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Department of Mechanics and Materials (K618)

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Department Publications

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Authors:
Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Jaromír Kylar; Kotek, V.; Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.
Published:
2025, Measurement: Sensors, p. 1-7), ISSN 2665-9174
Annotation:
In this contribution, we introduce a control system and instrumentation of the in-house developed dynamic testing device with linear motors suitable for experiments ranging from quasi-static regime up to intermediate strain rates with impact velocities of up to 8 m/s. In the contribution, we demonstrate the temporal resolution of the whole system to perform dynamic experiments with closed-loop control of displacement, velocity, or force within a period of a few milliseconds. Frequency bandwidth and testing capabilities of standard membrane pancake load-cells as well as quartz-based piezoelectric load-cells for impact testing are analysed. The system is combined with high-resolution optical inspection, high-speed photography, or even X-ray imaging. The advantages of the device and instrumentation are demonstrated in a case study revealing its potential.
DOI:
10.1016/j.measen.2024.101674
Type:
Článek v odborném recenzovaném periodiku

Authors:
doc. Ing. Petr Zlámal, Ph.D.; Ing. et Ing. Radim Dvořák; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; Ing. Ján Kopačka, Ph.D.; Ing. Jaromír Kylar; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
2025, Measurement: Sensors, ISSN 2665-9174
Annotation:
Hopkinson pressure bar is a commonly used technique to test the response of a specimen to shock load under constant strain rate to determine its material parameters. In addition to that, we propose that the Hopkinson bar apparatus can be employed to test the response of the specimen in the sense of frequency analysis; that is, specimens made of a complex metamaterial could behave as a filter of specific frequencies. Here, several difficulties arise. The structure of the metamaterial affects only those waves that have a wave length comparable to the specific length in the metamaterial of the specimen. However, the bar geometry of the apparatus itself behaves as a low-pass filter, so the high frequencies are attenuated with distance traveled. Hence, here we have the situation that the longer the specimen is, we lose the ability to investigate high frequencies, and, at the same time, the shorter the specimen is, the higher the lowest affected frequency is. Our contribution is to find a compromise for the length of the sample and to design a high-frequency testing method for such an investigation of metamaterials.
DOI:
10.1016/j.measen.2024.101673
Type:
Článek v odborném recenzovaném periodiku

Authors:
Ing. Veronika Drechslerová; Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.
Published:
2024, Vol. 48 (2024): 19th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 15-21), ISBN 978-80-01-07358-2
Annotation:
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
Type:
Stať ve sborníku z prestižní konf. (Scopus)

Authors:
Bc. Blanka Žaloudková; Koudelka, P.; Frýdlová, P.; Drozdenko, M.; Šleichrt, J.; doc. Ing. Daniel Kytýř, Ph.D.
Published:
2024, Acta Polytechnica CTU Proceedings, Praha, České vysoké učení technické v Praze)
Annotation:
The aim of this work is to develop an experimental method suitable for the mechanical testing of highly non-standard biological samples such as snake skin with osteoderms. The objective of the method is to determine, whether the osteoderms provide a protective function for the animal in its natural environment. For this purpose, a simulation of rodents biting the skin based on uni-axial compressive loading using a synthetic tooth as a penetrator was developed with an emphasis on integration with X-ray scanners to facilitate in-situ testing. To identify and characterise the structure of snake skin and to prove the protective function of osteoderms, all samples were subjected to high resolution X-ray computed tomography. The results of the experiments are presented in the form of stress-strain curves and a map of the tangent modulus.
DOI:
10.14311/APP.2024.48.0061
Type:
Stať ve sborníku z prestižní konf. (Scopus)

