4, ISSN 2336-5382

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2017, Advanced Engineering Materials, 19 (10), ISSN 1438-1656

Anotace:

In this paper, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatine. Samples from each group are tested under quasi-static loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasi-static and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05–1.4, whereas the effect of gelatine leads to increase of only 5–10%. Analysis of the Poisson's function reveals influence of filling on achievable (negative) values of Poisson's ratio, when compared to unfilled specimens. The results for the Poisson's function yielded apparently different values as the assessed minima of quasi-static Poisson's ratio in small deformations are constrained by a factor of 15.

DOI:

10.1002/adem.201700076

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Jan Falta; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Šperl, M.

Publikováno:

2017

Anotace:

Tato práce řeší problematiku instrumentace dělené Hopkinsonovy tyče modifikované pro dynamická měření materiálů s nízkou mechanickou impedancí. Zaměřuje se na návrh a realizaci součástí souvisejících se samotným záznamem deformačních pulzů z tenzometrických snímačů (jednotka pro tenzometrická měření, napájecí jednotka, filtrace) až po součásti sloužící k řízení a synchronizaci experimentu (modul optických bran a trigger vysokorychlostní kamery). Součástí práce je také návrh softwarového řešení, s grafickým uživatelským rozhraním, umožňujícím nastavení parametrů záznamu měření, samotné zaznamenání měřených veličin a jejich uložení pro potřeby vyhodnocení experimentu. Použitelnost a spolehlivost implementovaného řešení pro rutinní experimenty instrumentovaného SHPB je potvrzena provedenými experimenty se vzorky auxetických struktur. Tyto experimenty se následně podařilo spolehlivě vyhodnotit. Výsledkem této práce je soubor technických řešení (hardwarových i softwarových) zlepšujících kvalitu a spolehlivost měřených dat a také zvyšující celkový komfort obsluhy instrumentovaného zařízení SHPB.

Typ:

Diplomová práce

Autoři:

Ing. Tomáš Fíla, Ph.D.

Publikováno:

2017

Anotace:

In this study, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatin. Samples from each group are tested under quasi-static loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasi-static and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05–1.4, whereas the effect of gelatin leads to increase of only 5-10%. Analysis of the Poisson’s function reveals influence of filling on achievable (negative) values of Poisson’s ratio, when compared to unfilled specimens. The results for the Poisson’s function yielded apparently different values as the assessed minima of quasi-static Poisson’s ratio in small deformations are constrained by a factor of 15.

Typ:

Kandidátské minimum

Autoři:

prof. Ing. Josef Jíra, CSc.

Publikováno:

2017, ISBN 978-80-01-06140-4, ISSN 2336-5382

Typ:

Sborník z fakultní konference cizojazyčně

Autoři:

Ing. Petr Koudelka, Ph.D.

Publikováno:

2017

Anotace:

The aim of the dissertation is investigation of mechanical behavior of auxetic materials using numerical modeling techniques. The studied auxetic constructs are intended to be used as a matrix in modular panels for ballistic protection and mitigation of deformation energy of blasts. Thus, the analyses will be primarily focused on development of modeling schemes for reliable prediction of the materials’ mechanical properties and their optimization in the given design domain according to required characteristics. Particular attention will be paid in the numerical studies to evaluation of influence of structural characteristics on overall mechanical characteristics including the Poisson’s function and specific absorbed deformation energy. According to analogy of the metal foams and beam-like discretization schemes of their microstructure in terms of mechanical properties, the same approach can be used for numerical modeling of auxetic structures, both produced by modification of an existing foam and auxetic constructs with directly controlled geometry. Hence, the methods developed for inverse estimation of the effective mechanical properties of metal foams will be used as a basis for development of prediction and optimization schemes for the auxetic structures. The analyses will be at first performed with structures exhibiting in-plane negative Poisson’s ratio and, only after verification of the used methods, fully 3D structures with volumetric negative Poisson’s ratio characteristics will be simulated. After verification of the quasi-static results, explicit dynamics simulations will be carried out in large deformation field and as a self-contact problem. Numerical simulations will be complemented by experimental tests at micro- and macroscale.

Typ:

Kandidátské minimum

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2017, 25th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY - PROGRAM AND BOOK OF ABSTRACTS, Ljubljana, Inštitut za kovinske materiale in tehnologije), p. 52-52), ISBN 978-961-94088-1-0

Anotace:

In this study behavior of selected types of filling material were tested in compressive loading mode at high strain rates. Four types of filling material were tested, (i) ordnance gelatin, (ii) low expan sion polyurethane foam, (iii) thixotropic polyurethane putty and (iv) silicon putty. To evaluate their contribution to the impact energy absorption in IPC bulk samples of selected materials were subjected to high strain rate compression. The high strain ra te compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was adjusted to be able to test cellular and soft materials. From the tests stress - strain diagrams of investigated materials were obtained, which provided relevant mechanical properties (plateau stress and strain, strain energy density).

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 72-75), ISBN 978-80-01-06070-4, ISSN 2336-5382

Anotace:

Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose. In this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465HV1.019 and average Vickers hardness of ALCORAS was 36.585HV1.019.

DOI:

10.14311/APP.2017.7.0072

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; doc. Ing. Petr Zlámal, Ph.D.; Kumpová, I.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Gantar, A.; Novak, S.

Publikováno:

2017, Materials and Technology, 51 (3), p. 397-402), ISSN 1580-2949

Anotace:

The presented work is aimed at a demonstration of modern radiological methods for an investigation of the deformation behaviour of bone scaffolds. Bone scaffold is an artificial structure used for the repairs of trabecular bones damaged by injuries or degenerative diseases. In bone-tissue engineering a proper description of its deformation behaviour is one of the most important characteristics for an assessment of the biocompatibility and bone-integration characteristics of the proposed structure intended to be used as a bone scaffold. According to recent studies bioactive-glass-reinforced gellan-gum (GG-BAG) is a promising material for bone-scaffold production. However, its low specific stiffness and simultaneous low attenuation to X-rays makes both the mechanical and imaging parts of the deformation experiments difficult. As a result a state-of-the-art experimental setup composed of high-precision micro-loading apparatus designed for the X-ray observation of deformation processes and an advanced radiographical device is required for such experiments. High-resolution time-lapse micro-focus X-ray computed tomography (micro CT) under loading in three different imaging modes was performed to obtain a precise structural and mechanical description of the observed deforming GG-BAG scaffolds.

DOI:

10.17222/mit.2015.237

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Adorna, M.; Fisher, C.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2017

Anotace:

Předložená práce se zabývá vyhodnocováním dynamických experimentů prováděných na instrumentovaném zařízení SHPB modifikovaném pro měření materiálů s nízkou mechanickou impedancí. V rámci práce je navržena a implementována metodika předzpracování zaznamenaných experimentálních dat, vytvořena sada softwarových nástrojů umožňující konzistentní a přesné vyhodnocení. Celé řešení je implementováno v modulárním uživatelském rozhraní, které umožňuje automatizované, rychlé a spolehlivé vyhodnocení zaznamenaných experimentálních dat. Navržené řešení je ověřeno v rámci vyhodnocení experimentů provedených na auxetické struktuře a na vzorku porézní polymerní pěny. Výsledky získané s použitím navrženého řešení jsou konzistentní a odpovídají již dříve publikovaným hodnotám. Výsledkem práce je soubor softwarových řešení implementovaný v uživatelském prostředí, který značně usnadňuje a zrychluje proces vyhodnocení experimentů provedených na SHPB.

Typ:

Diplomová práce

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Tomáš Doktor, Ph.D.; Kumpová, I.; Koudelková, V.; Nepomucká, K.; Šepitka, J.; Gantar, A.

Publikováno:

2017, 25th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY - PROGRAM AND BOOK OF ABSTRACTS, Ljubljana, Inštitut za kovinske materiale in tehnologije), ISBN 978-961-94088-1-0

Anotace:

The microtomography inspection was performed using the patented (European patent no. EP2835631) in-house designed modular radiographical imaging device equipped with scintillators, large single photon counting and spectroscopic detectors. From reconstructed volumetric data internal microarchitecture, porosity, cell-wall thickness and BAG distribution was derivated. The results were compared with the results of the planar analysis of thin scaffold layers prepared by cryosection.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Jitka Řezníčková, CSc.; doc. Ing. Jitka Jírová, CSc.

Publikováno:

2016

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2016, ISBN 978-80-01-06009-4

Typ:

Sborník z mezinárodní konf. v češtině

Autoři:

Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2016, Materials and Technology, 50 (3), p. 311-317), ISSN 1580-2949

Anotace:

In the presented paper, three types of auxetic structures were produced with direct 3D printing and their compressive mechanical properties were tested. Samples were prepared from acrylic material suitable for high-resolution direct printing. Three different structures exhibiting in-plane and volumetric negative strain-dependent Poisson's ratio were selected for the analysis: two-dimensional missing-rib cut, two-dimensional inverted (re-entrant) honeycomb and three-dimensional inverted (re-entrant) honeycomb. The samples were subjected to quasi-static compression, from which stress-strain relationships were established. For a proper strain evaluation, digital-image correlation was applied to measure full-field displacements on the sample surfaces. From the displacement fields, true strain/true stress curves were derived for each sample. Furthermore, for each structure a three-dimensional FE model was developed using beam elements and subjected to identical loading conditions. Then, experimentally obtained stress-strain relationships were compared with numerically obtained results. For all the tested auxetic structures, the compressive behaviour was predicted well by the FE models. This demonstrates that parametric FE models can be used to tune the design parameters of the structures with a negative Poisson's ratio to optimize their overall properties.

DOI:

10.17222/mit.2014.204

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Hos, J.; Ing. Jan Šleichrt, Ph.D.

Publikováno:

2016, Materials and Technology, 50 (3), p. 413-417), ISSN 1580-2949

Anotace:

Composite materials with a polymeric matrix reinforced by carbon fibres are nowadays widely used as high-tech structural materials with excellent mechanical properties (particularly their stiffness and strength). The application of this type of composite to structural parts exposed to thermal loading has recently been proposed. Such an application requires an investigation and analysis of the mechanical behaviour under long-term exposure to simultaneous thermal and mechanical loading. In this paper the measurements and results of the creep behaviour of a composite with a polyphenylene sulphide matrix reinforced with chopped poly-acrylonitrile carbon fibres (C/PPS) are presented. The measured compound is proposed for use as a structural material for a jet-engine frame in the aerospace industry and the internal parts of aircraft with possible thermal loading. A custom experimental device designed for the creep measurements of composite materials was used for measurements of the developing strain at a constant tensile stress and temperature. Short-term creep tests with continuous strain monitoring were performed at a constant stress level at several elevated temperatures below and above the glass-transition temperature of the matrix. The strain was measured using the digital image correlation (DIC) method. The measured data were processed to find the strain-to-time dependency and the creep-compliance-to-time dependency. The creep-compliance-to-time data were also fitted using Findley's creep law for polymers to evaluate the model parameters and to analyse the applicability of the model for a PPS polymer reinforced with chopped carbon fibres.

DOI:

10.17222/mit.2014.208

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2016, Materials and Technology, 50 (3), p. 301-305), ISSN 1580-2949

Anotace:

The study aims at mechanical testing of an artificial bone structure in the form of a scaffold for the application in the repairs of trabecular bones after wounds or degenerative diseases. Such artificial construct has to conform to many requirements including biocompatibility, permeability properties and bone-integration characteristics. Recently, self-degradable bone scaffolds suitable for natural-bone-tissue ingrowth optimized with respect to mechanical properties and body-fluid flow have been considered as an alternative to allografts and autografts. Here, an analysis of deformation behaviour of a scaffold with a morphology identical to the natural bone is the first step in this task. In this work, the geometry and morphology of scaffold specimens produced with direct 3D printing were based on a 3D model derived from the X-ray-computed micro-tomography measurement of a real trabecular bone. The geometrical model was upscaled four times in order to achieve the optimum ratio between its resolution and the resolution of the 3D printer. For its biocompatibility and self-degradability, polylactic acid was used as the printing material. The mechanical characteristics were obtained from a series of uniaxial compression tests, with an optical evaluation of the strain field on the surfaces of the specimens. The acquired stress-strain curves were compared with the characteristics of a real trabecular bone obtained with time-lapse microtomography measurements, evaluated with the digital volumetric correlation method. The results show good correspondence of the stiffness values for both the natural and artificial bone specimens.

DOI:

10.17222/mit.2014.190

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Adorna, M.; Ing. Michaela Jurko; Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Gantar, A; Novak, S

Publikováno:

2016, Engineering Mechanics 2015, Zurich, TRANS TECH PUBLICATIONS LTD), p. 665-670), ISSN 1662-7482

Anotace:

This work presents deformation behaviour of gellan gum and gellan gum - bioactive glass composites as novel hydrophilic materials for production of scaffolds in the field of bone-tissue engineering. According to recent studies such materials are attractive for personalized design of implants thanks to their biocompatibility and wide range of available fabrication methods. Batch of samples was subjected to uni-axial compression loading in a custom designed loading device to obtain their elastic and plastic characteristics. However the testing procedure was challenging because of very low stiffness of the material acquired results show a significant reinforcement effect of bioactive glass and its influence to the elastic modulus.

DOI:

10.4028/www.scientific.net/AMM.821.665

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Jan Šleichrt, Ph.D.; Adorna, M.; Ing. Michaela Jurko; Ing. Nela Krčmářová; Petráňová, V.

Publikováno:

2016, XIVth Youth Symposium on Experimental Solid Mechanics, Praha, ČVUT v Praze, Česká technika - nakladatelství ČVUT), p. 71-74), ISBN 978-80-01-05885-5, ISSN 2336-5382

Anotace:

This work presents deformation behaviour of cost effective chopped fiber composites. Use of chopped fibre is advantageous for manufacturing however complex shape parts production technology could be challenging. Batches of samples with different fibres composition were subjected to uni-axial tensile loading to obtain overall materials properties and inspection of proper manufacturing based on local deformation inhomogeneities. Both crossbeam displacement and optical strain measurement were used for elastic characteristics evaluation. Deformation response was derived from full-field optical strain measurements based on digital image correlation method. Relatively large variation of mechanical properties testing of samples was found.

DOI:

10.14311/APP.2016.3.0071

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2016, Engineering Mechanics 2015, Zurich, TRANS TECH PUBLICATIONS LTD), p. 428-434), ISSN 1662-7482

Anotace:

In this work parametric modelling was utilized to design and produce two types of porous microarchitectures with auxetic compressive properties suitable for deformation energy mitigation applications such as blast and bullet protection. The samples were directly produced from acrylic amaterial using a high resolution 3D printer and their compressive mechanical characteristics were tested. Two different structures exhibiting in-plane negative strain dependent Poisson’s ratio were selected for the analysis: i) two-dimensional inverted (re-entrant) honeycomb and ii) two-dimensional cut missing-rib. Stress-strain relationships were established from a set of quasi-static compressional experiments where the strain fields were evaluated using digital image correlation applied to measure the full-field displacements on the samples' surface. From the displacement fields true strain – true stress curves were derived for each sample and relative elastic moduli were evaluated.

DOI:

10.4028/www.scientific.net/AMM.821.428

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2016, Book of Abstracts of International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences 2016, Praha, katedra mechaniky a materiálů), ISBN 978-80-01-06009-4

Anotace:

This study is focused on investigation of the reinforcement effect of the nano-particles in gellan gum (GG) scaffolds used in bone tissue engineering. This hydrophilic polysaccharide-based material is attractive for personalized design of implants thanks to its biocompatibility and wide range of available fabrication methods. Material properties of pure GG scaffold and GG-BAG reinforced scaffold were derived from set of tensile and compression tests under dry and simulated physiological conditions. The results are represented in form of stress-strain curves calculated from acquired force and displacement data. It can be concluded that significant reinforcement effect of BAG was observed only during the compressive loading.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Fíla, Ph.D.; Kumpová, I.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Vavřík, D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.

