Lidé na fakultě
Ing. Tomáš Fíla, Ph.D.

rozklikni NABÍDKU

Publikace

informace pocházejí z univerzitní databáze V3S

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Jaromír Kylar; Ing. Vojtěch Kotek; Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2025, Measurement: Sensors, p. 1-7), ISSN 2665-9174
Anotace:
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
Typ:
Článek v odborném recenzovaném periodiku

Autoři:
Ing. Veronika Drechslerová; Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2024, Vol. 48 (2024): 19th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 15-21), ISBN 978-80-01-07358-2
Anotace:
The paper deals with the examination of the ageing effects on the mechanical properties stability of 3D printed material via stereolithography under compression when subjected to various conditions, including UV radiation, X-rays, and the effects of time, from the opening of the bottle with the material to the 3D-printing process. The sets of samples under investigation were subjected to quasi-static and dynamic compression loading using an Split Hopkinson Pressure Bar. The aim of this paper is to investigate the long-term stability of the samples in terms of their mechanical properties and material behaviour and their degradation pattern. Despite the manufacturer’s information, it was found that the mechanical behaviour of the printed samples was significantly affected by the ageing process.
DOI:
10.14311/APP.2024.48.0015
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

Autoři:
Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Hurtig, K.
Publikováno:
2024, Transforming Construction: Advances in Fiber Reinforced Concrete, Springer Nature), p. 573-580), ISBN 978-3-031-70144-3, ISSN 2211-0844
Anotace:
he Ultra high-performance steel fibres reinforced concrete (UHPFRC) investigated in this paper is a fine-grained cement-based composite material with outstanding mechanical properties. Its key attributes include an ultra-high compressive strength in excess 150 MPa and a permanent post-cracking strength in excess 5 MPa. To increase its structural integrity, steel fibres 13 mm long and 0.2 mm in diameter are added to the matrix to reinforce it. In order to assess the properties of the UHPFRC under varying loading conditions, the prism-shaped specimens are subjected to three-point bending tests over a range of loading rates from quasi-static regime to dynamic impacts at intermediate strain rates. The experiments are performed using an in-house developed testing machine based on linear motors and are conducted at 4 different loading velocities with at least 5 specimens tested at each strain rate. The tests are observed using a high-speed camera. For a better understanding of the material behaviour, the testing equipment is combined with a laboratory high power X-ray imaging set-up that allows internal inspection of the samples to analyze the effect of imperfections, inhomogeneities, voids and dominant fibre orientation. X-ray imaging is performed before and after mechanical testing and also in-situ during the loading using a high-speed X-ray imaging camera. A significant dynamic increase factor is observed between the individual strain rates, while the dominant fibre orientation is identified as a crucial aspect causing the differences between the specimens. This innovative experimental approach provides invaluable insights into the material response to dynamic loading conditions and offers a comprehensive understanding that is crucial for optimizing its performance in a variety of real-world applications.
DOI:
10.1007/978-3-031-70145-0_69
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Duarte, I.
Publikováno:
2024, Materials Letters, 2024 (354), p. 1-4), ISSN 0167-577X
Anotace:
Processes of internal damage development during localized dynamic penetration represent a crucial mechanism important for relevant analysis of deformation and failure of plates and sandwich panels under high strain rate conditions. Soft cellular materials are of special importance as the internal damage defines mode of collapse and energy absorption capabilities. In this paper, a fast X-ray radiography is employed for in-situ analysis of the internal damage development in soft closed-cell aluminum foam subjected to a localized high strain rate penetration using an instrumented projectile in a direct impact Hopkinson bar apparatus. The process with a typical duration of a few milliseconds is visualized using four X-ray projections acquired using a flash X-ray system and a high-speed camera. Internal damage such as cracking, shear failure in the vicinity of the projectile, and compaction of the material is successfully identified. This unique method utilizing a laboratory based X-ray source allows for characterization of the penetration mechanism that has been usually analyzed only in post-mortem state.
DOI:
10.1016/j.matlet.2023.135372
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Čítek, D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2024, Emergent Materials, 2024, ISSN 2522-5731
Anotace:
Excellent mechanical properties of ultra high performance concrete make it suitable for use in special applications, where the material is subjected to dynamic phenomena such as impacts, explosions, or earthquakes. This paper presents a novel experimental approach that integrates a Split Hopkinson Pressure Bar with a flash X-ray system and high-speed optical imaging to investigate the dynamic behavior of steel fiber reinforced UHPC under high strain rate uni-axial compression. In-situ Flash X-ray radiography emerges as a particularly effective tool, providing clear visualization of deformation response and overcoming challenges associated with flying debris encountered in optical inspection. Moreover, computed tomography and scanning electron microscopy appear as a vital technique for analyzing micro-structure and fiber distribution and orientation. The combined approach offers a promising method to study the dynamic behavior of steel fiber reinforced ultra high performance concrete and also holds promise for analyzing more complex modes of deformation and material interactions, providing valuable insights for enhancing the design and performance of critical infrastructure subjected to dynamic loading events.
DOI:
10.1007/s42247-024-00893-w
Typ:
Článek v periodiku excerpovaném databází Scopus

Autoři:
Ing. Veronika Drechslerová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Ing. et Ing. Radim Dvořák; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 1-5), ISBN 978-80-01-07237-0, ISSN 2336-5382
Anotace:
This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on the mechanical properties of the material and printed samples. The aging of the material could be a problem for its subsequent use as the stability of the mechanical properties would not be maintained and unwanted deterioration of the material could occur. As part of the research, sets of samples were printed and subjected to different aging methods and subsequently subjected to quasi-static and dynamic uni-axial load tests. From the data obtained, the basic mechanical properties of the material were calculated and compared with each other. The aim of this paper was to investigate whether aging process causes significant changes in the mechanical properties of the materials used, which could have a consequential impact on their use in different industries.