Authors:
Dr. Afdhal Afdhal; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Dwianto, Y.B.; Palar, P.-S.
Published:
2024, Materials & Design, 244, p. 1-13), ISSN 1873-4197
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Hurtig, K.
Published:
2024, Transforming Construction: Advances in Fiber Reinforced Concrete, Springer Nature), p. 573-580), ISBN 978-3-031-70144-3, ISSN 2211-0844
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Mauko, A.; Emre Yilmaz, Y.; Novak, N.; Ing. Tomáš Doktor, Ph.D.; Vesenjak, M.; Ren, Z.
Published:
2024, Composite Structures, 333, p. 1-10), ISSN 0263-8223
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Duarte, I.
Published:
2024, Materials Letters, 2024 (354), p. 1-4), ISSN 0167-577X
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. et Ing. Radim Dvořák; González, J.A.
Published:
2024, Computer Methods in Applied Mechanics and Engineering, 432 (Part A), ISSN 1879-2138
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2024, Emergent Materials, 2024, ISSN 2522-5731
Annotation:
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
Type:
Článek v periodiku excerpovaném databází Scopus

Authors:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Pagliaro, A.; doc. Ing. Petr Zlámal, Ph.D.
Published:
2024, ISBN 978-80-01-07358-2, ISSN 2336-5382
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Jan Falta; Ing. Michaela Jurko
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; González, J.A.; Park, K.C.
Published:
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)
Type:
Stať ve sborníku z prestižní konf. (Scopus)

Authors:
Dr. Afdhal Afdhal; prof. Ing. Ondřej Jiroušek, Ph.D.; Palar, P.S.; Ing. Jan Falta; Dwianto, Y.B.
Published:
2023, Materials & Design, 232, p. 1-13), ISSN 1873-4197
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Veronika Drechslerová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Ing. et Ing. Radim Dvořák; doc. Ing. Daniel Kytýř, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Bc. Blanka Žaloudková; Sekorová, Š.; Kopecká, B.; doc. Ing. Daniel Kytýř, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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
Published:
2023, Computer Methods in Applied Mechanics and Engineering, 413, p. 1-26), ISSN 1879-2138
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Lukáš Zeman; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Nela Krčmářová; Koudelková, V.; Zeman, J.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf. (Scopus)

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.
Published:
2023, Wave Motion, 121, ISSN 0165-2125
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf. (Scopus)

Authors:
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.
Published:
2023, Advanced Engineering Materials, 25 (24), ISSN 1527-2648
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Jan Falta; Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; Vavro, M.; Vavro, L.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf. (Scopus)

Authors:
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; Kotvald, T.; Derner, T.; Plášek, J.; Malec, Š.
Published:
2023
Annotation:
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.
Type:
Oponovaná technická zpráva cizojazyčně

Authors:
doc. Ing. Jitka Jírová, CSc.
Published:
2023, ISBN 978-80-01-07257-8, ISSN 2336-5382
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Čítek, D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; González, J.A.
Published:
2023, Proceedings of the 1st Conference on INAM 2023, Jihlava, Vysoká škola polytechnická Jihlava)
Type:
Abstrakt ve sborníku z lokální konf. česky

Authors:
Ing. Veronika Drechslerová; Ing. Michaela Jurko; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; Ing. et Ing. Radim Dvořák
Published:
2023, Inovace v aditivních technologiích INAM 2023, Jihlava, Vysoká škola polytechnická Jihlava), p. 13-13), ISBN 978-80-88064-66-4
Annotation:
The contribution is focused on the suitability of using stereolithography (SLA) for the production of porous structures with the potential of high impact energy absorption. SLA is an additive manufacturing technology using the principle of curing liquid resins using radiation of a certain wavelength [I. Romero-Ocaña, S.I. Molina 2022]. To assess the influence of the material used on the resulting mechanical properties, sets of test samples were made from three different resins and subsequently subjected to quasi-static uniaxial tensile and compressive tests. Stress-strain diagrams were created from the measured data and basic material properties were calculated. Based on the knowledge gained, the settings of the production process parameters were optimized to ensure the required print quality, the response of 3D printed samples to loading depending on the choice of resin used, and the overall suitability of the SLA method for the production of advanced cellular structures was evaluated.
DOI:
10.14311/APP.2023.41.0001
Type:
Abstrakt ve sborníku z lokální konf. česky

Authors:
doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Published:
2023, ISBN 978-80-01-07237-0, ISSN 2336-5382
Type:
Sborník z mezinárodní konf. v češtině

Authors:
Ing. Tomáš Fíla, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z mezinár. konf. cizojazyčně