Publikováno:

2016, Journal of Instrumentation, 11 (1), ISSN 1748-0221

Anotace:

In this paper, we employ dual-energy X-ray microfocus tomography (DECT) measurement to develop high-resolution finite element (FE) models that can be used for the numerical assessment of the deformation behaviour of hybrid Ni/Al foam subjected to both quasi-static and dynamic compressive loading. Cubic samples of hybrid Ni/Al open-cell foam with an edge length of [15]mm were investigated by the DECT measurement. The material was prepared using AlSi7Mg0.3 aluminium foam with a mean pore size of [0.85]mm, coated with nanocrystalline nickel (crystallite size of approx. [50]nm) to form a surface layer with a theoretical thickness of [0.075]mm. CT imaging was carried out using state-of-the-art DSCT/DECT X-ray scanner developed at Centre of Excellence Telč. The device consists of a modular orthogonal assembly of two tube-detector imaging pairs, with an independent geometry setting and shared rotational stage mounted on a complex 16-axis CNC positioning system to enable unprecedented measurement variability for highly-detailed tomographical measurements. A sample of the metal foam was simultaneously irradiated using an XWT-240-SE reflection type X-ray tube and an XWT-160-TCHR transmission type X-ray tube. An enhanced dual-source sampling strategy was used for data acquisition. X-ray images were taken using XRD1622 large area GOS scintillator flat panel detectors with an active area of [410 × 410]mm and resolution [2048 × 2048]pixels. Tomographic scanning was performed in 1,200 projections with a 0.3 degree angular step to improve the accuracy of the generated models due to the very complex microstructure and high attenuation of the investigated material. Reconstructed data was processed using a dual-energy algorithm, and was used for the development of a 3D model and voxel model of the foam. The selected parameters of the models were compared with nominal parameters of the actual foam and showed good correlation.

DOI:

10.1088/1748-0221/11/01/C01005

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Likhonina, R.; Micka, M.

Publikováno:

2016, Acta Polytechnica, 56 (6), p. 455-461), ISSN 1210-2709

Anotace:

This paper deals with a FEA simulation of the vehicle crash with steel safety barriers in ANSYS LS-DYNA® 15.0. Two types of safety barriers are used: JSNH4/H2 and JSAM-2/H2. A geometrical model of the barrier in the Modeler ANSYS® Workbench™ 15.0 was created and after that it was transformed into LS-DYNA® 15.0 to complete the crash test simulation. After computation in solver ANSYS LS-DYNA® 15.0 the results of the simulation such as impact forces, a body displacement and an integral energy were analyzed.

DOI:

10.14311/AP.2016.56.0455

Typ:

Článek v periodiku excerpovaném databází Scopus cizojaz.

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2016, Book of Abstracts of International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences 2016, Praha, katedra mechaniky a materiálů), ISBN 978-80-01-06009-4

Anotace:

This work presents deformation behaviour of cost effective chopped fiber composites. Use of chopped fibre is advantageous for manufacturing however complex shape parts production technology could be challenging. Batches of samples with different fibres composition were subjected to uni-axial tensile loading to obtain overall materials properties and inspection of proper manufacturing based on local deformation inhomogeneities. Deformation behaviour of chopped fibre composites represented by stress-strain curves and strain maps was described based on optical measurement of standard tensile test. Local strain concentrations predicting failure area was identified.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Šperl, M.

Publikováno:

2016, XIVth Youth Symposium on Experimental Solid Mechanics, Praha, ČVUT v Praze, Česká technika - nakladatelství ČVUT), p. 35-38), ISBN 978-80-01-05885-5, ISSN 2336-5382

Anotace:

In this study high resolution thermography is used for identification of damaged zones in Carbon fiber/polyphenylene sulfide (C/PPS) long fiber composite specimens with induced impact damage subjected to tensile fatigue loading. Image processing techniques were applied on thermographs from all loading cases to obtain segmented images of the damaged location that were then used for calculation of the heated area. Results show that the considered method can be used to identify heated area in the vicinity of damage with high confidence at low number of cycles where no significant fatigue effect is present in the material.

DOI:

10.14311/APP.2016.3.0035

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A; Kumpova, I

Publikováno:

2016, Journal of Instrumentation, 11 (11), p. 1-7), ISSN 1748-0221

Anotace:

Hybrid foams are materials formed by a core from a standard open cell metal foam that is during the process of electrodeposition coated by a thin layer of different nanocrystalline metals. The material properties of the base metal foam are in this way modified resulting in higher plateau stress and, more importantly, by introduction of strain-rate dependence to its deformation response. In this paper, we used time-lapse X-ray micro-tomography for the mechanical characterization of Ni/Al hybrid foams (aluminium open cell foams with nickel coating layer). To fully understand the effects of the coating layer on the material’s effective properties, we compared the compressive response of the base uncoated foam to the response of the material with coating thickness of 50 and 75 µm. Digital volume correlation (DVC) was applied to obtain volumetric strain fields of the deforming micro-structure up to the densification region of the deforming cellular structure. The analysis was performed as a compressive mechanical test with simultaneous observation using X-ray radiography and tomography. A custom design experimental device was used for compression of the foam specimens in several deformation states directly in the X-ray setup. Planar X-ray images were taken during the loading phases and a X-ray tomography was performed at the end of each loading phase (up to engineering strain 22 %). The samples were irradiated using micro-focus reflection type X-ray tube and images were taken using a large area flat panel detector. Tomography reconstructions were used for an identification of a strain distribution in the foam using digital volumetric correlation. A comparison of the deformation response of the coated and the uncoated foam in uniaxial quasi-static compression is summarized in the paper.

DOI:

10.1088/1748-0221/11/11/C11017

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Petráňová, V; Šepitka, J.; Lukeš, J.; Gantar, A; Novak, S

Publikováno:

2016, Program and book of abstracts, Ljubljana, IMT Ljubljana), ISBN 978-961-94088-0-3

Anotace:

Regeneration of human bone tissue damaged by injuries or by degenerative diseases using biodegradable bone scaffold is one of the promising alternatives to the established treatment methods. This paper is focused on monitoring of BAG particles distribution and material properties mapping employing scanning electron microscopy (SEM) observation and nanoindentation measurement.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Keršner, Z.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2016

Anotace:

Pokročilé experimentální metody v mechanice vyžadují vývoj vlastních experimentálních zařízení, jejichž nezbytnou součástí je řídicí systém. V této práci je popsán návrh a realizace modulární řídicí jednotky poskytující otevřené řešení pro ovládání experimentálních zařízení. Navržená jednotka umožňuje ovládat zařízení s polohováním pracujícím na principu krokového motoru, popř. servo-motoru včetně bezpečnostních prvků, ovládat periferie a vyčítat veličiny měřené během experimentu (signál typu mV/V). V rámci práce byly rovněž vytvořeny softwarové nástroje pro implementaci řídicí jednotky do stávajících ovládacích aplikací pracujících na principu OS Linux s real-time jádrem a jeho speciálním modulem pro řízení LinuxCNC. V závěru byl proveden pilotní experiment s instrumentovaným mikroindentorem, který potvrdil funkčnost navrženého řídicího systému.

Typ:

Diplomová práce

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2016

Anotace:

Bylo vypracováno odborné posouzení konstrukce nového železničního návěstidla s využitím analytických výpočtů dle platných norem a numerických výpočtů metodou konečných prvků.

Typ:

Výzkumná zpráva v češtině

Autoři:

doc. Ing. Vít Fábera, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Ing. Jitka Řezníčková, CSc.

Publikováno:

2016, ISBN 978-80-01-05939-5

Typ:

Sborník z lokální konf. cizojazyčně

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Hos, J.

Publikováno:

2016

Anotace:

SEM inspection, EDX analysis, hardness testing and grain structure analysis of delivered rectangular hollow structural section performed using in-house developad evaluation procedures.

Typ:

Výzkumná zpráva cizojazyčně

Autoři:

Ing. Luboš Nouzovský, Ph.D.; Ing. Martin Jacura, Ph.D.; Ing. Jan Vyčichl, Ph.D.; Ing. Michal Drábek, Ph.D.; Ing. Josef Mík, Ph.D.; doc. Ing. Jakub Kraus, Ph.D.; Ing. Martin Langr, Ph.D.

Publikováno:

2016, ISBN 978-80-01-06016-2

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Králík, V.

Publikováno:

2016, Engineering Mechanics 2015, Pfaffikon, Trans Tech Publications Inc.), p. 428-434), ISBN 978-3-03835-700-1, ISSN 1660-9336

Anotace:

Purpose of this study is investigation of energy absorption capability of the sandwich struc- tures composed of combination of polystyrene and metal foam element and their suitability as new structure for design of protective helmets. Two types of the metal foams were experimentally tested and evaluated: Alporas (Shinko Wire Ltd., Japan) and Aluhab (Aluinvent Plc., Hungary). Samples of the sandwich structure are composed of two layers: bottom expanded polystyrene (EPS 200S) layer and upper metal foam layer which are glued together. Prepared samples are tested using a drop tower experiment to measure sample response (acceleration, reaction force) at different strain rates and en- ergies. Acceleration/time history was used for the Head Injury Criterion (HIC) calculation. HIC is the significant parameter which expresses probability of head injury arising from an impact. Moreover, measured and derived characteristics are compared with pure EPS samples to obtain comparison of deformation behaviour between conventional structure for protective helmets and designed sandwich structures. Performed experimental work showed that Aluhab sandwich can be promising structure for protective helmet designs however further optimisation of the structure properties will be necessary.

DOI:

10.4028/www.scientific.net/AMM.821.420

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Major, Z; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2016, ISBN 978-80-01-05885-5, ISSN 2336-5382

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2015, Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 1-12), ISBN 978-1-905088-63-8, ISSN 1759-3433

Anotace:

This paper deals with finite element modelling of auxetic cellular structures and nu- merical optimization of their effective mechanical properties. Three different auxetic structures (two-dimensional cut missing-rib, two-dimensional inverted (re-entrant) hon- eycomb and three-dimensional inverted honeycomb) were designed and produced by additive manufacturing. Fully parametric representations of the structures are devel- oped based on their geometric design and tested in a virtual finite element experiment to uncover the relationship between the overall properties and design parameters. Deformation behaviour of the selected auxetics assessed numerically is verified against experiments in which deformation is measured precisely in a large area using digital image correlation up to large strain values. Then the strain-stress curves are compared to the numerically obtained values. In the finite element analyses the geometries of the structures have been discre- tised either with three-dimensional solid elements (eight-node hexahedral elements) and with beam elements. The numerical model was equipped with the elasto-plastic material model with a von Mises yield criteria and bilinear isotropic work hardening. To inversely calculate the stress-strain relationship of the structures for large strain values both geometric and material nonlinearities were taken into account. The effects of selected structural parameters (both geometric given e.g. by relative density, rod thickness, internal angles, etc. and material given by elastic properties of the base material) are studied using parametric finite element modelling to obtain their effects on overall mechanical properties (stiffness and strength). Auxetic structures are then optimized using design parameter driven finite element models which are able to predict various effective mechanical properties such as elastic modulus, strength and Poisson’s ratio.

DOI:

10.4203/ccp.108.153

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Adorna, M.; doc. Ing. Daniel Kytýř, Ph.D.; Šperl, M.

Publikováno:

2015

Anotace:

Předložená práce se zabývá měřením deformační odezvy kompozitních materiálů při zkoušce pevnosti v tahu a creepové zkoušce. K řešení byla použita metoda optické korelace obrazu a pole deformací byla vyhodnocována v průběhu experimentu. Byla provedena celá série těchto testů na vzorcích několika různých typů, měření bylo doplněna o tenzometrické měření. Byla vytvořena sada vyhodnocovacích scriptů ve výpočetním prostředí Matlab. Pro analytický popis průběhu tečení byl jako nejlépe odpovídající použit Findleyho model. Dále byl sledován vliv úpravy výrobní technologie a geometrie vzorků na konzistentnost naměřených dat a mechanické vlastnosti materiálu. Výsledky této práce tak ukazují možnost využití tohoto materiálu v leteckém průmyslu v méně zatěžovaných částech konstrukce.

Typ:

Diplomová práce

Autoři:

Vitteková, M.; Vašátko, J.; Ing. Jitka Řezníčková, CSc.; Král, M.

Publikováno:

2015, ISBN 978-80-214-5236-7

Typ:

Sborník z lokální konf. v češtině

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šepitka, J.; Lukeš, J.

Publikováno:

2015, Proceedings of the 11th Conference on Local Mechanical Properties, Uetikon-Zurich, Trans Tech Publications), p. 129-133), ISBN 978-3-03835-555-7, ISSN 1013-9826

Anotace:

This paper deals with evaluation of mechanical properties of human trabeculae in the interconnection area. Local changes in the trabecular connections were evaluated using both quasi-static nanoindenation and modulus mapping technique. Connecting point of two trabeculae was revealed by precise grinding and polishing. A rectangular region in the interconnection was selected and inspected by modulus mapping procedure. Moreover several quasi-static indentation measurements using cube-corner indenter were performed along distinct lamellae. The obtained elastic properties were then compared with the values of the rod-like trabeculae. The comparison does not indicate significant differences in elastic properties between the trabecular rods and interconnections.

DOI:

10.4028/www.scientific.net/KEM.662.129

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Jandejsek, I.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2015

Anotace:

Předkládaná bakalářská práce se zabývá vývojem experimentální metody pro studium deformačního chování auxetických struktur (porézních materiálů vykazujících záporné Poissonovo číslo) při kvazi-statickém zatěžování. Vzhledem k charakteru odezvy zkoumaných mikrostruktur na tlakové zatížení jsou mechanické charakteristiky odvozovány z vysoce přesného měření síly během experimentů a optického vyhodnocení deformace na povrchu vzorků s použitím metody digitální korelace obrazu (2D-DIC) se subpixelovou přesností. V práci byly zkoumány vzorky tří druhů auxetických mikrostruktur s analyticky dobře popsanou deformační odezvou a teoretickým průběhem Poissonovy funkce (závislosti Poissonova čísla na deformaci) v uspořádáních odpovídajících jak rovinnému, tak volumetrickému charakteru auxetických vlastností. Pro výrobu vzorků byl využit přímý 3D tisk metodou mnohatryskového modelování s vysokým rozlišením. Z naměřených dat byly s použitím vlastního softwarového nástroje vytvořeného v programovacím prostředí Matlab stanoveny závislosti skutečné napětí - skutečná deformace, Poissonovo číslo - skutečná deformace, poměrný Youngův modul pružnosti a hustota pohlcené deformační energie. Bylo ukázáno, že předkládaná metoda je vhodná pro studium mechanických vlastností auxetických materiálů na makroúrovni, což umožní verifikaci analytických a numerických optimalizačních procedur sloužících pro návrh auxetické mikrostruktury přizpůsobené pro konkrétní aplikaci.

Typ:

Diplomová práce

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Šepitka, J.; Lukeš, J.

Publikováno:

2015, Proceedings of the 11th Conference on Local Mechanical Properties, Uetikon-Zurich, Trans Tech Publications), p. 138-141), ISBN 978-3-03835-555-7, ISSN 1013-9826

Anotace:

Bone implants in form of artificial scaffolds manufactured from poly-lactic acid (PLA) represent an attractive alternative to traditional surgical treatments of defective bones (i.e. autografts and allografts). In this work factors influencing biocompatibility and primary stability of implants manufactured from PLA using direct 3D printing were assessed using nanoindentation. For this reason bulk sample of the PLA material and a printed object were subjected to nanomechanical measurement. Quasi-static nanoindentation was employed to identify elastic modulus and hardness distribution on surface and within volume of the samples. Moreover mechanical properties along scanning direction and interlayer characteristics were also assessed. Gradients in mechanical properties have been identified within volume of the material, within the printing layers and at contact between individual layers.