DOI:
10.14311/APP.2023.42.0001
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Mračko, M.; Ing. Ján Kopačka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Ing. Michaela Jurko; Ing. Václav Rada
Publikováno:
2023, Computer Methods in Applied Mechanics and Engineering, 413, p. 1-26), ISSN 1879-2138
Anotace:
The derivation and implementation of an asynchronous direct time integration scheme for domain-decomposed finite element models is presented. To maximize clarity in the description of the proposed asynchronous integration, the scheme is restricted to the linear-elastic stress wave propagation case. The proposed method allows the integration of individual subdomains with independent time steps. There is no requirement for an integer time steps ratio of the interacting domains while maintaining zero interface energy. The subdomains are connected by the condition of the continuity of the acceleration field at the interface. In addition, the a posteriori technique is applied to satisfy the continuity of the displacement and velocity fields. Another important contribution of this paper lies in the description of the implementation — we offer the reader a general description of the implementation of the case of any number of subdomains with any number of constraints between them, while the basics of the algorithm are explained on a single domain pair. The functionality of the asynchronous integrator is verified by solving selected problems and comparing with analytical solutions and experimental measurements obtained using a Split Hopkinson pressure bar setup. © 2023 Elsevier B.V.
DOI:
10.1016/j.cma.2023.116110
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.
Publikováno:
2023, Wave Motion, 121, ISSN 0165-2125
Anotace:
This is a presentation of robust and accurate explicit time-stepping strategy for finite element modeling of elastic discontinuous wave propagation in strongly heterogeneous, multi-material and graded one-dimensional media. One of the major issues in FEM modeling is the existence of spurious numerical stress oscillations close to theoretical wave fronts due to temporal-spatial dispersion behavior of FE discretization. The numerical strategy presented for modeling of 1D discontinuous elastic waves is based on (a) pushforward-pullback local stepping — ensuring the elimination of dispersion due to different critical time step sizes of finite elements, (b) domain decomposition via localized Lagrange multipliers — to satisfy coupling kinematics and dynamic equations , (c) asynchronous time scheme — ensuring the correct information transfer of quantities for the case of integer ratios of time step size for all domain pairs. Dispersion behaviors, existence of spurious stress oscillations, and sensitivity of the dispersion to time step size are then suppressed. The proposed method is numerically tested with regard to the rectangular step pulse elastic propagation problem considering in-space varying Young’s modulus. To prove robustness and accuracy, a comparison with results from commercial software, an analytical solution, and experimental data from partial assembly of a split Hopkinson pressure bar (SHPB) setup is provided.
DOI:
10.1016/j.wavemoti.2023.103169
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 77-82), ISBN 978-80-01-07237-0, ISSN 2336-5382
Anotace:
X-ray radiography and computed tomography have become well-established methods for investigation of internal structure of objects and for defectoscopy. Recently, the methods have even been used for in-situ analysis of materials under mechanical loading. Although the techniques would be very suitable for analysis during dynamic events, their application is constrained by typical achievable frame rates. Therefore, fast imaging is usually limited to facilities providing sufficient flux like particle accelerators. In this paper, we test imaging performance of a laboratory-based setup with a high-power X-ray tube, a scintillation panel, and an optical camera. Fast-rotating object and typical specimens for impact testing are irradiated with different power settings and quality of captured images is evaluated and analyzed. It is found out that the system can be successfully used for imaging at several hundred frames per second allowing for inspection of slow impact dynamics experiments.
DOI:
10.14311/APP.2023.42.0077
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Michaela Jurko; Ing. Veronika Drechslerová; Ing. Petr Koudelka, Ph.D.; Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2023, Advanced Engineering Materials, 25 (24), ISSN 1527-2648
Anotace:
The paper deals with the dynamic penetration of 3D printed panels with auxetic and conventional honeycomb unit cell-based cores. The geometry of the unit cells and their periodic assembly in the resulting lattices were selected to ensure the same relative density and overall weight of the individual sample types. Such a similarity of both specimen types allowed the evaluation of differences between conventional and auxetic lattices in terms of penetration characteristics and deformation energy mitigation properties. Dynamic penetration of the samples was performed using a fully strain-gauge instrumented Open Hopkinson Pressure Bar (OHPB) at three impact velocities resulting in three loading scenarios. All performed experiments were captured by two optical cameras for detailed observation and for tracking of an impactor movement using Digital Image Correlation (DIC). The force-penetration depth relation was used to evaluate the elastic and post-yield compression characteristics of the lattices together with their deformation energy mitigation capabilities. The results show that the main differences in the deformation response of lattices consist of lower overall stiffness and effective yielding of the auxetic lattices at higher penetration depth. Numerical simulation using an explicit solver was performed to analyze the deformation mechanism of the individual core types.
DOI:
10.1002/adem.202300980
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Falta; Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; Vavro, M.; Vavro, L.
Publikováno:
2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 17-21), ISBN 978-80-01-07237-0, ISSN 2336-5382
Anotace:
This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic conditions, while standard uni-axial loading device is used for evaluation in quasi-static conditions. Basalt specimens were subjected to four different loading-rates from 200-600 s−1 on which the stress-strain dependence was evaluated together with DIC analysis of crack initiation and disintegration process. Understanding the mechanical properties of basalt can provide insights for engineers and designers in creating structures that are durable and able to withstand different loading conditions. The findings of this study can have implications for a wide range of industries, including aerospace, automotive, and construction, among others.