Authors:
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.
Published:
2022, Materials Science and Engineering A - Structural Materials: Properties, Microstructure and Processing, 852 (5), ISSN 0921-5093
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 107-107)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z mezinár. konf. cizojazyčně

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Gonzalez, J.A.; Park, K.C.
Published:
2022, DD27 abstract book, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.
Published:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 35-35)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.
Published:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
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.
Published:
2022, Advanced Engineering Materials, 24 (3), ISSN 1438-1656
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 104-104)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
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.
Published:
2022
Annotation:
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.
Type:
Technická zpráva cizojazyčně

Authors:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z mezinár. konf. cizojazyčně

Authors:
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.
Published:
2022, Dynamic Behaviour of Additively Manufactured Structures & Materials, Freiburg im Breisgau, Albert-Ludwigs-Universität Freiburg), p. 187-192)
Annotation:
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.
Type:
Stať ve sborníku z mezinár. konf.

Authors:
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.
Published:
2022, Dynamic Behaviour of Additively Manufactured Structures & Materials, Freiburg im Breisgau, Albert-Ludwigs-Universität Freiburg), p. 103-110)
Annotation:
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.
Type:
Stať ve sborníku z mezinár. konf.

Authors:
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.
Published:
2022, Materials, 15 (3), ISSN 1996-1944
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Jan Falta; Yunus Yilmaz, E.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z mezinár. konf. cizojazyčně

Authors:
Ing. Vít Malinovský, Ph.D.
Published:
2021, Neural Network World, 31 (4), p. 239-259), ISSN 1210-0552
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2021, Metals — Open Access Metallurgy Journal, 11 (8), ISSN 2075-4701
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2021, Metals — Open Access Metallurgy Journal, 11 (1), ISSN 2075-4701
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2021, International Journal of Impact Engineering, 148, ISSN 0734-743X
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2021, Materials Science and Engineering A - Structural Materials: Properties, Microstructure and Processing, 800, ISSN 0921-5093
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2021, Advanced Engineering Materials, 23 (5), p. 1-15), ISSN 1438-1656
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
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.
Published:
2021, Advanced Engineering Materials, 23 (1), ISSN 1438-1656
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ozcan, Y.; Tunc, L.T.; Ing. Ján Kopačka, Ph.D.; Cetin, B.; Sulitka, M.
Published:
2021, The International Journal of Advanced Manufacturing Technology, 114 (11-12), p. 3581-3596), ISSN 0268-3768
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Glinz, J.; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ayalur-Karunakaran, S.; Zabler, S.; Kastner, J.; Senck, S.
Published:
2021, Journal of Materials Science, 56 (16), p. 9712-9727), ISSN 0022-2461
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Tomáš Fíla, Ph.D.; Kolman, R.; Ren, Z.; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
2020
Annotation:
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.
Type:
Disertační práce (PhD)

Authors:
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.
Published:
2020
Annotation:
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.
Type:
Technická zpráva cizojazyčně

Authors:
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
Published:
2020
Annotation:
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.
Type:
Výzkumná zpráva cizojazyčně

Authors:
Ing. Petr Koudelka, Ph.D.; Keršner, Z.; Vesenjak, M.; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
2020
Annotation:
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.
Type:
Disertační práce (PhD)

Authors:
Ing. Tomáš Doktor, Ph.D.; Gutermann, M.; Rusnáková, S.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
2020
Annotation:
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.
Type:
Disertační práce (PhD)

Authors:
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.
Published:
2020, ISBN 978-80-01-06793-2
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
2019, ISBN 978-80-86246-45-1
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
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.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
2019, International Conference on Nonlinear Solid Mechanics - ICoNSoM2019, Palazzo Argiletum, Roma, Italy), p. 131-131)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
Ing. Jan Falta; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
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
Annotation:
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.
Type:
Stať ve sborníku z prestižní konf.