DOI:

10.4028/www.scientific.net/KEM.662.138

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Lukeš, J.; Šepitka, J.; Berg, M.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2015, ESB 2015 – Book of Extended Abstracts, Praha, České vysoké učení technické v Praze, Fakulta strojní), ISBN 978-80-01-05777-3

Anotace:

Artificial bone scaffolds represent an attractive alternative to autografts and allografts used in orthopedic repairs of bone defects. Bone and bone microstructure adapted stiffness properties to their load bearing function; hence effective elastic properties of proposed bone scaffold should be similar enough to provide bone’s primary function of human body support. As an alternative to widely used bone autografts and allografts, artificial bone scaffolds have to exhibit similar bone integration properties in terms of tissue ingrowth, to allow nutrients to pass through the bone marrow and also to preserve high rates of bone regeneration. 3D printing of polylactic acid (PLA) can be successfully used for production of porous 3D structure that mimics bone tissue. However, final scaffold needs to be inspected for potential impurities and mechanical gradients due to hot rapid manufacturing process. Nanoindentation can effectively serve as a quality control tool at microscale.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Šepitka, J.

Publikováno:

2015

Anotace:

Předložená práce se zabývá návrhem, výrobou a zprovozněním indentačního zařízení schopného indentace při nízkém zatížení metodou Vickers. Za tímto účelem byly navrženy dva způsoby zatěžování, první mód pro zatěžování konstantní silou při osazení indentoru závažím a druhý mód pro zatěžování řízené silou. Pro řízení indentačního zařízení technologií CNC byl vybrán modul LinuxCNC verze 2.6.4. Pro oba způsoby zatěžování vzniklo vlastní uživatelské rozhraní. Pro kontrolu správné funkce indentoru a vyhodnocovacích procedur bylo provedeno měření na referenční tvrdoměrné destičce. Toto měření dokázalo plnou funkčnost indentačního zařízení při nízkých zatěžovacích silách. Chyba měření byla mnohem menší, než chyba předepsaná normou.

Typ:

Diplomová práce

Autoři:

Likhonina, R.; Micka, M.

Publikováno:

2015, Výpočty konstrukcí metodou konečných prvků 2015, Praha, Ústav termomechaniky AV ČR), p. 43-44), ISBN 978-80-87012-56-7

Anotace:

Článek se zabývá numerickou simulací nárazu vozidla do ocelového svodidla v ANSYS LS-DYNA. Týká se dvou typů bezpečnostních svodidel: JSNH4/H2 a JSAM-2/H2. Geometrický model svodidla byl vytvořen v ANSYS Workbench a potom byl transformován do LS DYNA k provedení simulace crash testu. Po výpočtu v řešiči ANSYS LS DYNA byly analyzovány výsledky simulace, jako jsou nárazové sily, deformace a vnitřní energie.

Typ:

Abstrakt ve sborníku z lokální konf. česky

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2015

Anotace:

Nová koncepce nosné konstrukce světelného návěstidla byla předběžně posuzována z hlediska únosnosti pomocí FEM a analytického výpočtu podle normy, dále byla posuzována šroubová spojení a betonový základ.

Typ:

Výzkumná zpráva v češtině

Autoři:

Ing. Jaroslav Valach, Ph.D.; Cacciotti, R.; Čerňanský, M.; Kouba, Z.

Publikováno:

2015, Příspěvek technických věd k záchraně a restaurování památek, Praha, Ústav teoretické a aplikované mechaniky AV ČR, v. v. i.), p. 95-106), ISBN 978-80-86246-43-7

Anotace:

Ochrana stavebních památek vyžaduje speciální přístup s ohledem na potřeby zachování hodnoty objektů. Naneštěstí chybí systematicky utříděné a snadno dostupné poznatky o podstatě a příčinách poškození historických objektů. Tuto situaci může překonat představený systém MONDIS, který pomocí sémantických technologií popisuje poškození od jejich projevu, přes jejich příčinné souvislosti až po návrh zásahu. Jeho součástí je také mobilní aplikace umožňující provádět průzkum poškození přímo v terénu

Typ:

Kapitola v jiné knize česky

Autoři:

Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2015, Materials and Technology, 49 (4), p. 597-600), ISSN 1580-2949

Anotace:

This paper deals with an experimental study of deformation response of open-cell aluminium foams under a moderate strain-rate compressive loading. Generally, porous metals show a promising potential in energy-absorption applications. However, the low strength of open-cell metal foams is a limiting parameter for such applications. Furthermore, the strain-rate sensitivity of mechanical properties is typically observed in closed-cell metal foams. On the other hand, open-cell foams provide a better control over the morphological parameters of a cellular structure. To enhance the properties of an open-cell microstructure an aluminium open-cell foam cured with polymeric filling was comparatively tested against the deformation-energy-absorption capabilities of the šas-delivered’ foam under a moderate strain-rate compressive loading. Prismatic samples with square cross-sections were prepared from the open-cell aluminium foam and a selected set of the samples was then filled with the thixotropic polyurethane putty. The specimens were tested with quasi-static compression, using a custom drop tower at several levels of the impact energy. The drop tests were instrumented with a tri-axial accelerometer and a high-speed camera to measure the mechanical response and the strain evolution during the impact. The comparison of the quasi-static behaviour with the results of the dynamic tests showed insignificant changes in the deformation curves in the case of the šas-delivered’ open-cell foam and an increasing energy-absorption capacity in the case of the samples equipped with the polymeric filling.

DOI:

10.17222/mit.2014.195

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Drdácký, M.; Slížková, Z.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2015, ISBN 978-80-86246-43-7

Anotace:

Kniha přináší přehled vybraných výsledků nedávného mezioborového výzkumu na pracovištích Ústavu teoretické a aplikované mechaniky AV ČR, v. v. i., v moderně rozvíjené oblasti památkových věd. Památkové vědy patří mezi mladší vědecké obory, jejichž vývoj je silně ovlivněn současným bouřlivým rozvojem informačních technologií, miniaturizací a pokročilostí výrobních postupů, které jsou podmínkou aplikace metod a technik dříve pro památkovou péči nedosažitelných. Prolomení technických i ekonomických bariér umožňuje využívání nanomateriálů a nanotechnologií pro záchranu, zachování i zhodnocení památkových a dalších historických objektů.

DOI:

10.21495/49-9

Typ:

Kniha - sborník, česky

Autoři:

Vitteková, M.; Vašátko, J.; Ing. Jitka Řezníčková, CSc.; Král, M.; doc. Dr. Ing. Tomáš Brandejský

Publikováno:

2015, ISBN 978-80-214-5144-5

Typ:

Sborník z lokální konf. v češtině

Autoři:

Vitteková, M.; Vašátko, J.; Ing. Jitka Řezníčková, CSc.; Král, M.

Publikováno:

2015, ISBN 978-80-214-5231-2

Typ:

Sborník z lokální konf. v češtině

Autoři:

Jung, A.; Larcher, M.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Solomos, G.

Publikováno:

2015, 11th International Conference on the Mechanical and Physical Behaviour of Materials Under Dynamic Loading, Les Ulis, EDP Sciences), ISSN 2101-6275

Anotace:

Shock absorption often needs stiff but lightweight materials that exhibit a large kinetic energy absorption capability. Open-cell metal foams are artificial structures, which due to their plateau stress, including a strong hysteresis, can in principle absorb large amounts of energy. However, their plateau stress is too low for many applications. In this study, we use highly novel and promising Ni/Al hybrid foams which consist of standard, open-cell aluminium foams, where nanocrystalline nickel is deposited by electrodeposition as coating on the strut surface. The mechanical behaviour of cellular materials, including their behaviour under higher strain-rates, is governed by their microstructure due to the properties of the strut material, pore/strut geometry and mass distribution over the struts. Micro-inertia effects are strongly related to the microstructure. For a conclusive model, the exact real microstructure is needed. In this study a micro-focus computer tomography (μCT) system has been used for the analysis of the microstructure of the foam samples and for the development of a microstructural Finite Element (micro-FE) mesh. The microstructural FE models have been used to model the mechanical behaviour of the Ni/Al hybrid foams under dynamic loading conditions. The simulations are validated by quasi-static compression tests and dynamic split Hopkinson pressure bar tests.

DOI:

10.1051/epjconf/20159404030

Typ:

Stať ve sborníku z prestižní konf. (Scopus)

Autoři:

Vitteková, M.; Vašátko, J.; Ing. Jitka Řezníčková, CSc.; Král, M.

Publikováno:

2015, ISBN 978-80-214-5235-0

Typ:

Sborník z lokální konf. v češtině

Autoři:

Ing. Jitka Řezníčková, CSc.; Král, M.; Vašátko, J.; Vitteková, M.; prof. Ing. Josef Jíra, CSc.

Publikováno:

2015, ISBN 978-80-214-5233-6

Typ:

Sborník z lokální konf. v češtině

Autoři:

Králík, V.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2015, Engineering mechanics 2015, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 420-427), ISBN 978-80-86246-42-0, ISSN 1805-8248

Anotace:

Purpose of this study is investigation of energy absorption capability of the sandwich structures composed of combination of polystyrene and metal foam element and their suitability as new structure for design of protective helmets. Two types of the metal foams were experimentally tested and evaluated: Alporas (Shinko Wire Ltd., Japan) and Aluhab (Aluinvent Plc., Hungary). Samples of the sandwich structure are composed of two layers: bottom expanded polystyrene (EPS 200S) layer and upper metal foam layer which are glued together. Prepared samples are tested using a drop tower experiment to measure sample response (acceleration, reaction force) at different strain rates and energies. From acceleration/time history the Head Injury Criterion (HIC) is calculated as significant parameters in terms of protective helmets. Moreover, measured and derived characteristics are compared with pure EPS samples to obtain comparison of deformation behaviour between conventional structure for protective helmets and designed sandwich structures.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Tomáš Mičunek, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Michal Frydrýn, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Drahomír Schmidt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Zdeněk Svatý, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Luboš Nouzovský, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Lenková, A.; Ing. Petr Koudelka, Ph.D.; Ing. Bc. Kateřina Mičunková; Ing. Michaela Jurko; Hájková, B.; Ing. Jan Šleichrt, Ph.D.; Adorna, M.; Hos, J.; Ing. Jan Falta; Ing. Nela Krčmářová

Publikováno:

2015

Anotace:

Předmětem díla je porovnání neoriginálního náhradního dílu s originálním dílem kapoty Škoda Fabia II z pohledu bezpečnosti dopravy. Dále je předmětem díla zjištění zda neoriginální náhradní díly jednoho výrobce mají stejné mechanické vlastnosti.

Typ:

Výzkumná zpráva v češtině

Autoři:

Hos, J.; Ing. Tomáš Doktor, Ph.D.; Kostelecká, M.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2015

Anotace:

Tato bakalářská práce se zabývá určováním orientace vláken v krátkovláknových kompozitních materiálech za pomoci analýzy obrazových dat. Orientace vláken velkou měrou ovlivňuje vlastnosti kompozitních materiálů. Zatímco u dlouhovláknových kompozitů může být orientace snadno kontrolována při výrobě, v případě krátkovláknových kompozitů je takováto kontrola velice obtížná. Práce se zabývá vlastnostmi kompozitních materiálů a základní teorií z oblasti zpracování obrazů. Těchto poznatků je následně využito při tvorbě softwarového nástroje pro určení orientace vláken. Vstupem do programu jsou obrazová data pořízená elektronovým mikroskopem, výstupem jsou histogramy četností orientací jednotlivých vláken.

Typ:

Diplomová práce

Autoři:

Ing. Tomáš Fíla, Ph.D.; Kumpová, I.; Jandejsek, I.; Kloiber, M.; Tureček, D.; Vavřík, D.

Publikováno:

2015, JOURNAL OF INSTRUMENTATION, 2015 (10), ISSN 1748-0221

Anotace:

We present a novel dual-source/dual energy (DSCT/DECT) micro-tomography system including results of high-resolution DSCT reconstruction. The DSCT micro-tomography setup was designed as a multi-purpose X-ray imaging device equipped with two pairs of X-ray tubes and detectors in orthogonal arrangement with independent control of beam parameters. Both pairs (tube-detector) are mounted on a computer numerical control positioning system and can be independently set up to different geometries (e.g. with different magnification of each pair). In this work the simultaneous scanning of the object by two tube-detector pairs was used for approximately half reduction of tomography scanning time. The developed imaging procedure was applied for scanning of a wooden sample locally damaged during a semi-destructive test for assessment of wood quality. Prior to the tomography measurements the setup geometry was precisely adjusted in terms of magnification, horizontal and vertical tube-specimen-detector alignment of both pairs. DSCT measurements were carried out in sequence (2 x 90 degrees for each tube) with identical 100 mu m image resolution. It was proven that the presented experimental setup combined with appropriate control technique significantly reduces tomography scanning time of materials with complex micro-structure.

DOI:

10.1088/1748-0221/10/05/C05008

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Bc. Kateřina Mičunková; Ing. Luboš Nouzovský, Ph.D.; Ing. Jan Vyčichl, Ph.D.; Ing. Martin Jacura, Ph.D.

Publikováno:

2015, ISBN 978-80-01-05791-9

Typ:

Sborník z mezinárodní konf. v češtině

Autoři:

Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Šperl, M.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 124-127), ISBN 978-80-01-05556-4

Anotace:

Carbon-fibre composite is very popular material in aircraft industry. Application of this material is limited by low fragility and low impact resistance. In flight airplane can be initialy damaged by hailstorm or bird strikes. The vibrations of the engine and turbulence during flight can be expansion of this damage. This study testing laser profilometry to investigation post damage under cycling loading.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šperl, M.

Publikováno:

2014, Materials and Technology, 48 (5), p. 777-780), ISSN 1580-2949

Anotace:

Carbon fibre in polyphenylene sulfide composites (C/PPS) became a popular material in the aircraft industry but its fragility and low impact resistance limits its application in primary aircraft structures. This study is focused on damage propagation in the laminated composites reinforced with carbon fibres. The damage may be inflicted during the ground maintenance, by an inflight bird strike or during a flight in severe meteorological conditions (heavy storms). The initial damage was created by a drop-weight out-of-plane impact using a spherical indenter. The response of the material was analysed by monitoring the impacted zones and their propagation history. The influenced area and specimen thickness in the centres of indents were chosen as the degradation parameters. The post-impact damage propagation induced by cyclic loading was assessed using a custom-designed computer-controlled laser-profilometery device. Both the upper and lower profiles of the specimen were scanned during the interruptions of the fatigue test. Global deformation was described with an analytically determined centroidal-axis curve. Local topography changes were obtained with a subtraction of this curve. Surface-deformation maps were created and used for a demonstration of the damage propagation in the specimen.

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Hos, J.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Petráňová, V.