DOI:
10.14311/APP.2023.42.0017
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

Autoři:
Ing. Nela Krčmářová; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Čítek, D.
Publikováno:
2023, Vol. 42 (2023): 18th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze), p. 51-54), ISBN 978-80-01-07237-0, ISSN 2336-5382
Anotace:
Ultra high performance concrete is a modern cementitious material which exhibits excellent mechanical properties such as damage tolerance, fracture toughness and durability. These features make this materials suitable for wide range of applications where is the material subjected to different modes of loading and different loading rates. This paper deals with measurement of the Ultra high performance concrete reinforced with steel fibres in quasi-static compression mode of deformation and two elevated strain rates using split Hopkinson pressure bar. The results of the measurement show high increase of the mechanical properties with elevated strain rate.
DOI:
10.14311/APP.2023.42.0051
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.
Publikováno:
2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 109-112), ISBN 978-80-86246-51-2, ISSN 1805-8256
Anotace:
Stress uniformity in a specimen represents a crucial parameter for validity of impact experiment conducted in a split Hopkinson bar. Principle of the experimental method is to measure elastic stress waves that propagate in the bars of an experimental setup and to calculate stress to strain relations at the interfaces with the specimen. However, standard procedure to evaluate the experiment can only be valid when stress is distributed approximately uniformly along the specimen. As the stress wave has to propagate through the specimen during the experiment, a time period of significantly non-uniform stress distribution is present and a certain number of wave transits is required to achieve approximately uniform stress distribution. In this paper, a simple analytical model assuming one-dimensional wave propagation theory, non-equal mechanical impedance of the bars and linear elastic material model of the specimen is introduced to determine a number of transits required to achieve uniform stress distribution in the specimen. Potential of the calculated results is discussed in an experiment using a direct impact Hopkinson bar and a material with significant plateau in its stress-strain response.
DOI:
10.21495/512109
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; Ing. Václav Rada; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 107-107)
Anotace:
Additively manufactured materials represent an advanced type of engineering material allowing for rapid building of parts with complex design. Additively manufactured metallic materials are particularly promising for application in high-tech industry, requiring optimized parts with complex shape and high performance mechanical properties. In this contribution, the cylindrical specimens manufactured from 316L powdered stainless steel built in different orientations to the printing platform are subjected to compression at high strain rates using split Hopkinson pressure bar (SHPB). The specimens are subjected to quasi- static and dynamic compression at strain rates ranging from 1500/s to 5000/s. Changes in damage development and failure mode are investigated through combination of high speed optical imaging with data of the SHPB instrumentation. For the testing, the SHPB with high strength aluminum alloy bars, soft copper pulse shapers and two sizes of the striker bar is used. The bars are instrumented with a set of foil strain-gauges. The experiments are observed by stateof-the-art high speed camera with frame rate of approximately 250kfps. The camera is time synchronized with the data acquisition system. Strain localization and changes in failure mode related to the printing orientation and strain rate, particularly occurrence of the fatal macroscopic crack and identification of the corresponding failure strain, are investigated using digital image correlation (DIC). It is found out that the failure mode changes dramatically with the increasing strain rate resulting in sudden and complete failure of the specimen during high strain rate compression. The failure is dependent on both the printing orientation and the strain rate.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 85-88), ISBN 978-80-86246-51-2, ISSN 1805-8256
Anotace:
In this study, the relation between the presence of the filler in different types of open auxetic lattices and their Poisson’s functions was investigated using optical strain measurement technique and Digital Image Correlation (DIC) algorithms. Three different types of auxetics were manufactured using Selective Laser Sintering (SLS) technique from 316L–040 stainless steel alloy: (i) 2D re-entrant, (ii) 3D re-entrant and (iii) 2D missing rib structure. All types of SLS printed auxetics were then divided into three different groups according to the presence of the filler: (a) unfilled and filled with (b) porous polyurethane foam and (c) ordnance gelatin. All groups of sam- ples were tested in uniaxial compression mode under both quasi-static and high strain rates in the range of thousands strains per second using the Split Hopkinson pressure bar. During the loading tests, the deforming structure was observed optically and from the captured image data, the in-plane displacements were calculated using DIC. Based on these displacements, Poisson’s functions among the tested groups were compared. The results show that in the case of both types of polymeric fillers, the auxetic behaviour is suppressed with increasing values of longitudinal strain.
DOI:
10.21495/51285
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.
Publikováno:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems)
Anotace:
The problem of the linear elastodynamics including domain decomposition via localized Lagrange multipliers method [2] is solved using finite element method and direct time integration. Time integration of domains is performed separately with different time steps with integer ratio. The known asynchronous integrator scheme [1] is generalized for multiple domains problem and enhanced by the use of a local variant of the pushforward-pullback method, which effectively avoids spurious oscillation in steep stress pulses response. The proposed method is applied to the rectangular step pulse propagation problem considering the linearly varying Young modulus in space as well as the bi-material interface problem. To prove the robustness and the accuracy, the comparison with analytical solution and commercial software outputs is provided.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Park, K.C.