Authors:
Adorna, M.; Bronder, S.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Adorna, M.; Reis, M.; Jung, A.; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
2019, International Conference on Nonlinear Solid Mechanics - ICoNSoM2019, Palazzo Argiletum, Roma, Italy), p. 128-128)
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
Ing. Vít Malinovský, Ph.D.; Meyer-Rühle, O.; Kyster-Hansen, H.; Böhmann, A.; Heinrich, Ch.; Leonhardt, S.; Zuiver, H.
Published:
2019, 2019 Konference - 25 let Fakulty dopravní, Praha, České vysoké učení technické v Praze), ISBN 978-80-01-06545-7
Annotation:
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.
Type:
Stať ve sborníku z fakultní konference cizojazyčně

Authors:
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.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
2019, Temperature dependence of material behaviour at high strain-rate, Politecnico di Torino), ISBN 978-88-85745-27-8
Annotation:
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.
Type:
Stať ve sborníku z mezinár. konf.

Authors:
Reis, M.; Adorna, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Published:
2019, Advanced Engineering Materials, 21 (7), ISSN 1438-1656
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. et Ing. Radim Dvořák; prof. Ing. Ondřej Jiroušek, Ph.D.
Published:
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
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
Ing. et Ing. Radim Dvořák; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Adorna, M.; Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
2019, Advanced Engineering Materials, 21 (8), ISSN 1438-1656
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
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
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
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.
Published:
2019, Temperature dependence of material behaviour at high strain-rate, Politecnico di Torino), ISBN 978-88-85745-27-8
Annotation:
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.
Type:
Stať ve sborníku z mezinár. konf.

Authors:
doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Published:
2019, ISBN 978-80-01-06670-6, ISSN 2336-5382
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
Ing. Jan Šleichrt, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Pithartová, K.; Senck, S.; Fürst, D.; Schrempf, A.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
doc. Ing. Daniel Kytýř, Ph.D.
Published:
2018
Annotation:
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.
Type:
Docentská habilitační práce

Authors:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.
Published:
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
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Authors:
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.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Adorna, M.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. et Ing. Radim Dvořák; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
2018
Annotation:
The bachelor thesis aims at a summary of findings and facts regarding wave propagation through a one-dimensional continuum, particularly through long slender bars. Furthermore, the work focuses on SHPB principles, techniques of pulse shaping, and finally, on methods of numerical mechanics. The practical part emanates from the theoretical one and offers a source code for creating a parametric model of the typical SHPB configuration for the LS-DYNA environment. The reduced configuration is then, by a finite element method, subjected to a sensitivity analysis. Then, a parametric analysis of a pulse shaper is carried out to reveal the influence of geometric properties of the pulse shaper on wave shapes. The analysis is algorithmized together with the processes involved, and thus, automated processing of results and a comparison with experimental data is enabled. The conclusion of the work thus constitutes of results of the parametric analysis and the amount of influence of pulse shaper’s geometric properties on wave shapes. Finally, automation algorithms for creating models, rendering the simulations, and evaluation of outcomes are involved.
Type:
Diplomová práce

Authors:
Adorna, M.; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Ing. Tomáš Fíla, Ph.D.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Felten, M.; Fries, M.; Jung, A.
Published:
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
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
Hudák, M.
Published:
2018
Annotation:
This Bachelor thesis "Upgrade of SHPB for Advanced Measurements in Transportation"realizes sub-elements of Split-Hopkinson pressure bar (SHPB) and its modifications. These elements are first created as models in the Autodesk Inventor software environment, followed by the relevant technical documentation and finally the elements are manufactured and applied to the SHPB. The purpose of these sub-elements is to simplify the operation and to partially increase safety. The proper function of designed parts is demonstrated using performed experiments with samples of the auxetic structure.
Type:
Diplomová práce

Authors:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Major, Z.
Published:
2018, ISBN 978-80-01-06474-0, ISSN 2336-5382
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
doc. Ing. Daniel Kytýř, Ph.D.
Published:
2018
Annotation:
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.
Type:
Habilitační přednáška

Authors:
Hos, J.; Ing. Nela Krčmářová; Jíra, A.; doc. Ing. Daniel Kytýř, Ph.D.
Published:
2017
Annotation:
Hardness tests belong among the most used tests of materials. The advantages of this type of test are its minimal destructiveness and its relatively low price. This diploma thesis is focused on creation of automated procedure for hardness mapping of porous materials. Based on this knowledge program for assessment of the most suitable location for indentation was developed. Inputs to the tool are images of porous material. Final image, that is used for identification of locations for indentation, is composed of this subimages. Output of software tool is G-code for CNC procedure. The G-code is used for experimental hardness mapping. Indents are optically inspected and size of their diagonal are measured. Finaly hardness is computed by application of Vickers hardness equation.
Type:
Diplomová práce