Publikováno:

2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 48-51), ISBN 978-80-01-05556-4

Anotace:

This paper deals with calculation of fibre orientation distribution (FOD) in fibre reinforced composite. The calculation was based on image analysis algorithm applied on image acquired by scanning electron microscope. A composite with oriented fibres was selected to be enable calibration of the algorithm by comparison of the obtained results with FOD declared by the manufacturer.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Kumpová, I.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014, Book of abstract of 7th World Congress of Biomechanics, p. 597-597)

Anotace:

Micromechanical testing at the level of individual trabeculae is fundamental for proper description of deformation behaviour of a complex bone structure. This study is focused on influence of various X-ray microradiography procedures, loading procedures and tracking algorithms on accuracy of strain evaluation of loaded human trabeculae. Displacement controlled three-point bending test in both incremental and continual loading modes were carried out. To acquire best quality images two different X-ray imaging setups were used. Large area scintillator and high resolution single photon counting silicon detector WidePix with microfocus X-rays source were employed. Different voltages and target currents were tested to obtain optimal signal to noise ratio in the radiograms. Two different methods were used for displacement tracking: i) digital image correlation (DIC) and ii) tracking of artificial markers attached to the samples. In case of DIC sample inhomogeneity allowed for displacement measurement using Lucas-Kanade tracking algorithm. Gold coated borosilicate glass micro-spheres were used as the markers for displacement tracking in the second method. Here circular Hough transform was used to locate and track the positions of the markers in the loading sequence. Linearisation of the attenuation range was employed to improve contrast in the radiograms and to increase precision of the employed tracking algorithms. Stress-strain characteristics of individual trabeculae were obtained and reduction of thickness in loaded specimens correlating with strain localization was observed.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Králík, V.; Němeček, J.; Jíra, A.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2014, 20 th International Conference Engineering Mechanics 2014, Brno, Brno University of Technology), p. 324-327), ISBN 978-80-214-4871-1, ISSN 1805-8248

Anotace:

Abstract: Aluminum foams are structural materials with excellent energy absorption capacity jointed with very low specific weight and high stiffness. Products of aluminum foams are used in a wide range of structural and functional applications (e.g. as a part of composite protection elements) due to its attractive properties. Full characterization of deformation behaviour under high-strain rate loading is required for designing these applications. The aim of this study is to compare stress-strain behaviour and energy absorption of the aluminium foam structure with conventional energy absorbing materials based on polystyrene and extruded polystyrene commonly used as protective elements. The compressive deformation behaviour of the materials was assessed under impact loading conditions using a drop tower experimental device.

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2014, 9th International Conference on Local Mechanical Properties, Zürich, Transtech Publications), p. 257-260), ISBN 978-3-03785-876-9, ISSN 1013-9826

Anotace:

The paper presents application on digital image correlation (DIC) and microindentation for investigation of plastic flow under Brinell ball indenter applied on steel specimen made of two screwed together parts. Specimens in two different material state (a) as delivered (b) annealed were investigated. This approach enables internal surface to act as the external one and to be examined by mentioned methods. Results obtained by application of DIC on scanning electron microscope (SEM) images are compared to microhardness maps and agreement is demonstrated.

DOI:

10.4028/www.scientific.net/KEM.586.257

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Králík, V.; Němeček, J.

Publikováno:

2014, Local Mechanical Properties X, Zurich, TRANS TECH PUBLICATIONS LTD), p. 39-42), ISBN 978-3-03835-062-0, ISSN 1013-9826

Anotace:

This study is focused on detection and characterisation of influenced zones in micro-scale specimens of aluminium foam after thermal and mechanical loading induced by preparation process for three-point bending test. Two cell-wall specimens were prepared from a slab of aluminium foam and influences of preparation process (machining) and thermal load on local mechanical properties were investigated using nanoindentation. Although the nanoindentation is powerful method for investigation of material properties of small zones, it can be reliably used only to obtain information about elastic properties. Due to limitation of the nanoindentation for reliable measurement of inelastic properties, plastic properties were determined using a set of indirect finite element simulations of nanoindentation tests. The procedure is based on fitting numerical results to experimentally measured force-depth curves.

DOI:

10.4028/www.scientific.net/KEM.606.39

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šepitka, J.; Lukeš, J.

Publikováno:

2014, Local Mechanical Properties X, Zurich, TRANS TECH PUBLICATIONS LTD), p. 245-248), ISBN 978-3-03835-062-0, ISSN 1013-9826

Anotace:

This study is focused on inspection of damage extent induced into C/PPS composite material by fatigue and impact loading. Initial damage to specimens was induced by drop-weight out-of-plane impact damage. Several levels of damage states (intact specimen, fatigued and impacted specimen, ruptured specimen) were inspected using modulus mapping (MM) technique. Quantification of the damage level was based on comparison of results from MM obtained in distinct locations on the specimens. Regions of interest were selected in order to determine magnitude of damage after impact and to assess remaining loading capabilities of the material. For this purpose, material maps provided information about location where matrix had been inflicted by the damage. Results show that impact loading has no measurable influence on mechanical properties of the matrix. However, gradient in mechanical properties was detected in the vicinity of crack. Results were validated using quasi-static nanoindentation and constant strain rate continuous measurement that showed depth profile of mechanical properties.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Králík, V.

Publikováno:

2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 145-150), ISBN 978-80-01-05556-4

Anotace:

The aim of this study is proper description of stress-strain behaviour of the metal foam structure Alporas under high-strain rate loading. Stress-strain response of Alporas specimens is measured during an impact test using a drop tower experiment. Strain of the specimens is evaluated by two independent approaches: i) double numerical integration of acceleration data and ii) digital image correlation technique. Thus, experimental setup is equipped with triaxial accelerometer and high speed camera. Resulting stress-strain curves are compared with behaviour of polystyrene material samples (polystyrene material is commonly used as a shock absorber) obtained from the same testing procedure and with stress-strain function determined from Alporas quasi-static compression testing.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014, XIVth Bilateral German/Czech Symposium - Experimental Methods and Numerical Simulation in Engineering Sciences, Wuppertal, Bergische Universität), p. 52-55)

Anotace:

The aim of this study is proper description of stress-strain behaviour of the metal foam structure Alporas under high-strain rate loading. Stress-strain curve of Alporas specimens is measured during an impact test using a drop tower device. Strain of the specimens is evaluated by two independent approaches: i) double numerical integration of acceleration data and ii) digital image correlation technique. Resulting stress-strain curves are compared with behaviour of polystyrene material samples and results obtained from quasi-static compression testing.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Vitteková, M.; Vašátko, J.; Ing. Jitka Řezníčková, CSc.; Král, M.

Publikováno:

2014, ISBN 978-80-214-4964-0

Typ:

Sborník z mezinárodní konf. v češtině

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; Gutermann, M.; Minster, J.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014

Anotace:

The aim of the study is to develop and validate experimental and numerical modelling techniques for the investigation of deformation behaviour of a porous material. For this purpose, a trabecular bone as biological porous material was chosen. Development of the mictrostructural model with a complex inner structure consisted of three main parts: i) identification of the material model; ii) a precise description of the inner structure; iii) validation of the resulting microstructural model. Identification of the material model was based on micro (three-point bending) and nano-mechanical (nanoindentation) testing of the single trabeculae (single trabecula is the basic building element of trabecular tissue). These tests were simulated using the finite element method and the calculated results were compared (using the least square method) to experimental obtained values. In this way the best set of the material constants for elasto-visco-plastic model with damage for single trabecula were identified. To obtain a geometrically accurate finite element model of the trabecular microstructure and suitable experimental data for model validation the time-lapse micro-computed tomography scanning of compression test was performed. The sample was placed into a loading device and subjected to incremental compressive loading and each deformation step was observed using X-ray microradiographic imaging. Radiographic data were reconstructed and a high resolution voxel model was prepared from the tomography of the undeformed state. The identified material model from nano and micro-mechanical testing was prescribed to the voxel model and the simulation of the compression test was performed to verify its reliability to predict the deformation behaviour of bone. The calculated deformation fields were compared with the corresponding deformation fields which were determined from tomographically captured load states using the digital volume correlation method.

Typ:

Disertační práce (PhD)

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014

Anotace:

Bylo provedeno posouzení nosné konstrukce světelného návěstidla na provozní zatížení.

Typ:

Výzkumná zpráva v češtině

Autoři:

Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 61-65), ISBN 978-80-01-05556-4

Anotace:

Porous metals and particularly aluminium foams are attractive materials for crash applications where constructional elements have to be able to absorb considerable amount of deformation energy while having as low weight as possible. Compressive behaviour for medium impact velocities can be experimentally assessed from a series of drop-tower impact tests instrumented with accelerometer and high-speed camera. However to predict such behaviour a proper modelling scheme has to be developed. In this paper drop-tower impact tests of Alporas aluminium foam were used for development of a material model for explicit finite element simulations of high-strain rate deformation process using LS-DYNA simulation environment. From the material models available low density foam, Fu-Chang’s foam, crushable foam and modified crushable foam models were selected for simulations using smoothed-particle hydrodynamics and solid formulations respectively. Numerical simulations were performed in order to assess constitutive parameters of these models and identify material model describing deformation behaviour of Alporas with the best accuracy.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Fíla, Ph.D.; Kumpová, I.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 32-35), ISBN 978-80-01-05556-4

Anotace:

In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several deformation steps and micro-CT scanning was carried out in each step. Reconstructed three-dimensional data of intact bone sample were used to develop 3D model of the specimen. Data from each deformation step were processed by DVC method for identification of displacement and strain fields and thus for evaluation of deformation response of human trabecular bone sample.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Růžička, M.

Publikováno:

2014, ISBN 978-80-01-05556-4

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Petr Koudelka, Ph.D.; Jandejsek, I.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Drdácký, M.; Zíma, P.Z.

Publikováno:

2014, Journal of Instrumentation (9), ISSN 1748-0221

Anotace:

In order to ensure sustainability if historic buildings their technical state has to be inspected on regular basis. Damage assessment has to be preferably carried out using non-destructive methods otherwise damage accumulation may occur during life-cycle of the constructions. According to character of detected damage appropriate intervention measures (i.e. strengthening, consolidation, etc.) have to be then efficiently applied. Among other factors significantly influencing life span of constructions weathering agents (rain, erosion, dissolution, etc.) may cause rapid degradation of mechanical properties. In this paper X-ray radiograhical imaging was used to describe fluid penetration process in porous Maastricht limestone that is commonly used for restoration purposes. The imaging was performed in custom radiography device simulating practical in-situ measurements using microtube device. This device is a modified Karsten tube capable of determining absorbed volume and its speed even on inclined surfaces. However actual fluid penetration process in terms of saturation depth/volume ratio and shape of fluid wave propagating through microstructure is indeterminable using microtube. For this purpose real-time radiography imaging of fluid saturation process was performed to investigate behaviour of fluid in the material. Furthermore X-ray computed microtomography was performed to develop finite element model for simulation of fluid flow in the porous microstructure. Using the real-time imaging relations between penetration speed, penetration depth and penetrated volume were assessed. These results can be used to validate results from microtube measurements including nonlinear regions present when semi-spherical wave propagates through the material. Using a set of finite element simulations of the microtube experiment fluid velocity distribution in the material together with effective Darcy's flux were calculated and results were compared to those from real-time imaging.

DOI:

10.1088/1748-0221/9/05/C05040

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Vitteková, M.; Vašátko, J.; Ing. Jitka Řezníčková, CSc.; Král, J.

Publikováno:

2014, ISBN 978-80-214-5231-2

Typ:

Sborník z lokální konf. v češtině

Autoři:

Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014

Anotace:

The present study is focused on the investigation of mechanical behaviour of cellular materials at higher strain rates and optimisation of the material to enhance the energy absorption capabilities. The study encounters micromechanical testing, time-lapse tomography under compressive loading and moderate strain-rate loading using drop tower. Three types of material are investigated, open- and closed-cell aluminium foam and interpenetrating phase composite (IPC). The results show increase in strain energy density absorbed by IPC.

Typ:

Kandidátské minimum

Autoři:

Machek, V.; Tatíček, F.; Kubelka, M.

Publikováno:

2014, Technological Forum 2014, Jaroměř, Ing. Jan Kudláček), p. 199-201), ISBN 978-80-87583-10-4

Anotace:

The article describes the apportionment, characteristics and uses of metallic glasses.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Kumpová, I.

Publikováno:

2014, XIVth Bilateral German/Czech Symposium - Experimental Methods and Numerical Simulation in Engineering Sciences, Wuppertal, Bergische Universität), p. 66-69)

Anotace:

Deeper understanding of the relationship between morphology, micro-mechanical properties at the bone tissue level and overall mechanical properties of the bone is important for assessment of bone physiological and pathological behaviour. Modern radiological methods (e.g. computed micro-tomography) are powerful instruments for investigation of the internal structure. Using the time-lapse tomography enabled assessment of deformation response to the applied loading and monitoring of damage propagation. Different custom based set-ups of high resolution micro-focus X-ray computed tomography equipped with scintillator or single-photon counting detector were used for imaging at both meso and micro levels.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jandejsek, I.

Publikováno:

2014, 9th International Conference on Local Mechanical Properties, Zürich, Transtech Publications), p. 265-269), ISBN 978-3-03785-876-9, ISSN 1013-9826

Anotace:

The aim of this study is to determine constitutive constants for elasto-plastic material model with damage for single trabecula based on the indirect simulation of micromechanical testing and its verification at macro level using compression test of the cylindrical sample of the trabecular tissue. Three-point bending test of isolated trabeculae was performed in a shielding box and deflection of the sample was acquired using X-ray microradiography. Measured values (displacements of markers) were used for indirect identification of the material model for single trabecula using finite element (FE) method. The bending test was simulated and results were fitted to experimentally obtained values and the appropriate set of material constants was determined. To verify the applicability of the identified material model the compression test of the complex sample was carried out. Cylindrical sample was incrementally loaded and each loading state was captured using the micro-computed tomography. Material model identified from three-point bending test was applied to the model of complex sample and the simulation of the compression test was performed.

DOI:

10.4028/www.scientific.net/KEM.586.265

Typ:

Stať ve sborníku z prestižní konf.

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2014

Anotace:

Pro firmu SKODA Transportation byl zpracován posudek k provedeným zkouškám střadačových brzd dodaných společností ŠKODA TRANSPORTATION a.s. ve formě Obdorného komentáře k jednotlivým provedeným zkouškám, např. měření rozměrů, tvrdosti a drsnosti povrchů jednotlivých dílů střadačové brzdy.

Typ:

Výzkumná zpráva v češtině

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)

Anotace:

Evaluation of natural frequencies‘ shift during thermal loading of carbon fibre/polyphenylene sulphide (C/PPS) composites used in aircraft industry is described in this paper. Values of natural frequencies were chosen as indicators of changes in material properties. Custom-designed experimental device suitable for determination of specimen's natural frequencies was developed according to operation in thermal chamber. During the experiment steel pellets were dropped on specimen. Overall acoustic response of the impact was recorded by microphone. Two characteristic natural frequencies were evaluated using spectral analysis of recorded sound. Series of measurements at different temperatures were performed nearly up to the temperature of PPS glass-transition. Obtained results show strong correlation between natural frequency shift and temperature of the specimen’s surface.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.

Publikováno:

2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)

Anotace:

Presented article is focused on plastic strain distribution assessed by microindentation technique. If the nature of the specimen is unsuitable for radiological inspection destructive sample preparation is inevitable to describe its inner state. Two mutually perpendicular planes in deformed zone were manufactured by electrical discharge machining and polishing. One of the planes was created prior the loading procedure and during the loading the parts were connected by screws. In the perpendicular plane the specimen was cut after the loading. Specimens prepared using this procedure were then subjected to microindentation testing. Each set of indents consisted of approximately 150 Vickers microindents covering area of 0.5 mm2. Images of imprint arrays on the specimens surface were acquired by scanning electron microscope. Diagonals of indents were determined and then Vickers hardness values were calculated. Map of hardness distribution was created using cubic interpolation method.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2013, UPB Scientific Bulletin, Series D: Mechanical Engineering, 75 (1), p. 161-170), ISSN 1454-2358

Anotace:

During the last decades, there has been much effort on the determination of effective elastic properties of porous metals. In this paper, the overall elastic moduli of reference aluminium foam Alporas are assessed using predictive methods based on definition of compliance contribution tensor. Surface of the foam is captured using flatbed scanner and such data is subjected to image and signal processing routines in order to obtain dimensions of the sufficient representative volume element and calculation of structural characteristics for analytical homogenization. It is shown that from all considered homogenization models only the Mori-Tanaka scheme gives results reasonably close to nominal values.

Typ:

Článek v periodiku excerpovaném databází Scopus

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šperl, M.