Publikováno:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 35-35)
Anotace:
The problem of the linear elastodynamics including domain decomposition via localized La- grange multipliers method [2] is solved using finite element method and direct time integration. Time integration of domains is performed separately with different time steps with integer ra- tio. The known asynchronous integrator scheme [1] is generalized for multiple domains prob- lem and enhanced by the use of a local variant of the pushforward-pullback method, which effectively avoids spurious oscillation in steep stress pulses response. The proposed method is applied to the rectangular step pulse propagation problem considering the linearly varying Young modulus in space as well as the bi-material interface problem. To prove the robustness and the accuracy, the comparison with analytical solution and commercial software outputs is provided.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Felten, M.; Fries, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Publikováno:
2022, Advanced Engineering Materials, 24 (3), ISSN 1438-1656
Anotace:
Open-cell metal foams are a versatile class of porous lightweight materials, which are predominantly used as kinetic energy absorbers in a wide scope of applications. Based on their bio-inspired inhomogeneous 3D porous structure, they are capable to significantly reduce the mass of structural designs. Starting with a polyurethane (PU) template foam, the specimens in the present contribution are manufactured by an electrochemical nickel (Ni) deposition. This manufacturing process is beneficial regarding both the specimen design and the adjustment of mechanical properties correlated with the Ni-coating thickness. Herein, the strain-rate sensitivity of open-cell Ni/PU hybrid metal foams is investigated by quasistatic compression tests and high-velocity impact tests conducted with a conventional split-Hopkinson pressure bar device.
DOI:
10.1002/adem.202100872
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Jan Falta; Ing. Veronika Drechslerová; Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2022, International Conference on Nonlinear Solid Mechanics, abstract book, International Research Center on Mathematics and Mechanics of Complex Systems), p. 104-104)
Anotace:
The mechanical response of sandwich panels tailored to specific applications investigated becomes an extensively topic for research teams. Sandwich panels typically consist of a lightweight core (porous materials, meta-materials structures) and covering shell (solid or composite layer). These materials can be used as, e.g., the main component of crumple zones in vehicles or low-velocity protection in many applications, due to their high specific energy absorption and low density. An unique loading mode in dynamic mechanical testing is a dynamic indentation where combining multi-directional stress distribution in sandwich panels is not an easy task for description. The main aim of this work is to compare sandwich panels with two different types of core (3D inverted honeycomb and conventional honeycomb structures with similar specific densities). Based material of the aforementioned cores is photopolymer resin which allows the manufacturing of complex shapes of cores by stereolithography technology. All specimens, equipped with a spreading thin layer of polyethylene shell, are subjected to dynamic penetration to evaluate the mechanical behavior, penetration resistance, and energy-absorbing capability at different impact velocities. An in-house developed direct impact Hopkinson bar is used for dynamic indentation experiments. The loading apparatus is equipped with strain gauges and the measured signals are used for the calculation of an applied force and impact velocity. A pair of highspeed cameras are used for optical inspection of the experiments. A targeted camera is used for evaluating the velocity of the projectile using the digital image correlation method (DIC) for comparison with strain-gauge measurement, and an overview camera is used for capturing the surroundings of the impact plane.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2022, ENGINEERING MECHANICS 2022, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 285-288), ISBN 978-80-86246-51-2, ISSN 1805-8256
Anotace:
Research into the mechanical behaviour of lattice structures and metal foams at high strain rates using experiments based on a direct impact Hopkinson bar (DIHB) method has been recently proposed to overcome several limitations of the conventional split Hopkinson pressure bar (SHPB). Especially, the socalled open Hopkinson pressure bar (OHPB), a modification of DIHB with strain measurement points on both bars, has been proved to be a suitable experimental technique for testing of materials with low mechanical impedance. However, experimental testing is usually limited in terms of resources and, hence, it is convenient to employ numerical methods to predict the results of experiments and, if necessary, adjust the parameters of the experimental procedure based on the preceding numerical analysis of the problem. Developing a numerical model of the whole experimental set-up is, thus, a key method to achieve a reliable analysis. In this paper, we present a numerical model of an OHPB apparatus and demonstrate its suitability for inverse numerical simulations of the closed-cell aluminium foam.
DOI:
10.21495/51-2-285
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. et Ing. Radim Dvořák; Ing. Michaela Jurko; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2022, Dynamic Behaviour of Additively Manufactured Structures & Materials, Freiburg im Breisgau, Albert-Ludwigs-Universität Freiburg), p. 187-192)
Anotace:
We demonstrate numerical modelling of the mechanical response of auxetic structures sub- jected to dynamic uniaxial compressive load- ing in split Hopkinson pressure bar (SHPB) at the strain rates of 1500 s−1 and 3000 s−1. The stress-strain characteristics as well as com- pressive strain dependent Poisson’s ratio of re-entrant honeycomb and missing-rib aux- etic lattices are assessed in LS-DYNA simula- tions with explicit time integration. Numer- ical results are supported by SHPB experi- ments utilized for both calibration of finite el- ement modeling and verification of the sim- ulations. The studied lattices were additively manufactured by laser powder bed fusion from 316L stainless steel. The numerical aspects of the simulations together with the influence of the 3D printing quality on the reliability of the results are discussed.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Michaela Jurko; Ing. Václav Rada; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2022, Dynamic Behaviour of Additively Manufactured Structures & Materials, Freiburg im Breisgau, Albert-Ludwigs-Universität Freiburg), p. 103-110)
Anotace:
Open Hopkinson Pressure Bar (OHPB) appa- ratus is used, together with conventional split Hopkinson pressure bar (SHPB), for dynamic testing of additively manufactured cellular me- tamaterials at intermediate and high strain rates. Benefits of the OHPB testing method over standard established methods are dis- cussed. The investigated metamaterials in- clude various types of auxetic lattices manu- factured from powdered austenitic steel by powder bed fusion technology. It is found out that the investigated type of metamate- rials exhibits significant strain rate sensitivity of the stress-strain curves as well as of the apparent auxeticity. Moreover, its deforma- tion mechanism changes with the increasing impact velocity as the buckling of the individ- ual struts is reduced by the inertia effects.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Václav Rada; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Mauko, A.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2022, Materials, 15 (3), ISSN 1996-1944
Anotace:
The main aim of the study was to analyse the strain rate sensitivity of the compressive deformation response in bulk 3D-printed samples from 316L stainless steel according to the printing orientation. The laser powder bed fusion (LPBF) method of metal additive manufacturing was utilised for the production of the samples with three different printing orientations: 0◦, 45◦, and 90◦. The specimens were experimentally investigated during uni-axial quasi-static and dynamic loading. A split Hopkinson pressure bar (SHPB) apparatus was used for the dynamic experiments. The experiments were observed using a high-resolution (quasi-static loading) or a high-speed visible-light camera and a high-speed thermographic camera (dynamic loading) to allow for the quantitative and qualitative analysis of the deformation processes. Digital image correlation (DIC) software was used for the evaluation of displacement fields. To assess the deformation behaviour of the 3D-printed bulk samples and strain rate related properties, an analysis of the true stress–true strain diagrams from quasi-static and dynamic experiments as well as the thermograms captured during the dynamic loading was performed. The results revealed a strong strain rate effect on the mechanical response of the investigated material. Furthermore, a dependency of the strain-rate sensitivity on the printing orientation was identified.