Authors:
prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Micka, M.; Ing. Jitka Řezníčková, CSc.
Published:
2017, Acta Polytechnica CTU Proceedings, 2017 (11), p. 22-30), ISSN 2336-5382
Annotation:
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.
Type:
Článek v odborném recenzovaném periodiku cizojazyčně

Authors:
Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Published:
2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 29-32), ISBN 978-80-01-06070-4, ISSN 2336-5382
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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
Published:
2017, Acta Polytechnica, 57 (1), p. 14-21), ISSN 1210-2709
Annotation:
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
Type:
Článek v periodiku excerpovaném databází Scopus cizojaz.

Authors:
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.
Published:
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
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
Adorna, M.; Fisher, C.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Published:
2017
Annotation:
This thesis deals with evaluation of dynamic experiments performed using a modified SHPB measuring device, particularly on materials with low mechanical impedance.. Preprocessing methodology of recorded experimental data is proposed and implemented. Furthermore, set of software tools for data processing and results evaluation is created. The software tools are implemented in a modular user interface, which allows for fast and reliable semi-automatic evaluation of SHPB experiments. Functionality of the created interface is demonstrated on two experiments with different materials. For this purpose, the experiments of laser sintered auxetic structure (with negative Poisson's ratio) and nickel-coated open-cell polyurethane foam were selected and evaluated. Obtained results are consistent and correspond with an already published. As a main output of the thesis, the graphical user interface and set of software tools for evaluation of SHPB experiments were developed and implemented.
Type:
Diplomová práce

Authors:
doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Published:
2017, ISBN 978-80-01-06070-4, ISSN 2336-5382
Type:
Sborník z mezinár. konf. cizojazyčně

Authors:
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.
Published:
2017, Advanced Engineering Materials, 19 (10), ISSN 1438-1656
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
Ing. Jan Falta; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Šperl, M.
Published:
2017
Annotation:
This thesis deals with problems of instrumentation of a Split Hopkinson Pressure Bar modified for dynamic testing of materials with low mechanical impedance. Aim of the thesis is focused on design and implementation of components related to the strain wave measurement based on strain gauges (i.e. tensometric 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). Aside from design of hardware components, the thesis also deals with development of a control software with graphical user interference that allows selection of parameters of the dynamic tests and their storage for the evaluation of experiments. The applicability and reliability of the implemented solutions is assessed by SHPB experiments with samples of auxetic structures. It is shown that the experiments were reliably evaluated and that the presented set of hardware and software technical solutions improves the quality and reliability of the testing components, while increasing the overall comfort of operation of the SHPB instrumentation, too.
Type:
Diplomová práce

Authors:
Ing. Tomáš Fíla, Ph.D.
Published:
2017
Annotation:
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.
Type:
Kandidátské minimum

Authors:
prof. Ing. Josef Jíra, CSc.
Published:
2017, ISBN 978-80-01-06140-4, ISSN 2336-5382
Type:
Sborník z fakultní konference cizojazyčně

Authors:
Ing. Petr Koudelka, Ph.D.
Published:
2017
Annotation:
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.
Type:
Kandidátské minimum

Authors:
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.
Published:
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
Annotation:
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).
Type:
Abstrakt ve sborníku z mezinár. konf.

Authors:
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.
Published:
2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 72-75), ISBN 978-80-01-06070-4, ISSN 2336-5382
Annotation:
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
Type:
Stať ve sborníku z prestižní konf.

Authors:
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.
Published:
2017, Materials and Technology, 51 (3), p. 397-402), ISSN 1580-2949
Annotation:
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
Type:
Článek v periodiku excerpovaném SCI Expanded

Authors:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Tomáš Doktor, Ph.D.; Kumpová, I.; Koudelková, V.; Nepomucká, K.; Šepitka, J.; Gantar, A.
Published:
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
Annotation:
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.
Type:
Abstrakt ve sborníku z mezinár. konf.