Publikováno:

2013, UPB Scientific Bulletin, Series D: Mechanical Engineering, 75 (2), p. 157-164), ISSN 1454-2358

Anotace:

Carbon fibre in polyphenylene sulfide composites became popular ma- terial in aircraft industry but its fragility and low resistance against impact load- ing limits the application of these composites in aircraft primary structures. The article deals with experimental investigation of the mechanical response of dam- aged composite. Material degradation of intact and damaged specimens during fatigue tests was investigated. The changes in natural frequencies, ultrasound wave propagation and bending stiffness were chosen as damage parameters. The entire fatigue life of intact and damaged specimens was studied in the article by all the presented methods. The accuracy and reliability of assessment of damage parameters were compared. Comparison of accuracy and reliability of presented method for assessment of damage parameters is also given.

Typ:

Článek v periodiku excerpovaném databází Scopus

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)

Anotace:

This paper is focused on evaluation of the micro‐scale tests of isolated cell‐walls of aluminium foam. To derive mechanical properties at the level of single cells, three point bending tests were carried out. There are several ways to obtain mechanical properties from the measured data (i) manufacturing of prismatic beam, (ii) testing of a curved beam and simplification of the beam shape by an equation of a curve, (iii) indirect determination of mechanical properties using inverse finite element analysis (FEA). Due to the dimensions and complex shape of the cells there is a high risk of plastic deformation caused by specimen preparation as well as very low dimensions of resulting sample. Hence testing of a curved specimen was performed with a special attention paid to the specimen preparation. A volumetric model enabling utilization of inverse FEA was developed.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Šudřich, M.

Publikováno:

2013

Anotace:

Ochranné cyklistické přilby a jejich ochranná funkce se zkouší na základě normy ČSN EN 13087 a to pádovou zkouškou. V této práci jsem provedl experimentální měření cyklistické přilby během pádové zkoušky. Součástí práce jsou doporučení pro přípravu vzorku a experimentu. Získaná data z pádové zkoušky jsem zpracoval a následně analyzoval. Z výsledných hodnot zrychlení jsem stanovil HIC faktor, který reprezentuje ochranné vlastnosti přilby. Uvedená experimentální data jsem dále porovnal s daty, která byla získána numerickou analýzou v mojí bakalářské práci.

Typ:

Diplomová práce

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2013, Acta Technica CSAV, 58 (2), p. 157-171), ISSN 0001-7043

Anotace:

The aim of the paper is to develop a procedure for determination of elasto-visco-plastic constitutive model with damage for human single trabecula. The procedure is suited for indirect establishing of material model based on nanoindentation and three-point bending test. Constants of the material model are identified by Finite Element (FE) simulations and curve fitting using an algorithm based on least squares fitting of the experimental curves. In the case of nanoindentation, the penetration depth of tip during the FE analyses (FEA) is fitted to experimental nanoindentation curves. In the case of three-point bending, displacements of nodes are compared with displacements of markers observed during the experiment using digital image correlation.

Typ:

Článek v periodiku excerpovaném databází Scopus cizojaz.

Autoři:

Ing. Jaroslav Valach, Ph.D.; Žďárský, M.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2013, Proceedings of 30th Danubia - Adria Symposium on Advances in Experimental Mechanics, Zagreb, Croatian Society of Mechanics), p. 43-44), ISBN 978-953-7539-17-7

Anotace:

In this paper, application of laser profilometry is demonstrated for surface geometry measurement and compared to results obtained by active thermography as a reference method for damage detection and assessment. Specimens made of eight-ply carbon fiber reinforced PPS matrix laminate in the form of strips 25mm wide, 250mm long and 2mm thick were subjected to simulated impact damage. Both mothods are capable to detect impacts, which is first sign of incurred damage of material. Therefore this methods are suitable for monitoring of damage accumulation during fatigue process.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Popl, J.; Ing. Jan Vyčichl, Ph.D.; Micka, M.; doc. Ing. Jitka Jírová, CSc.

Publikováno:

2013, 20th Anniversary of the Faculty of Transportation Sciences, Czech Technical University in Prague - Selected Papers, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 298-309), ISBN 978-80-01-05320-1

Anotace:

The work deals with the simulation of the motorcycle helmet drop test with the numerical software LS-Dyna. The aim of study was to obtain acceleration values of the headform gravity center. The factors of head injuries HIC were determined from the acceleration values. The model of motorcycle helmets was created by using of a 3D handheld scanner. An impact pad was created and the headform model was modified. The draft for the model was represented by a real motorcycle helmet. Properties of materials used for making the actual helmet were assigned to the motorcycle helmet model. The quality of helmets is assessed in terms of damping properties at the drop test. Damping properties were assessed on the basis of the acceleration values of the head gravity center. A drop test was also performed on the pads rotated in different directions. The problems of motorcycle helmets testing in Europe is adjusted by the ECE 22-05 standard. The standard primarily determines how to make drop tests.

Typ:

Stať ve sborníku z fakultní konference cizojazyčně

Autoři:

Volf, T.; Ing. Jan Vyčichl, Ph.D.

Publikováno:

2013, 21th SVSFEM ANSYS Users' Group Meeting and Conference 2013, Brno, SVS FEM), p. 183-190), ISBN 978-80-905525-0-0

Anotace:

This work is focused on the elastic fastening rail to the sleeper, the definitions of used types, their usage in the Czech republic, main advantages and disadvantages, the comparison of the most popular systems on the SZDC site and the summary of the requirements for the fastening. The practical part of the work is focused on the creation on a model in the ANSYS Workbench software. There are four simulations of the load, which correspond with the real situations. The results from each situation have been analyzated (the equivalent stress, the total deformation) and have been compared among themselves. The other parts of the rail truck were analysed too.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Micka, M.; Pajkrt, J.; doc. Ing. Drahomír Schmidt, Ph.D.

Publikováno:

2013, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-57-7, ISSN 1759-3433

Anotace:

This paper describes numerical analysis, using the programme ANSYS, for the generation of the computation model and the assessment of the influence of the geosynthetic grid and the vertical lime-cement columns on the bearing capacity and the deformation of a railway embankment on a low load-bearing subsoil. The stiffening grid is located on the interface between the embankment and the subsoil. The subsoil is also reinforced by the vertical lime-cement columns. There reinforcing effect on the behaviour of the soil construction is analysed with different types of reinforcement layers. The results of the computational modelling show that the reinforcement of the railway embankment has a favourable effect on the bearing capacity of the subgrade. The graphic outputs give a clear overview of the field layout of the equivalent stresses and the deformation during the construction of the railway substructure. A comparative analysis shows that the reinforcement of the embankment, especially the columns is important mainly for poor soils in the railway embankment, i.e. for soils with poorer material characteristics and low bearing capacity.

DOI:

10.4203/ccp.102.29

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Vít Malinovský, Ph.D.

Publikováno:

2013, 20th Anniversary of the Faculty of Transportation Sciences, Czech Technical University in Prague - Selected Papers, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 294-297), ISBN 978-80-01-05320-1

Anotace:

In the on-coming years and decades the European Union is going to face in the freight sector the challenges to ensure and increase economic growth and to cope with an increase of freight transport demand and limited transport infrastructure, while at the same time the transport system should become sustainable. The freight sector has had and will continue to have very strong growth rates in the latest decades and this development is generally not considered as being sustainable. The following article is going to deal with the problems of “sustainable development” as well as main conflicts with freight transport. The author was involved at the FreightVision project that had dealt with the mentioned problems.

Typ:

Stať ve sborníku z fakultní konference cizojazyčně

Autoři:

Žďárský, M.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Šperl, M.; Ing. Tomáš Fíla, Ph.D.

Publikováno:

2013, Proceedings of 12th International Workshop on Advanced Infrared Technology and Applications, Politecnico di Torino), p. 217-219)

Anotace:

The presented work summarizes first results on hi-speed thermography analysis of cyclic loading of carbon fibers reinforced thermoplastic matrix composite. Opportunity to record and analyze minute changes of temperature is shown as well as detailed documentation of energy dumping on gradual increase of mean temperature of the specimen. Demonstrated sensitivity of the thermoanalysis is prerequisite for future investigation of impact damage as discussed in conclusions.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2013, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-57-7, ISSN 1759-3433

Anotace:

This paper describes the determination of the elasto-plastic properties of base material of aluminium foam Alporas. Three point bending experiments at the micro-scale level in conjunction with inverse finite element simulation were performed. In the cellular structure cell-walls with planar shape were identified and vicinity of such walls was extracted. Harvestedmaterial was embedded into transparent rosin to avoid plastic deformation during the manipulation and the selected wall was extracted. The specimens were finalized by grinding and polishing to achieve approximately rectangular shape. Three projections were acquired using a scanning electron microscope (SEM) and a volumetric model of the samples was developed using a semiautomatic image processing tool. Amicro-scale three-point bending test of semi-prismatic specimens extracted from the cell-wall was performed using a custom designed loading device. Loading was provided using a preloaded lead screw with precise travel. Applied force was measured using a high-accuracy load cell with a loading capacity of 2.25N. Strains were measured optically using the digital image correlation method. The volumetric model developed from the set of SEM projections was discretised using tetrahedral elements with quadratic shape functions. In the simulated bending test the elasto-plastic material model with the von Misses yield criterion and bilinear isotropic hardening was used. Boundary conditions consistent with the experimental oneswere prescribed in the simulation. Themeasured force was sampled at 50Hz and applied to the finite elementmodel. Based on themeasured displacements, parameters of the material model were varied to obtain a best fit to the experimental data (load- deflection curve). Elastic and plasticmaterial constants of the constitutivemodel were identified: (i) Young’smodulus of elasticity, (ii) yield stress and (iii) tangentmodulus.

DOI:

10.4203/ccp.102.104

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Popl, J.; Ing. Jan Vyčichl, Ph.D.; Micka, M.; doc. Ing. Jitka Jírová, CSc.

Publikováno:

2013, 21th SVSFEM ANSYS Users' Group Meeting and Conference 2013, Brno, SVS FEM), p. 133-141), ISBN 978-80-905525-0-0

Anotace:

The aim of this work was to develop a numerical model of motorcycle helmet simulating the impact of motorcycle helmet to the planar surce at different angles. A 3D handheld scanner was created to obtain the geometrical model of motorcycle helmet. The MKP model was created from the geometric model in ANSYS ICEM CFD. Material properties to this model were assigned in the LS-PrePost. Simulation of drop test was realised in LS-DYNA solver. The problems of motorcycle helmets testing in Europe is adjusted by the ECE 22-05 standard. The standard primarily determines how to make drop tests.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Jan Vyčichl, Ph.D.; Krupička, O.; Šudřich, M.

Publikováno:

2013, 21th SVSFEM ANSYS Users' Group Meeting and Conference 2013, Brno, SVS FEM), p. 191-198), ISBN 978-80-905525-0-0

Anotace:

The main aim of this study is to obtain a new virtual model of a bicycle helmet, using reverse engineering. The real bicycle helmet was transferred to the virtual model using 3D scanning equipment. The virtual surface model was subsequently modified in several software products, which supports application of reverse engineering. Using multiple editing software aims to determine the most appropriate option obtaining accurate computer models for the future. The resulting model will be applied to optimize the drop test in LS-DYNA. The numerical calculation will be compared with the measured data obtained from the real tests.

Typ:

Stať ve sborníku z mezinár. konf. česky

Autoři:

Krupička, O.; Šudřich, M.; Ing. Jan Vyčichl, Ph.D.

Publikováno:

2012, Engineering Mechanics 2012, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 192-193), ISBN 978-80-86246-39-0

Anotace:

The study focused on helmet drop tests conducted in numerical software LS-DYNA. For this purpose new virtual models of the test-head according to ČSN EN 960 (2007) and impact pad were created. A modified model of a bicycle helmet, utilized in earlier studies and obtained from 3D scan of a real bicycle helmet, was also used. The models had similar properties as a real drop test has. The aim was to find out the output value of the model head acceleration during impact and determination of Head Injury Criterion.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Minster, J.; Kostelecká, M.

Publikováno:

2012, Chemické listy, 106 (s3), p. 399-400), ISSN 0009-2770

Anotace:

The article deals with monitoring of degradation of carbon fibre reinforced polymer (CFRP) under cyclic loading. The investigated material is composed of polyphenylensulfid matrix and carbon fibres. Four specimens were subjected to repeated cyclic loading. During the fatigue loading surface of tested specimens was observed by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) to obtain surface roughness characteristics and micrographs of surface morphology. With increasing number of cycles the measured surface characteristics showed increasing surface roughness indicating at the level of micromechanics detachment of matrix from the fibers and also changes in the matrix structure itself.

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Fíla, Ph.D.; Urushadze, S.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šperl, M.

Publikováno:

2012, Engineering Mechanics 2012, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 231-237), ISBN 978-80-86246-39-0

Anotace:

Assessment of degradation rate of material can be carried out by many experimental techniques differing in complexity and sophistication. A relatively simple method based on acoustic analysis is described in this contribution. Degradation of material's properties due to fatigue loading is detectable in decrease of their modulus of elasticity that can be derived from natural frequencies of specimens, which were acquired by the presented method. These measurements utilize self-designed device capable of specimen excitation and acquisition of its vibration. The recorded signal is then processed by spectral analysis enabling determination of natural frequencies. Usefulness of the above mentioned acoustic method can be seen in the fact that the measured changes of material's parameters are comparable to those obtained by laser vibrometry, which is by several orders more expensive technique.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Jaroslav Valach, Ph.D.; Žďárský, M.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šperl, M.

Publikováno:

2012, Chemické listy, 106 (S3), p. 551-554), ISSN 0009-2770

Anotace:

The paper presents enhanced method for study of severe plastic deformation by hardness mapping utilizing portable hardness tester, flatbed scanner and software processing tool. This technique can be advantageous in situations, where crude information is not only sufficient, but also preferred, especially when it concerns testing on-site and on medium to large scale specimens and construction. Validity of the approach is supported by a comparison of hardness mapping results to the results obtained by an independent method based on evaluation of plastic strains from thermograms. It is shown that both methods determined similar shape and the extent of the plastic zone of the studied specimens.

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 88-91), ISBN 978-1-63439-432-1

Anotace:

This paper deals with development of the volume model of irregular specimens using optical projections. A s equence of 360 projections of the specimen was acquired and processed using a custom set of procedures developed in MatLab environment. The projections were segmented, filtered and smoothed. A semiautomatic procedure was used to calibrate scale of the projections and to remove eccentricity of axis of rotation of the specimen. The volume model was obtained using inverse Radon transform. Additional procedures were developed to o btain cross- section characteristics required for e valuation of corresponding micromechanical test. For verification of the developed procedure volume models of known shaped objects were estimated and compared.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Minster, J.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2012

Anotace:

Tato práce se zabývá nedestruktivním testováním uhlíkového kompozitu s polymerní matricí C/PPS. Za tímto účelem byla zvolena metoda určování degradace materiálu pomocí akustických charakteristik. Tato metoda byla významně upravena, bylo zkonstruováno vlastní experimentální zařízení a vyvinut vlastní software pro měření a vyhodnocování dat. Pomocí těchto nástrojů byly evaluovány vlastní frekvence vzorku a jejich logaritmický dekrement útlumu. Měřené změny těchto veličin byly následně použity jako indikátory poškození materiálu únavovou degradací.