DOI:
10.3390/ma15030941
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Ing. Václav Rada; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2021, Metals — Open Access Metallurgy Journal, 11 (8), ISSN 2075-4701
Anotace:
Compressive deformation behaviour of additively manufactured lattice structures based on re-entrant tetrakaidecahedral unit-cell geometry were experimentally investigated under quasi-static and dynamic loading conditions. Specimens of four different structures formed by three-dimensional periodical assembly of selected unit-cells were produced by a laser powder bed fusion technique from a powdered austenitic stainless steel SS316L. Quasi-static compression as well as dynamic tests using split Hopkinson pressure bar (SHPB) apparatus at two strain-rates were conducted to evaluate the expected strain-rate sensitivity of the fundamental mechanical response of the structures. To evaluate the experiments, particularly the displacement fields of the deforming lattices, optical observation of the specimens using a high-resolution camera (quasi-static loading) and two synchronised high-speed cameras (SHPB experiments) was employed. An in-house digital image correlation algorithm was used in order to evaluate the anticipated auxetic nature of the investigated lattices. It was found that neither of the investigated structures exhibited auxetic behaviour although strain-rate sensitivity of the stress–strain characteristics was clearly identified for the majority of structures.
DOI:
10.3390/met11081196
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Mauko, A.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; Ing. Václav Rada; Ing. Michaela Jurko; doc. Ing. Petr Zlámal, Ph.D.; Vesenjak, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ren, Z.
Publikováno:
2021, Metals — Open Access Metallurgy Journal, 11 (1), ISSN 2075-4701
Anotace:
The mechanical behaviour of three different auxetic cellular structures, hexa-chiral 2D, tetra-chiral 2D and tetra-chiral 3D, was experimentally investigated in this study. The structures were produced with the powder bed fusion method (PBF) from an austenitic stainless steel alloy. The fundamental material mechanical properties of the sample structures were determined with classic quasi-static compressive tests, where the deformation process was captured by a high-resolution digital camera. The Split Hopkinson Pressure Bar (SHPB) apparatus was used for dynamic impact testing at two impact velocities to study the strain-rate dependency of the structures. Two synchronised high-speed cameras were used to observe the impact tests. The captured images from both quasi-static and dynamic experiments were processed using a custom digital image correlation (DIC) algorithm to evaluate the displacement/strain fields and the Poisson’s ratio. Predominant auxetic behaviour was observed in all three structures throughout most of the deformation process both under quasi-static and impact loading regimes. The tetra-chiral 2D structure showed the most significant auxetic behaviour. Significant stress enhancement in all tested structures was observed in dynamic testing. The Poisson’s ratio strain-rate dependency was confirmed for all three auxetic structures.
DOI:
10.3390/met11010052
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Václav Rada; Adorna, M.; Bronder, S.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2021, International Journal of Impact Engineering, 148, ISSN 0734-743X
Anotace:
Direct impact testing with a Hopkinson bar is, nowadays, a very popular experimental technique for investigating the behavior of cellular materials, e.g., lattice metamaterials, at high strain-rates as it overcomes several limitations of the conventional Split Hopkinson Pressure Bar (SHPB). However, standard direct impact Hopkinson bars (DIHB) have only single-sided instrumentation complicating the analysis. In this paper, a DIHB apparatus instrumented with conventional strain-gauges on both bars (a so called Open Hopkinson Pressure Bar - OHPB) is used for dynamic impact experiments of cellular materials. Digital image correlation (DIC) is used as a tool for investigating the displacements and velocities at the faces of the bars. A straight-forward wave separation technique combining the data from the strain-gauges with the DIC is adopted to increase the experiment time window multiple times. The experimental method is successfully tested at impact velocities in a range of 5-30 m/s with both linear elastic and visco-elastic bars of a medium diameter. It is shown that, under certain circumstances, a simple linear elastic model is sufficient for the evaluation of the measurements with the visco-elastic bars, while no additional attenuation and phase-shift corrections are necessary. The applicability of the experimental method is demonstrated on various experiments with conventional metal foams, hybrid foams, and additively manufactured auxetic lattices subjected to dynamic compression.
DOI:
10.1016/j.ijimpeng.2020.103767
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Adorna, M.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Glinz, J.; Ing. Michaela Jurko; Ing. Tomáš Doktor, Ph.D.; Mauko, A.; doc. Ing. Daniel Kytýř, Ph.D.; Vesenjak, M.; Duarte, I.; Ren, Z.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2021, Materials Science and Engineering A - Structural Materials: Properties, Microstructure and Processing, 800, ISSN 0921-5093
Anotace:
Light-weight cellular solids, such as aluminium foams, are promising materials for use in ballistic impact mitigation applications for their high specific deformation energy absorption capabilities. In this study, three different types of aluminium alloy based in-house fabricated cellular materials were subjected to dynamic penetration using the in-house experimental setup to evaluate their deformation and microstructural response. Two-sided direct impact Hopkinson bar apparatus instrumented with two high-speed cameras observing the impact area and the penetrated surface of the specimens was used. Advanced wave separation technique was employed to process strain-gauge signals recorded during penetration. Images captured by one of the cameras were processed using an in-house Digital Image Correlation method with sub-pixel precision, that enabled validation of the wave separation results of the strain-gauge signals. The second camera was used to observe the penetration into the tested specimens for correct interpretation of the measured signals with respect to derived mechanical and microstructural properties at different impact velocities. Differential X-ray computed tomography of selected specimens was performed, which allowed for an advanced pre- and post-impact volumetric analysis. Results of performed experiments and elaborate analysis of the measured experimental data are shown in this study.
DOI:
10.1016/j.msea.2020.140096
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Bronder, S.; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Publikováno:
2021, Advanced Engineering Materials, 23 (5), p. 1-15), ISSN 1438-1656
Anotace:
With their increased energy absorption capacity, auxetic materials are perfectly fit to develop new, enhanced lightweight crash absorbers for cars. Herein, the mass distribution along the struts is optimized via finite element analysis with a parameterized optimization. Four different auxetic unit cells are taken from the literature and their struts parameterize, the models simulate, and the mass specific energy absorption capacity optimizes. The two models with the highest energy absorption capacity are then selected for experimental investigation and produced by additive manufacturing from a polymer. To further enhance the mechanical properties, the specimens are electrochemically coated with nickel and the polymer molten out by pyrolysis. Those Ni/polymer hybrids are subjected to quasistatic and dynamic impact experiments. Only a small strain rate sensitivity can be detected under dynamic loading, namely, a higher plastic collapse and higher plateau stress. The hollow struts are folding instead of bending, which render them much weaker than predicted by the simulation. In conclusion, it is possible to improve existing crash absorber elements with tailored auxetic hybrid structures. They absorb higher amounts of energy without changing their stiffness under dynamic loading while saving mass and cost.
DOI:
10.1002/adem.202001393
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Michaela Jurko; Mauko, A.; Valach, J.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2021, Advanced Engineering Materials, 23 (1), ISSN 1438-1656
Anotace:
Metamaterials produced using additive manufacturing represent advanced structures with tunable properties and deformation characteristics. However, the manufacturing process, imperfections in geometry, properties of the base material as well as the ambient and operating conditions often result in complex multiparametric dependence of the mechanical response. As the lattice structures are metamaterials that can be tailored for energy absorption applications and impact protection, the investigation of the coupled thermomechanical response and ambient temperature‐dependent properties is particularly important. Herein, the 2D re‐entrant honeycomb auxetic lattice structures additively manufactured from powdered stainless steel are subjected to high strain rate uniaxial compression using split Hopkinson pressure bar (SHPB) at two different strain rates and three different temperatures. An in‐house developed cooling and heating stages are used to control the temperature of the specimen subjected to high strain rate impact loading. Thermal imaging and high‐speed cameras are used to inspect the specimens during the impact. It is shown that the stress–strain response as well as the crushing behavior of the investigated lattice structures are strongly dependent on both initial temperature and strain rate.
DOI:
10.1002/adem.202000669
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Fíla, Ph.D.; Kolman, R.; Ren, Z.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2020
Anotace:
This doctoral thesis is focused on the experimental analysis of cellular meta-materials subjected to a dynamic impact with a high strain-rate. In particular, additively manufactured auxetic lattices (structures with a negative Poisson’s ratio) are investigated. Two in-house Hopkinson bar experimental setups are developed for the testing of the structures: i) a conventional Split Hopkinson Pressure Bar (SHPB, Kolsky bar), and ii) a novel direct impact Open Hopkinson Pressure Bar (OHPB). Both setups are tailored for the application on the low impedance materials and are used for the experiments subjecting the cellular meta-materials to a high strain-rate uni-axial compression. In the thesis, the developed apparatuses, the instrumentation, evaluation methods and the experimental program are described in detail. The experiments are optically inspected using several high-speed cameras and a digital image correlation technique is employed for the advanced analysis of the deformation behavior of the meta-materials. Using the data from several experimental campaigns, the strain-rate sensitivity of the selected auxetic lattices and their Poisson’s ratio is investigated in detail. It is found out that the auxetic structures are, in general, strain-rate sensitive and their Poisson’s ratio is both strain-rate and strain dependent. Other representative results exploiting the deformation behavior of cellular materials, e.g., hybrid open-cell foams and hybrid hollow strut auxetic lattices are also presented in the study.