Typ:

Diplomová práce

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 244-250), ISBN 978-1-63439-432-1

Anotace:

During the last decades, there has been much effort on the determination of effective elastic properties of porous metals. In this paper, the overall elastic moduli of reference aluminium foam Alporas are assessed using predictive methods based on definition of compliance contribution tensor. Surface of the foam is captured using flatbed scanner and such data are subjected to image and signal processing routines in order to obtain dimensions of the sufficient representative volume element and calculation of structural characteristics for analytical homogenization. It is shown that only the Mori-Tanaka scheme gives results close to nominal values.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Petr Koudelka, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Němeček, J.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2012

Anotace:

Thesis is aimed at the determination of effective mechanical properties of foam materials with concentration on metal foams. Elastic constants are investigated using numerical homogenization method. As a input data, 2-D macrostructure of the reference foam Alporas captured by high resolution flatbed scanner was used. The acquired image is segmented to binary one that is subjected to spectral analysis in order to assess dimensions of the representative volume element sufficient for characterization of the random microstructure of the foam. The real form of the microstructure is substituted by equivalent Voronoi diagram that is consequently transformed to finite element model. The model is used in a set of simulated mechanical tests in ANSYS software leading to determination of searched elastic constants. Obtained results are compared with the experimental ones assessed using tension test performed with the Alporas specimen.

Typ:

Diplomová práce

Autoři:

Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 92-95), ISBN 978-1-63439-432-1

Anotace:

Abstract: This paper deals with investigation of acoustic material degradation indicator (natural frequency) of carbon fibre C/PPS composite obtained by a custom-built experimental device. The specimen's sound was emitted during the impact of steel pellet in acoustic measurement experimental device. Acoustic signals were recorded and analyzed using spectral and regression analysis. Specimens were repetitively measured after designated number of loading cycles. The decreases of natural frequencies were determined for given number of natural modes. Relations between natural frequency values and their decreases were investigated. To conclude, the data assessed using acoustic measurements are suitable for evaluation of material degradation.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Žďárský, M.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2012, e-Journal of NDT, 17 (10), ISSN 1435-4934

Anotace:

In this paper the application of quantitative thermography analysis on strains is presented on the study dealing with evaluation of material's behavior during plastic deformation of specimen in two thermodynamically different states. The analysis of plastic deformation and thermal phenomena processes is demonstrated on compact-tension steel specimens both in theoretical and experimental way. The experiments proved different temperature response to external loading and dependence of plastic deformation development on material's state. These results support claim that thermography can be used for non-destructive investigation of internal state of materials.

Typ:

Článek v odborném recenzovaném periodiku

Autoři:

Jiroušek, O.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2012, ISBN 978-80-01-05062-0

Typ:

Sborník z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 31-34), ISBN 978-80-01-05062-0

Anotace:

This paper deals with evaluation of hardness fields using Vickers indentation device and a semi-automatic software tool for local hardness distribution mapping. Specimens from low carbon pipeline steels were investigated. Dense grids of Vickers imprints were created on the specimens' surface. Image data of the surface were acquired by a high resolution flatbed scanner with resolution 6400dpi. The imprints were measured using an custom-developed image processing tool, and from the obtained geometrical characteristics local hardness values were derived. From the local hardness values and their coordinates the hardness field in the whole specimen was interpolated.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Králík, V.

Publikováno:

2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 107-110), ISBN 978-80-01-05062-0

Anotace:

The aim of this study is to determine elasto-visco-plastic material model with damage for two basic structure elements of diferent porous materials: (i) human single trabecula and (ii) wall of Alporas metal foam. Indirect identification of constants of the material model is based on the numerical simulations of the nanoindentation test using custom-built optimization algorithm. During the optimization procedure the numerical results are fitted to the experimentally obtained nanoindentation curves and the best set of the constants is determined using the least squares method. For evaluation of the influence of the individual material constants a sensitivity study is performed.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2012, Engineering Mechanics 2012, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 1611-1620), ISBN 978-80-86246-40-6

Anotace:

The aim of the paper is to develop a procedure for determination of elasto-visco-plastic constitutive model with damage for human single trabecula. The procedure is suited for indirect establishing of material model based on nanoindentation and three-point bending test. Constants of the material model are identified by Finite Element (FE) simulations and curve fitting using an algorithm based on least squares fitting of the experimental curves. In the case of nanoindentation, the penetration depth of tip during the FE analyses (FEA) is fitted to experimental nanoindentation curves. In the case of three-point bending, displacements of nodes are compared with displacements of markers observed during the experiment using digital image correlation.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Fíla, Ph.D.; Urushadze, S.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šperl, M.

Publikováno:

2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 35-38), ISBN 978-80-01-05062-0

Anotace:

This paper deals with investigation of acoustic material degradation indicator (attenuation decrement drop of selected natural frequency) measured by a custom-built experimental device. Samples of C/PPS fibre composite material were analyzed. Acoustic signals were recorded and processed using spectral analysis and sound signal regression. Data measured by this method were verified by comparative experiment. Specimens were simultaneously measured using both acoustic experimental device and laser vibrometer. Modal analysis of the specimen were carried out prior to the experiment. This enabled assessment of specimens natural modes and therefore the best impact zone. In total, 10 measurements were performed for each specimen at the same level of degradation. Measured data were then processed and compared. The specimens were repetitively measured after designated number of loading cycles. To conclude, the data assessed using acoustic measurements are comparable in terms of precision, reproducibility and reliability with results from laser vibrometer and the method is suitable for evaluation of material degradation.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 263-266), ISBN 978-1-63439-432-1

Anotace:

From a mechanical point of view the most important ability of metal foam is absorption of large amounts of strain energy. This advantage is based on the cellular structure with high ratio of porosity (75-95%). The aim of this study is determination of stress-strain measurement protocol for closed-cell aluminium metal foam Alporas during a compression test using in-house loading device. Changes in structure were observed and strain was calculated based on Digital Image Correlation (DIC) technique. For the assessment of overall compression elastic modulus a new software tool based on the Matlab toolkit was developed.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Šudřich, M.; Krupička, O.; Ing. Jan Vyčichl, Ph.D.

Publikováno:

2012, 20th SVSFEM ANSYS Users' Group Meeting and Conference 2012, Brno, SVS FEM), p. 1-7), ISBN 978-80-260-2722-5

Anotace:

The protective function of a bicycle helmet is tested under ČSN EN 960 in a so-called drop test. The study is focused on helmet drop tests conducted in numerical software LS DYNA. According to this standard ČSN EN 960 - virtual model of the head and impact pad was created. The model of the bicycle helmet utilized from earlier studies and obtained from 3D scan of the real helmet was also used. The model has similar properties as a real drop test model. The quality of helmet's damping properties is derived from the values of acceleration measured in the centre of gravity of a dummy head. With the help of the LS DYNA program the quality of damping properties of three types of helmet design was compared. The effect of helmet's displacement from the ideal position on dummy head was also examined. The aim was to find the output value of the model of head acceleration during the drop test and evaluation of Head Injury Criterion. This project was done within the framework of the institutional research plan, identification code MSM6840770043.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2012, Journal of Biomechanics, 45 (S1), p. 479-479), ISSN 0021-9290

Anotace:

The single trabecula is basic beam-shaped element of bone structure. To improve knowledge of deformation behaviour of cancellous bone a mechanical tests at the level of single trabecula were performed. Elasto-plastic material properties (Young's modulus and yield point) of single trabecula, assumed as an isotropic material, were assessed from three-point bending tests. Three-point bending test was simulated using Finite Element (FE) analyses and results were compared with experimental ones for determination of suitable material model for single trabecula.

DOI:

10.1016/S0021-9290(12)70480-3

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Minster, J.; Micka, M.

Publikováno:

2012, Journal of Materials Science and Engineering (A & B), 2 (1), p. 81-89), ISSN 2161-6221

Anotace:

The aim of the paper is to find a practical numerical approach to define the time-dependent mechanical characteristics of a rheonomic material from microindentation data. The ANSYS FEM program for viscoelastic bodies is used for numerical simulations of the indentation process. All three parts of the indentation process (loading), dwell time with indentation creep and unloading, are well modelled and the histories of the relaxation modulus, the bulk or shear moduli are defined in the form of Prony series. The results obtained by numerical simulation are compared with satisfactory accuracy to the values from an analytical approach based on the linear theory of viscoelasticity and to results of standard macro tests of the material, which had been previously measured by the authors.

Typ:

Článek v odborném recenzovaném periodiku

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2012, Chemické listy, 106 (S3), p. 572-573), ISSN 0009-2770

Anotace:

In this study a novel micromechanical device has been developed. Precision of the setup has been evaluated using specimens of known material properties. Applied force was measured with capacity load sensor and the strains were measured optically. Samples of trabeculae were harvested from human proximal femur. A FE model of trabecula was developed and three-point bending test was simulated. From displacements of markers, strain values were computed. Resulting displacements of markers from FEA were fitted to experimentally obtained ones and set of parameters of the material model was determined.

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Kunášek, V.; Ing. Jan Vyčichl, Ph.D.; Micka, M.; doc. Ing. Jitka Jírová, CSc.

Publikováno:

2012, 20th SVSFEM ANSYS Users' Group Meeting and Conference 2012, Brno, SVS FEM), p. 1-8), ISBN 978-80-260-2722-5

Anotace:

The aim of this project is a numerical stress analysis of fractured human thighbone with internal osteosynthesis. We simulated incidents, when a pacient's broken leg was too early however fully treated and his thighbone did not begin to recovery yet. In these extreme incidents the whole stresses are carried by the plates. For the detachedness of this project we compared analyses combinations of the two types osteosynthesis plates models applied to two different thighbone diaphysis fractures models. The modeling and calculations was done using FEM software ANSYS Workbench. This project was done within the framework of the institutional research plan, identification code MSM6840770043.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Kostelecká, M.; Kolísko, J.; doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2012, 11th Youth Symposium on Experimental Solid Mechanics - book of abstrakt, Brasov, Transilvania University of Brasov), p. 126-127), ISBN 978-606-19-0079-4

Anotace:

The subject of the article is a set of results from series of tests carried out on nine mixture formulas. Asbestos-free plates bonded by hydro-silicate matrix and reinforced by organic fibres were produced from these mixture formulas.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

Jahoda, J.

Publikováno:

2011

Anotace:

Diplomová práce pojednává o měření pole deformací a posunutí pomoci nekontaktní optické metody DIC. Čtenář je seznámen s principem metody DIC, výpočtu deformace z pole posunutí, geometrickými vztahy soustavy, s vnitřními a vnějšími parametry záznamové kamery a z transformací kamery. Součástí diplomové práce bylo zásadní přepracování a rozvinutí programu z bakalářské práce pro výpočet DIC. Je popsána vnitřní struktura programu a všechna vylepšení, která na něm byla, jako součást práce provedena. Velkým pokrokem bylo přidání grafického rozhraní a kompilace do samostatné aplikace, což umožní snadnou obsluhu. Je popsán základ tvorby GUI v jazyce Matlab, následuje manuál pro snadnou obsluhu programu. Kapitola komerční aplikace ukazuje konkurenční komerční programy. Je provedena za účelem ověření kalibrace na sérií testů. V rámci programu bylo provedena řada experimentů, včetně přetvoření na ortotropním prvku mostu, výsledky jsou zdokumentované a popsané v kapitole experimenty. Práce je int

Typ:

Diplomová práce

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.

Publikováno:

2011, Engineering Mechanics 2011, Praha, Ústav termomechaniky AV ČR), p. 355-358), ISBN 978-80-87012-33-8

Anotace:

Changes of mechanical properties, namely of modulus of elasticity, often play a role of damage accumulation indicators in the framework of fatigue behaviour of composite materials. In order to improve the reliability of these indicators for identification of material degradation process it is necessary to eliminate the influence of external loading and volume forces associated with thermal expansion of heterogeneous material at various temperatures. Therefore the paper deals with description of experimental assessment of relation between external load and material stiffness and also studies the dependency of material stiffness on temperature. For the monitoring of degradation process ultrasonic measurement was used. Obtained results are discussed with respect to fatigue testing of material and also interpreted from the micromechanical point of view.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Ing. Tomáš Doktor, Ph.D.

Publikováno:

2011

Anotace:

The paper deals with development of a software tool for assessment of pore size distribution of porous materials. Six types of materials were tested: lime mortars, frit glass, polyurethane foam, polyvinylchloride foam and of human and porcine trabecular bone. Process of preparation of samples is described in order to achieve suitable specimen for image acquisition. For the acquisition of 2D image data four methods were used: CCD camera, scanning electron microscope, laser confocal microscope and high resolution flatbed scanner. The procedure consists of image segmentation, connected component analysis and stereological calculation. A series of mercury intrusion porosimetry measurements was performed and the results were compared with the results of image analysis. Comparison of both groups of results shows a satisfactory agreement. Suitability of developed tool is discussed regarding to type of tested material and to range of pore sizes present in the structure.

Typ:

Diplomová práce

Autoři:

Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Sekyrová, K.; Králík, V.; Němeček, J.

Publikováno:

2011, Chemické listy, 105 (17), p. 729-732), ISSN 0009-2770

Anotace:

The presented paper outlines experimental investigation that is a part of an extensive research plan of study of fatigue properties of aerospace industry grade CRFP laminates. These materials are relatively novel and their long-term behavior and degradation are not yet completely described. Deterioration of this complex material in cyclic loading conditions is to be evaluated by several criteria based on evolution of certain of mechanical properties. Among the criteria is a decrease of modulus of elasticity. In order to reliably detect the changes in this property sensitive three point bending experimental setup was prepared, calibrated and compared to the results of the independent ultrasound method yielding the dynamical modulus of elasticity. Simultaneously, the local mechanical properties were studied by nanoindentation in order to set a reference point for a successive measurement after fatigue tests.

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Ing. Petr Koudelka, Ph.D.; Jiroušek, O.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 64-65), ISBN 978-1-63439-434-5

Anotace:

This paper is aimed at the study of mechanical behavior of aluminium metal foams by modeling their internal structure and analysis using finite element method. Alporas aluminium foam was selected as a reference material and the material characteristics are derived from tensile loading using numerical FEM analysis in ANSYS software. Internal structure is modeled by 2 different methods - using voxel model created on the basis of a series of CT scans and by discretization using Gibson-Ashby's cellular model. Mechanical behavior analysis is performed in both elastic and plastic fields. Investigated mechanical characteristics are particularly the evolution of overall Young's modulus according to different relative densities and in the plastic field tensional stress-strain diagram. The beam-only discretization is considered intentionally to investigate its suitability for modeling of closed cell foams. Finally, FEM numerical results are compared to Gibson-Ashby's mathematical model.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.

Publikováno:

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 127-128), ISBN 978-1-63439-434-5

Anotace:

Knowledge of trabecular bone behaviour under loading is very important for the bone quality assessment. For investigation of deformation behaviour of trabecular bone a combination of computational and experimental method was used. In this study suitable visco-elasto/plastic material model for single trabeculae was established from numerical simulation of nanoindentation test. The visco-elasto/plastic model with von Mises yield criterion and bilinear isotropic hardening with implicit creep was chosen. Pure elastic material constants can be determined directly from nanoindentation test by Oliver-Pharr method. Other constants determining the plastic and creep behaviour of the model have to be identified indirectly by fitting the load-displacement curve to results from the Finite Element (FE) simulation of nanoindentation test. For statistically significant fitting procedure a multiple indents (10um grid size) with different loading rates, holding times and peak loads were performed.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, J.; doc. Ing. Petr Zlámal, Ph.D.; Kostelecká, M.

Publikováno:

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 71-72), ISBN 978-1-63439-434-5

Anotace:

Article deals with describing of the pre-testing procedure for the uniaxial testing, nanoindentation and finite element modeling of single trabeculae. The first part is focused on the specimen resection, delipidation and fixation in a novel high precision experimental device which enables to measure the strains optically using a high-resolution CCD camera. The second part deals with the development of the volumetric model of the trabecula required for numerical analysis. The last part is dedicated to optimization of polishing procedure used sample surface preparation for nanoindentation. Effect of the grain size, load and duration time of the grinding on final surface roughness was analyzed. Change in the surface roughness was monitored during the preparation process using a confocal microscope. Optimized procedure of sample preparation for micro-mechanical testing with satisfactory results is presented in the paper.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.