Typ:
Disertační práce (PhD)

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 17-20), ISBN 978-80-01-06670-6, ISSN 2336-5382
Anotace:
Presented paper deals with experimental study on compressive properties of auxetics with controlled stiffness of strut joints. The variable strut joints properties were simulated by adding extra amount of material in the struts’ intersection regions. Four groups of inverted honeycomb structures were prepared by multi-jet 3D printing and tested in quasi-static compression. The structure collapsed gradually, however after the first collapse, failure in entire cross-section occurred due to the brittle nature of the base material. The behavior up to the first collapse was consistent among the specimens within each group, while differed slightly subsequently. With higher reinforcement in the joints, results showed increasing stress at the first collapse (ultimate compressive stress) while the strain at the first collapse remained unchanged. The auxetic behaviour became less significant with increasing joints’ reinforcement.
DOI:
10.14311/APP.2019.25.0017
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Luksch, J.; Felten, M.; Fries, M.; Jung, A.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, International Conference on Nonlinear Solid Mechanics - ICoNSoM2019, Palazzo Argiletum, Roma, Italy), p. 131-131)
Anotace:
Cellular solids, such as metal foams, hybrid foams, 3D printed lattices or additively manufactured auxetic structures are complex lightweight cellular materials with high energy absorption capabilities and possible functionally graded material properties. Engineering applications of such materials require optimization of their design, and thus their mechanical behavior under the representative loading conditions (i. e., dynamic impact, blast). The design and optimization procedures require a relevant material model based on the experimental investigation of the constructs. In this study, the application of the Digital Image Correlation (DIC) technique on the cellular solids in quasi-static and dynamic compression is discussed and the representative results of the method in this application are presented. Here, digital image correlation is used as an advanced method for the complex experimental analysis of the displacement and strain fields of several cellular solids under quasi-static compression and high strain-rate loading using the Split Hopkinson Pressure Bar (SHPB) apparatus. The data from the experiments with the specimens of the selective laser sintered auxetic lattices, made of powdered austenitic steel, and with hybrid nickel-polyurethane aluminum foam were processed using a custom digital image correlation tool. Results covering the evaluation of the displacement and strain fields, different methods for evaluation of Poisson’s ratio, and the analysis of the digital image correlation reliability are presented in the study. The study is focused particularly on the application of the digital image correlation on the data captured by a high-speed camera during high strain-rate experiments and the analysis of the cellular solids during dynamic impact. Comparison of the digital image correlation results with the other methods, its limitations and the actual challenges in this field are also discussed in the study.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. Jan Falta; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 32-35), ISBN 978-80-01-06670-6, ISSN 2336-5382
Anotace:
The presented paper is focused on embedding of the serially manufactured piezo-electric impact load-cell into Split Hopkinson Pressure Bar (SHPB) for a direct force measurement during dynamic loading. Conventionally, during the SHPB test dynamic force equilibrium is investigated by a comparison of the transmitted signal wave and the difference between the incident and reflected signals waves to the incident bar, measured by strain gauges \cite{bib1}. However, in the experiments with specimens with low \linebreak mechanical impedance, a major portion of the incident wave is reflected back on the boundary between the bar and the specimen. Comparison between two-large amplitude incident and reflected pulse and \linebreak a small-amplitude transmitted pulse can be influenced by large error and resulting force equilibrium can be inaccurate. Therefore, a piezo-electric quartz impact force transducer was used to directly measure the axial forces in the vicinity of the specimen end surfaces, allowing to analyze the force equilibrium which is an essential characteristic for reliable measurement. Measured values from strain gauges were compared with values obtained from force transducer, to verify the validity of the acquired signals which will increase the reliability of the measured data. The presented solution will help to determine the mechanical properties of advanced materials which is necessary for investigation of complex modern material structures behaviour.
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Adorna, M.; Bronder, S.; Ing. Jan Falta; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 1-5), ISBN 978-80-01-06670-6, ISSN 2336-5382
Anotace:
Three different tools for Digital Image Correlation (DIC) were used for evaluation of dynamic experiments performed using custom Open Hopkinson Pressure Bar (OHPB) apparatus. High strain-rate measurements were performed on specimens of advanced cellular materials with predefined structure and negative Poisson's ratio. Low impedance polymethyl methacrylate (PMMA) bars instrumented with foil strain-gauges were used for dynamic loading of the specimens. Experiments were observed using a pair of high-speed cameras for imaging of loading process in sufficient quality. Custom developed evaluation DIC tool implemented in Matlab, open-source Matlab tool (NCorr) and commercial DIC software (ISTRA 4D) were all used for evaluation of image sequences recorded by high-speed cameras. Comparison of results obtained using all three different DIC tools and results of complementary strain-gauge measurement are shown in this paper. Verification of reliability of custom made DIC software tool is presented.
DOI:
10.14311/APP.2019.25.0001
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 21-24), ISBN 978-80-01-06670-6, ISSN 2336-5382
Anotace:
In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the filling material were tested, (i) ordnance gelatin, (ii) low expansion polyurethane foam, and (iii) polyurethane putty. To evaluate their impact energy absorption bulk samples of the selected materials were tested in compression loading mode at strain-rates 1000 s−1 to 4000 s−1 . The high strain-rate compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was equipped with PMMA bars to enable testing of cellular materials with low mechanical impedance. Based on the comparative measurement response to compression at both low and high strain-rates was analysed. The results show a significant strain-rate sensitivity of the ordnance gelatin and of the polyurethane putty, while strain-rate effect in the polyurethane foam was not observed.