Publikováno:

2011

Anotace:

The aim of the research was to investigate the cemented bone-implant interface behavior with emphasis on the imaging techniques suitable to detect early defects in the cement layer. To simulate in vivo conditions a polyethylene acetabular cup was implanted into the human pelvic bone using commercial polymethacrylate bone cement. The implanted cup was then loaded in a custom hip simulator to initiate fatigue crack propagation in the bone cement. The pelvic bone was then scanned repetitively in a micro-tomography device. The reconstructed tomography images showed failure processes that occurred in the cement layer during the first 250,000 cycles. A failure in cemented acetabular implant-debonding, crumbling and smeared cracks -- was found at the bone--cement interface. The use of micro-focus source and large high resolution flat panel detector allowed to reconstruct the micro-structural models suitable for investigation of migration, micromotions and consecutive loosening of the implant.

Typ:

Disertační práce (PhD)

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.; doc. Ing. Petr Zlámal, Ph.D.; Pokorný, D.

Publikováno:

2011, Frattura ed Integrita Strutturale, 5 (15), p. 5-13), ISSN 1971-8993

Anotace:

The quality of bonding between the acetabular cup and pelvis bone plays a key role in total hip replacement stability. One of the source of potential loss of the primary stability is the cement layer degradation. The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of the sample of pelvic bone with implanted cemented acetabular component. The process of damage accumulation in cement fixation was monitored by repeated scanning using high resolution micro Computed Tomography. Use of microfocus source and large high resolution flat panel detector allows investigation of structural changes as well as development of full-scale micro-structural models.

DOI:

10.3221/IGF-ESIS.15.01

Typ:

Článek v odborném recenzovaném periodiku

Autoři:

Micka, M.

Publikováno:

2011, Bezpečnost a integrita vysokotlakých plynovodů, Praha, Český plynárenský svaz), p. 179-200), ISBN 978-80-904619-2-5

Anotace:

Kapitola se zabývá vlivem posuvu půdy na napjatost v plynovodním potrubí. Nejprve jsou popsány metody sledování a měření posuvů půdy v ohrožených oblastech geotechnickým a geodetickým měřením.. Dále jsou popsány výpočtové metody k určení dodatečného namáhání potrubního systému vyvolaném posuvy zeminy. Je uveden postup výpočtu modifikovanou deformační metodou a řešení užitím metody konečných prvků. V závěru kapitoly je uveden příklad určení přídavného napětí v potrubí v konkrétní sledované lokalitě.

Typ:

Kapitola v jiné knize česky

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.; Kostelecká, M.

Publikováno:

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 45-46), ISBN 978-1-63439-434-5

Anotace:

This article is focused on assessment of pore size distribution of a porous material. Improvements of the analysis procedure and of the software tools are presented. For the comparison of reliability of the presented method specimena of various origins were tested. As representatives of biological materials specimena of human and porcine trabecular bone were tested, as representatives of artificial materials synthetic pumice and frit glass were used. Images required for the image analysis were captured using a CCD camera, a high resolution flatbed scanner and a confocal microscope. The different methods used to acquire the images are discussed regarding to the range of the pore size, dimensions of the available specimen and properties of the specimen surface. Used image processing algorithms were tested and improved regarding to the variable shape of the voids present in the material structure.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Tomáš Fíla, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Šperl, M.

Publikováno:

2011, Experimentální analýza napětí 2011, Brno, Brno University of Technology), p. 49-55), ISBN 978-80-214-4275-7

Anotace:

The article deals with assessment of fatigue degradation of C/PPS composites using simple acoustic measurement technique. Changes in natural frequency and attenuation decrement were chosen as indicators of fatigue damage accumulation in the studied composite material. New testing device was developed for acoustic measurement. The experimental setup was designed to chime the specimen by repeatable force of stiff striker exciting a specific natural mode of vibration and to record the acoustic response of the specimen to the impact simultaneously. From the power spectral density of the signal the natural frequency was obtained. Using the same signal, the attenuation decrement was estimated from regression of the its envelope. Presented high precision non-destructive method allows to conclusively measure the natural frequency and its change with a deviation smaller than a few tenths per cents.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Machek, V.

Publikováno:

2011, Progresivní a netradiční technologie povrchových úprav, Jaroměř, Kudláček Jan, Ing.), p. 40-42), ISBN 978-80-904502-9-5

Anotace:

Systémy označení ocelí na odlitky podle ČSN 42002 a litin podle ČSN 42002 a ČSN EN 1560

Typ:

Vyzvaná předn. uvedená ve sborníku z lokální konf. česky

Autoři:

Machek, V.

Publikováno:

2011, Progresivní a netradiční technologie povrchových úprav, Jaroměř, Kudláček Jan, Ing.), p. 29-39), ISBN 978-80-904502-9-5

Anotace:

Systém značení ocelí podle norem ČSN 42002 a ČSN 10027-1 a ČSN 10027-2

Typ:

Vyzvaná předn. uvedená ve sborníku z lokální konf. česky

Autoři:

Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.

Publikováno:

2011, Engineering Mechanics 2011, Praha, Ústav termomechaniky AV ČR), p. 115-118), ISBN 978-80-87012-33-8

Anotace:

This paper deals with pore size distribution assessment of trabecular structure of human proximal femur. Two distinct methods for estimation of the pore size distribution histograms are tested, mercury intrusion porosimetry and image analysis. For the image analysis two-dimensional images of crosssections of the specimens were used and the pore size distribution was estimated using a stereological calculation method based on the geometrical properties of an idealized pore. Comparison of the results of both methods is presented. Suitability of both methods for biological materials is discussed regarding to mechanical properties of these materials, characteristics of pores and range of pore sizes present in the structure.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Jiroušek, O.; doc. Ing. Daniel Kytýř, Ph.D.; Kunecký, J.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Němeček, J.

Publikováno:

2011, Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computiing, Edinburgh, Civil-Comp Press), p. 1-12), ISBN 978-1-905088-46-1, ISSN 1759-3433

Anotace:

The paper presents a comparison between mechanical properties of single human trabeculae obtained by micromechanical testing and those assessed by nanoindentation. Compact uniaxial tension/compression device has been developed for this purpose. The strains at the surface of the sample are measured optically using a high-resolution CCD camera. The strain field is evaluated using image correlation technique. Local micromechanical properties were assessed using nanoindentation. From obtained nanoindentation curves material parameters for elasto-plastic constitutive model with isotropic hardening are identified in a FE simulation of the indentation process. The unknown parameters are identified in a large set of parametric studies in which the response of the model is best-fitted to the experimental curve. Validation of the material model obtained from nanoindentation is presented in simulation of the tensile test of single trabecula.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Jiroušek, O.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Kroupa, M.

Publikováno:

2011, Nuclear Instruments and Methods in Physics Research, Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, 633 (Supp. 1), p. S148-S151), ISSN 0168-9002

Anotace:

A micro-radiographic system composed of microfocus X-ray tube and a large flat panel detector has been adapted for imaging complicated internal microstructure of trabecular bone under applied deformation. To capture the deforming microstructure a load was applied in small increments while the sample was tomographically scanned. Reconstruction of the internal structure is provided using backprojection algorithm for equiangular cone-beam projection data. From the reconstructed cross-sections a finite element (FE) model of the microstructure was developed and loaded according to the experiment. Deformation behavior of the FE model was compared to the experimentally determined response of the sample.

DOI:

10.1016/j.nima.2010.06.151

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

Žďárský, M.

Publikováno:

2011

Anotace:

Cílem diplomové práce, je vypracovat metodický rámec analýzy plastické deformace v tahově zatěžovaných materiálech. Tato analýza bude vycházet ze zatěžovacích dat a záznamu vývoje teplotního pole na povrchu vzorku. Invertováním úlohy o přechodovém šíření tepla dopočítat na základě popsaného šíření tepla polohu a intenzitu zdrojù tepla, kterými jsou místa plastického přetvoření. Znalost vývoje plastické deformace v prùběhu experimentu využít pro hledání funkce zpevnění daného materiálu, která bude mezi kandidátskými funkcemi a parametry určována na základě minimální odlišnosti mezi výsledkem měření a předpovědí výpočtu. Aplikovat metodu na rozlišení tvárného chování plynovodních ocelí v rùzných stavech - ocel ve stavu po výrobě a po vyžíhání.

Typ:

Diplomová práce

Autoři:

Kostelecká, M.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 61-62), ISBN 978-1-63439-434-5

Anotace:

Results from series of tests carried out on nine mixture formulas are the main data set. Asbestos-free plates bonded by hydro-silicate matrix and reinforced by organic fibers were produced from these mixture formulas. Within the scope of this project, the following activities were carried out: finding out the dimensional and weight characteristics of the plates, bending strength under normal conditions, the influence of frost on bending strength, the influence of putting the plates into hot water on bending strength, the impermeability of plates and measurement of change of length in the direction along and across the fibers.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Jahoda, J.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2011, 19th Annual Conference Proceedings Technical Computing Prague 2011, Praha, Vydavatelství VŠCHT Praha), p. 53-56), ISBN 978-80-7080-794-1

Anotace:

This article presents the implementation of a non-invasive optical method - Digital Image Correlation. First it discusses the basic principle of how the DIC works, covers to innovative improvements like the process of subpixel approximation, global data smoothing and process of image sequencing. The presented DIC application is compared to other commercial applications and systems. The application is provided with the GUI, which enables easy to learn and simple usage for the novice user. The output of the application contains the 2D plots of displacement and strain fields.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Micka, M.

Publikováno:

2011, The Thirteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-46-1, ISSN 1759-3433

Anotace:

Dampening capability of the protective bicycle helmet during fall is proved experimentally by drop test. From measured values of acceleration in gravity centre of the dummy head it derives HIC criterion, which represent level of the dampening quality protection of the head against effects of overloading. Drop test can be simulated numerically by LS DYNA programme. Model of the dummy head is created in accordance with test standards, model of the helmet is made out from 3D scanning for three model variants - without hardening of the surface, with hardening outer or over all surface. Values of the HIC criteria are determinated from estimated results of accelerations during the drop test simulation.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Jiroušek, O.

Publikováno:

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 155-157), ISBN 978-88-95940-30-4

Anotace:

Article deals with pore size distribution assessment of porous materials using image analysis. Test samples used in the study were prepared from metal foams and porcine trabecular bone. Two- and threedimensional images were obtained by SEM (scanning electron microscopy) and a high resolution flatbed scanner. For the pore size distribution assessment various methods were used, depending on input data properties (method of obtainig image data) and on pores characteristics (different approach should be used for closed or opened pores). For pore size evaluation using 2D images 25F Association method [5] was used. For verification of the developed algorithms MIP (mercury intrusion porosimetry) measurements were performed, but only in case of trabecular bone samples, because opened pores are necessary for these measurements. Presented algorithms were verified using artificial data structures.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2010, Proceedings of the Seventh IASTED International Conference, Innsbruck, IASTED), p. 67-71), ISBN 978-0-88986-827-4

Anotace:

The paper deals with investigation of the trabecular bone behaviour during compression test. Paper describes loading test of trabecular bone specimen using real-time Computer Tomography scanning and its simulation by Finite Element Method. Model for the Finite Element simulation was obtained using the reconstruction from tomographic projections of the zero deformation state. Deformation states were reconstructed to assess the three-dimensional strain field in the microstructure and compared with results from FE simulations. Assessment of the material model was based on nanoindentation experiment. The nanoindentation test of the trabecular bone sample was performed and the material model was identified from FE simulation of the nanoindentation test.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Ing. Jaroslav Valach, Ph.D.; Žďárský, M.; Jahoda, J.

Publikováno:

2010, Experimental methods and numerical simulation in engineering sciences, Wuppertal, Bergische Universität Wuppertal), p. 52-53)

Anotace:

Development of the presented method is a part of the complex program devoted to the investigation of the fracture properties of ductile metals in the states far from the applicability of the linear fracture mechanics theory. The method combines experimental and numerical techniques for detailed study of behavior of ductile specimens in loading preceding failure. The experimental part of the method is based on simultaneous measurement of displacements on the specimen surface by the digital image correlation method and also on recording of the temperature field of the speci-men, as the temperature field is an important variable influencing crack behavior. The displacements and temperatures are then combined in the finite elements model used for calculation of other relevant properties for description of the deformation process. The method is intended for evaluation of fracture mechanics criteria and for study of brittle to ductile transition of materials.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.; Zlámal, P.; Pokorný, D.

Publikováno:

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 151-154), ISBN 978-88-95940-30-4

Anotace:

The quality of bonding between the acetabular cup and pelvis bone plays a key role in total hip replacement stability. One of the source of potential loss of the primary stability is the cement layer degradation. The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of the sample of pelvic bone with implanted cemented acetabular component. The process of damage accumulation in cement fixation was monitored by repeated scanning using high resolution micro Computed Tomography. Use of microfocus source and large high resolution flat panel detector allows investigation of structural changes as well as development of full-scale micro-structural models.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.; doc. Ing. Petr Zlámal, Ph.D.; Pokorný, D.; Dammer, J.

Publikováno:

2010, Proceedings of 9th International Symposium on Computer methods in Biomechanics and Biomedical Engineering, Valencia, Universidad Politécnica de Valencia), p. 467-471), ISBN 978-0-9562121-3-9

Anotace:

The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of a sample of pelvic bone with implanted cemented acetabular component. The most unfavorable activity (downstairs walking) was simulated in two million cycles with 4Hz frequency. The process of damage accumulation in cement fixation was monitored by repeated scanning using high resolution micro-focus X-ray Computed Tomography. Use of micro-focus source and large high resolution flat panel detector allows investigation of structural changes as well as development of full-scale micro-structural models. 3D high resolution finite element model was reconstructed from the microCT data. The FE model is suitable for prediction of bone-implant interface behaviour.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Žďárský, M.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 29-31), ISBN 978-88-95940-30-4

Anotace:

The aim of research is to develop a reliable method for studying of evolution of plastic deformation during the loading process by comparing temperature field measured by thermo-camera with FEA model on CT specimens. The presented method is noninvasive and non-contact. For strain measurement is used thermoplastic phenomenon, which is a typical for local raise of the temperature in deformed places. The loads and the boundary conditions used in the experiments are input to the mechanical FEA model and after analysis we can compare the computed density of the plastic work with the density of heat energy known from experiment. The FEA model and the experiment yield similar results. The description and modeling of regions far away from the notch involves consideration of more complex physics (transition phenomena) therefore the differences of maximum values of heat between experiment and simplified model are bigger.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Jahoda, J.; Ing. Jaroslav Valach, Ph.D.

Publikováno:

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 158-160), ISBN 978-88-95940-30-4

Anotace:

This contribution presents application of digital correlation method for optical measurement of displacements and techniques for improvement of data processing. The main point of the paper is a comparison of two different techniques of the data processing of the same experiment. First one is based on determination of the displacement field using the image of studied body surface at the beginning and at the end of load application, while the second evaluation technique relies on sequential evaluation and addition of the partial displacement fields derived from comparison of adjacent image pairs in the sequence. It is shown that the later approach is favorable from the point of view of the total error of the experimental results. This observation is especially true in the case of large deformations as explained in the final discussion of the paper.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

prof. Ing. Josef Jíra, CSc.; Micka, M.; Puchmajer, P.

Publikováno:

2010, ISBN 978-80-01-04592-3

Anotace:

Skriptum je určeno posluchačům bakalářského studia Fakulty dopravní ČVUT. V sedmi kapitolách jsou uvedeny řešené příklady ze základů kinematiky a dynamiky, dyańamiky tětes a soustav, kmitání soustavy s jedním astupněm volnosti a teorie středového rázu těles.

Typ:

Vysokoškolské skriptum v češtině

Autoři:

prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Micka, M.

Publikováno:

2010, ANSYS 2010, Praha, TechSoft Engineering), p. 1-8), ISBN 978-80-254-8388-6

Anotace:

Tlumící schopnost ochranné cyklistické přilby při pádu se zkouší experimentálně pádovou zkouškou. Z naměřených hodnot zrychlení v těžišti makety hlavy se odvozuje HIC kritérium, kterým se vyjadřuje úroveň tlumících vlastností ochrany hlavy před účinky přetížení. Pádovou zkoušku lze simulovat numericky v programu LS DYNA. Model makety hlavy je vytvořen podle zkušební normy, model helmy z 3D skenování pro tři varianty - bez zpevnění povrchu, se zpevněním vnějšího či celého povrchu. Z výsledků zjištěných zrychlení při modelování pádového testu jsou určeny hodnoty kritéria HIC.

Typ:

Stať ve sborníku z lokální konf. česky

Autoři:

Jiroušek, O.; prof. Ing. Josef Jíra, CSc.; Hrdlička, O.; Kunecký, J.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Vyčichl, Ph.D.; Ing. Tomáš Doktor, Ph.D.

Publikováno:

2010, Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 224 (4), p. 259-267), ISSN 0954-4097

Anotace:

This article deals with finite-element (FE) modelling of the reinforcing effect of the geosynthetic material used in the construction of a ballasted track. Various different designs of geosynthetic material are studied and their reinforcing effects are evaluated in terms of the total settlement reduction. Three-dimensional FE models of the reinforced railway superstructure are compared to a reference FE model with no reinforcement. Each geosynthetic material is modelled respecting its material properties, and the interaction with the ballast material is simulated according to its primary function.

DOI:

10.1243/09544097JRRT319

Typ:

Článek v periodiku excerpovaném SCI Expanded

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.; Dammer, J.

Publikováno:

2010, Experimental methods and numerical simulation in engineering sciences, Wuppertal, Bergische Universität Wuppertal), p. 64-65)

Anotace:

Aseptic loosening is one of the most frequent reasons of failure of total hip joint replacement. The aim of the research was to investigate the processes playing role during cement degradation. To determine the degradation caused by cyclic mechanical loading radiological investigation have been used. The main problem of loosening - cement layer degradation and bone-cement interface debonding - have been investigated using a custom hip simulator. Image data from high resolution micro-focus X-ray Computed Tomography were used to reconstruct the complex geometry of the inner structure of the trabecular bone and the interface between the pelvic bone and the implant. Visualisation of trabecular bone structure and cement layer changes provided information about implant instability progress.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Jiroušek, O.; Jandejsek, I.; doc. Ing. Daniel Kytýř, Ph.D.; Dammer, J.

Publikováno:

2010, Experimental methods and numerical simulation in engineering sciences, Wuppertal, Bergische Universität Wuppertal), p. 66-69)

Anotace:

Digital Volume Correlation method is used to establish the spatial displacement and strain fields in a loaded sample of trabecular bone. The displacements are evaluated at the nodal points of underlaying FE mesh which is used to calculate the strains in each tetrahedral element. Precision of the method is evaluated using artificial image data.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

Kunecký, J.; Jiroušek, O.

Publikováno:

2010, ISBN 978-1-935116-06-6, ISSN 1046-6762

Typ:

Sborník z mezinár. konf.

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; Horníček, L.; prof. Ing. Josef Jíra, CSc.; Kunecký, J.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Vyčichl, Ph.D.

Publikováno:

2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-31-7, ISSN 1759-3433

Anotace:

This paper deals with numerical and experimental investigation of ballasted track under cyclic loading. The experimental part deals with measurement of settlements of different track bed designs under repetitive load. The designs are tested in laboratory conditions in a small-scale box filled with ballast material reinforced with different type of geosynthetics. Different thickness of the ballast and subballast layers are tested and results in terms of measured settlements at different locations are compared with FE models.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; Horníček, L.; prof. Ing. Josef Jíra, CSc.; Kunecký, J.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Vyčichl, Ph.D.

Publikováno:

2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 69-69), ISBN 978-1-905088-30-0, ISSN 1759-3433

Anotace:

Paper deals with numerical and experimental investigation of ballasted track under cyclic loading. The experimental part deals with measurement of settlements of different track bed designs under repetitive load. The designs are tested in laboratory conditions in a small-scale box filled with ballast material reinforced with different type of geosynthetics. Different thickness of the ballast and subballast layers are tested and results in terms of measured settlements at different locations are compared with FE models.

Typ:

Abstrakt ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.

Publikováno:

2009, Engineering Mechanics 2009 - Book of Extended Abstracts, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 314-315), ISBN 978-80-86246-35-2

Anotace:

Paper deals with investigation of trabecular bone microstructure using real-time microtomography. Recorded micro-CT scans are used to record spatial mechanical behaviour of bone under loading and provides detailed information about inner architecture and hierarchical structure of bone tissue.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.; doc. Ing. Petr Zlámal, Ph.D.

Publikováno:

2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 165-175), ISBN 978-1-905088-30-0, ISSN 1759-3433

Anotace:

This paper deals with utilization of finite element models of microstructure of complex materials with material properties obtained from nanoindentation to assess the overall material properties.Material properties at the trabecular level are obtained from nanoindentation. Parameters for the material models are obtained by fitting the experimental force-displacement curve with response obtained from the finite element simulation of the nanoindentation solved as an axisymmetric problem.The material model is used in further finite element analysis taking the microstructure into account

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.; Frankeová, D.

Publikováno:

2009, 8th Youth Symposium on Experimental Solid Mechanics, Budapešť, Scientific Society of Mechanical Engineers), ISBN 978-963-9058-26-2

Anotace:

Article deals with investigation of physical and mechanical properties of trabecular bone. Non-destructive ultrasonic tests and heat measurements were used to determine the modulus of elasticity of each sample. The velocity of longitudinal ultrasonic waves' propagation depends on the mechanical properties of the material, so the Young's modulus can be obtained from the formula coupling elasticity modulus, wave velocity and bone density.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Vavřík, D.

Publikováno:

2009, Engineering Mechanics 2009 - Book of Extended Abstracts, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 166-167), ISBN 978-80-86246-35-2

Anotace:

The paper deals with microstructure investigation of trabecular bone in acetabular region. Trabecular bone microstructure is the main factor of the bone quality and mechanical propertites at macroscopic level. Data from high resolution micro Computed Tomography can be used to reconstruct the complex geometry of the trabecular bone inner structure and interface between bone and implant. The data are usable as for micro-FE modeling as well as for experimental loading tests evaluation.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Micka, M.

Publikováno:

2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 1-11), ISBN 978-1-905088-31-7, ISSN 1759-3433

Anotace:

The aim of this work is to verity the usability of numerical modelling for soil construction of a railway reinforced with geosynthetics when using the ANSYS programme. For the computation model of a simple ground body the process of model creation, choice of finite elements, definition of material features, application of contact elements, definition of boundary conditions and setting the parameters of computation were verified. The bearing capacity of soil construction has great importance for practice. The reinforcement of a geogrid has a favourable effect on bearing capacity of the embankment. At the lower embankment the bearing capacity has increased by 46%, at the higher by 13%. Also the prestress of the reinforcement is favourable.

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Žák, O.

Publikováno:

2009, Engineering Mechanics 2009 - Book of Extended Abstracts, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 116-117), ISBN 978-80-86246-35-2

Anotace:

Paper deals with investigation of trabecular bone microstructure using real-time microtomography. Recorded micro-CT scans are used to record spatial mechanical behaviour of bone under loading and provides detailed information about inner architecture and hierarchical structure of bone tissue.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Kunecký, J.; Jiroušek, O.; Micka, M.

Publikováno:

2009, Proceedings of The Third International Conference on Mechanics of Biomaterials and Tissues, Kidlington Oxford OX GB, Elsevier), p. 1-11)

Anotace:

The FE model of the human head enables to describe possible injury mechanisms and to quantify design parameters of a protective helmet related to a specific impact event. It can be used also in the forensic medicine and for the analysis of consequences of traffic accidents

Typ:

Stať ve sborníku z mezinár. konf.

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Kroupa, M.

Publikováno:

2009, Book of Abstracts 11th International Workshop on Radiation Imaging Detectors, Praha, Institute of Experimental and Applied Physics,ČVUT), p. 49-49), ISBN 978-80-01-04378-3

Anotace:

To explore the possibilities of modern X-ray detectors an experimental setup with trabecular bone sample under uni-axial load in special loading device enabling time-lapse tomography was used. The load was applied gradually and after complete tomographic scanning the deformed shape was reconstructed. Collected 3-D images help to study the deformation process of the micro-structure where collapsing of individual trabeculae can be observed and compared to finite element simulations.

Typ:

Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:

Řezníček, J.; Ing. Jitka Řezníčková, CSc.

Publikováno:

2009, ISBN 80-86229-65-3

Anotace:

Příručka pro technickou praxi. Základní pojmy a vztahy z mechaniky tuhých těles, pružnosti a pevnosti a mechaniky tekutin a termodynamiky.

Typ:

Jiná kniha česky

Autoři:

doc. Ing. Daniel Kytýř, Ph.D.; Micka, M.

Publikováno:

2008, Proceedings of Workshop 2008, Praha, Czech Technical University in Prague), p. 428-429), ISBN 978-80-01-04016-4

Anotace:

The most common problem that may happen soon after hip hemiarthroplasty surgery is migration of the head of the acetabulumreplacement. In the operation records of the Orthopaedic Clinic of the 3rd Faculty of Medicine of the Charles University in Prague, the implants that migrated in different ways in the course of several months were retrieved and evaluated. There are two dominant directions of the replacement head migration: median migration into pelvis minor or migration in acetabular labrum direction. The aim of this research work is to analyse the migration of the replacement head in pelvic bone under various types of loading and shapes of acetabulum.

Typ:

Stať ve sborníku Workshop ČVUT

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.; Vavřík, D.; Jakůbek, J.; Dammer, J.; Němeček, J.

Publikováno:

2008, New trends in experimental methods together with advanced numerical modelling, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 1-2), ISBN 978-80-86246-34-5

Anotace:

Article presents a combination of experimental and computational approach to determine apparent modulus of elasticity of trabecular bone. Voxel FE models with voxel size of 15 µm3 are used to calculate the overall material properties.

Typ:

Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:

prof. Ing. Ondřej Jiroušek, Ph.D.

Publikováno:

2008, Proc. of 79th Annual Meeting of the International Association of Applied Mathematics and Mechanics, Bremen, International Association of Applied Mattematies and Mechanics), p. 43-43)

Anotace:

One of the possibilities to study the failure behavior of trabecular bone is to use a high-resolution FEM models of trabecular structure created based on microfocus X-ray computed tomography. Material properties of the bone tissue can be obtained using e.g. nanoindentation which provides Young's modulus of elasticity with high confidence. The key part in the computational analysis of the structure is the plasticity criteria to be chosen for the tissue. In this work a thorough comparison of different plasticity criteria, both using isotropic and orthotropic hardening is presented and results in terms of overall response is given.

Typ:

Stať ve sborníku z mezinár. konf.

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Katedry/ústavKatedra mechaniky a materiálů (K618)

Publikace katedry

Ageing Effects on the Mechanical Properties Stability of 3D Printed Material Under Compression

Discovering chiral auxetic structures with near-zero Poisson's ratio using an active learning strategy

Dynamic Bending Test with in-Situ X-Ray Radiography for Investigation of Ultra High Performance Concrete Reinforced by Steel Fibers

Dynamic characterisation of novel three-dimensional axisymmetric chiral auxetic structure

Flash X-ray radiography of internal damage in soft cellular materials during instrumented dynamic penetration

On the automatic construction of interface coupling operators for non-matching meshes by optimization methods

Split Hopkinson bar and flash X-ray characterization of ultra high performance concrete reinforced by steel fibers subjected to dynamic compression

Asynchronous time integration while achieving zero interface energy

Asynchronously in time integrated interface dynamics problem while maintaining zero interface energy

Design exploration of additively manufactured chiral auxetic structure using explainable machine learning

Effect of aging on mechanical properties of 3D printed samples using stereolitography

Effect of the long-term storage methods on the stability of cartilage biomechanical parameters

Energy-conserving interface dynamics with asynchronous direct time integration employing arbitrary time steps

Experimental evaluation of aluminothermic welds

Explicit asynchronous time scheme with local push-forward stepping for discontinuous elastic wave propagation: One-dimensional heterogeneous cases and Hopkinson bar experiment

HIGH-SPEED X-RAY RADIOGRAPHY FOR EXPERIMENTS IN IMPACT DYNAMICS USING HIGH-POWER X-RAY TUBE, CESIUM IODINE SCINTILLATOR AND LABORATORY OPTICAL CAMERA

Instrumented dynamic penetration of sandwich panels with auxetic and non-auxetic core using direct impact Hopkinson bar

MECHANICAL PROPERTIES OF BASALT: A STUDY ON COMPRESSIVE LOADING AT DIFFERENT STRAIN RATES USING SHPB

Motostudent electric 2022/23 Design project

New Technology and Logistics on the Railway

Response of the Ultra High Performance Concrete under dynamic compressive loading

Stereolithography for manufacturinf of advanced cellular metamaterials

The localized Lagrange multipliers method for finite element analysis of 3D printed composite specimens

Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics

Analytical and Experimental Analysis of Stress Uniformity in Specimen During Direct Impact Hopkinson Bar Test

Compression behaviour of TPMS-filled stainless steel tubes

Damage Localization and Failure of Stainless Steel Specimens Manufactured using Powder Bed Fusion Investigated at High Strain Rates

Effect of Polymeric Fillers on Poisson’s Function in Additively Manufactured Auxetics

Elastic wave propagation: Finite element discretization with Localized Lagrange multipliers domain decomposition and asynchronous integration in time

Explicit asynchronous time integrator with local time stepping method for sharp elastic wave propagation - strong heterogeneous cases and irregular meshes

Explicit asynchronous time integrator with local time stepping method for sharp elastic wave propagation - strong heterogeneous cases and irregular meshes

High Strain-Rate Compression Experiments on Ni/Polyurethane Hybrid Metal Foams Using the Split-Hopkinson Pressure Bar Technique

Low-Velocity Penetration Resistance of Sandwich Panels with Auxetic and Non-Auxetic Core using Direct Impact Hopkinson Bar

MotoEngineering Italy - CTU Lions Tech Details

Numerical model of open Hopkinson pressure bar and its utilisation for inverse numerical analysis of closed-cell aluminium foam

Numerical modeling of auxetic lattices subjected to dynamic compression in SHPB

Open Hopkinson Bar as a Method for Impact Testing of Additively Manufactured Cellular Metamaterials

Strain Rate-Dependent Compressive Properties of Bulk Cylindrical 3D-Printed Samples from 316L Stainless Steel

Strain-rate dependent compressive properties of inverted honeycomb lattice and bulk cylindrical samples 3D printed by MSLA method

Comparative analysis of freight transport prognoses results provided by transport system model and neural network

Compressive behaviour of additively manufactured periodical re-entrant tetrakaidecahedral lattices at low and high strain-rates

Dynamic deformation behaviour of chiral auxetic lattices at low and high strain-rates

Dynamic impact testing of cellular solids and lattice structures: Application of two-sided direct impact Hopkinson bar

Dynamic penetration of cellular solids: Experimental investigation using Hopkinson bar and computed tomography

Hybrid Auxetic Structures: Structural Optimization and Mechanical Characterization

Impact Behavior of Additively Manufactured Stainless Steel Auxetic Structures at Elevated and Reduced Temperatures

Modelling and simulation of controlled depth abrasive water jet machining (AWJM) for roughing passes of free-form surfaces

Phase-contrast and dark-field imaging for the inspection of resin-rich areas and fiber orientation in non-crimp vacuum infusion carbon-fiber-reinforced polymers

Mechanical Behavior of Materials under High Strain-rates Investigated by SHPB

Motostudent Electric 2019/20 design project

Motostudent Electric 2019/20 innovation research report

Numerical modelling of auxetic structures

Katedry/ústav
Katedra mechaniky a materiálů (K618)