DOI:
10.14311/APP.2019.25.0021
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Bronder, S.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Adorna, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Publikováno:
2019, Temperature dependence of material behaviour at high strain-rate, Politecnico di Torino), ISBN 978-88-85745-27-8
Anotace:
Two types of the hybrid polymer-nickel auxetic specimens were subjected to the quasi-static compression and compressive impact loading using Open Hopkinson Pressure Bar. Two variants of the 3D re-entrant auxetic lattice were used: i) structures with rectangular struts and ii) structure with rounded struts. The specimens were numerically optimized, prepared using computer aided design, and the base constructs were 3D printed from VisiJet EX200 polymer. The constructs were then coated using the electrodeposition of the nanocrystalline nickel in two nominal thicknesses of the coating (60 μm and 120 μm). After the coating process, the core part of the constructs was removed by the burning-out of the polymer at elevated temperature. The structures were subjected to the quasi-static compression and simultaneously inspected using an CCD camera, while Hopkinson bar was used for the impact loading of the specimens at two different impact velocities (ca. 5 m/s and 26 m/s). Dynamic experiments were observed with a pair of high-speed cameras and an infrared camera. The high-speed camera images were processed using a custom digital image correlation algorithm. Mechanical as well as thermal behavior of the hybrid auxetic structures subjected to the different loading conditions was analyzed and summarized in this paper.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. et Ing. Radim Dvořák; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 25-31), ISBN 978-80-01-06670-6, ISSN 2336-5382
Anotace:
The paper aims at the numerical simulation of the wave propagation in compressive Split Hopkinson Pressure Bar (SHPB) experiment. The paper deals with principles of SHPB measurement, optimisation of a numerical model and techniques of pulse shaping. The parametric model of the typical SHPB configuration developed for LS-DYNA environment is introduced and optimised (in terms of element size and distribution) using the sensitivity study. Then, a parametric analysis of a geometric properties of the pulse shaper is carried out to reveal their influence on a shape of the incident pulse. The analysis is algorithmized including the pre- and post-processing routines to enable automated processing of numerical results and comparison with the experimental data. Results of the parametric analysis and the influence of geometric properties of the pulse shaper (diameter, length) on the incident wave are demonstrated.
DOI:
10.14311/APP.2019.25.0025
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2019, Engineering Mechanics 2019: Book of full texts, Prague, Institute of Thermomechanics, AS CR, v.v.i.), p. 97-101), ISBN 978-80-87012-71-0, ISSN 1805-8248
Anotace:
In this paper, an implementation of Split Hopkinson Pressure Bar (SHPB) and its modification Open Hopkinson Pressure Bar (OHPB) for testing of cellular structures is presented. Dynamic testing of materials with low mechanical impedance is very demanding in terms of achieving the requested experimental device performance. Key elements of the Hopkinson bar instrumentation that were successfully employed in dynamic testing of cellular materials are presented in this paper. Detailed overview of the strain-gauges instrumentation including our best practices for installation and noise reduction is provided. Information about the instrumentation of Hopkinson bar with high-speed cameras are also given. To demonstrate the performance of the proposed instrumentation some examples of a typical results are summarized in the text.
DOI:
10.21495/71-0-97
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Adorna, M.; Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2019, Engineering Mechanics 2019: Book of full texts, Prague, Institute of Thermomechanics, AS CR, v.v.i.), p. 29-33), ISBN 978-80-87012-71-0, ISSN 1805-8248
Anotace:
In this paper, digital image correlation method (DIC) is introduced as a tool for evaluation of high strain-rate experiments perfomed using Hopkinson Bar apparatus. Samples of advanced cellular materials with predefined periodic structure and negative Poisson’s ratio (auxetic structures) were investigated in this study. In-house Hopkinson Pressure Bar apparatus was used to perform the impact experiments and the experimental setup was observed using a pair of high-speed cameras. Custom DIC software tool was used to evaluate highspeed cameras records. Selected representative results of DIC applications on Hopkinson Bar experiments are provided in this paper.
DOI:
10.21495/71-0-29
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.; Luksch, J.; Ing. Michaela Jurko; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, Advanced Engineering Materials, 21 (8), ISSN 1438-1656
Anotace:
This paper deals with experimental investigation into a strain‐rate dependent function of Poisson's ratio of three auxetic structures subjected to compressive loading. The missing rib, the 2D re‐entrant honeycomb, and the 3D re‐entrant honeycomb lattices printed using selective laser sintering from powdered SS316L austenitic steel are investigated. The samples are subjected to uni‐axial compression under quasi‐static conditions and dynamic conditions using the Split Hopkinson Pressure Bar (SHPB). The deforming specimens are optically observed in order to apply a digital image correlation for evaluation of the in‐plane displacement and strain fields. From the calculated strain fields, the function of Poisson's ratio is calculated for each experiment using different methods taking specific regions of interest of the specimen microstructures into account. The obtained functions of Poisson's ratio are plotted for each microstructure and strain‐rate. The analysis of the results shows that the strain‐rate has a significant influence on the deformation characteristics of all the investigated microstructures yielding differences in the magnitude of the minima of Poisson's ratio and the differences in the maximum overall compressive strain, where the lattices are still auxetic.
DOI:
10.1002/adem.201900204
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2019, 17th YOUTH SYMPOSIUM ON EXPERIMENTAL SOLID MECHANICS, Praha, Česká technika - nakladatelství ČVUT), p. 68-72), ISBN 978-80-01-06670-6, ISSN 2336-5382
Anotace:
The paper is focused on evaluation of the relation between mechanical properties of 3D printed stainless steel 316L-0407 and printing direction (i.e. the orientation of the part which is being printed in the manufacturing device) subjected to compressive loading at different strain-rates. In order to evaluate the strain rate dependency of the 3D printed material’s compressive characteristics, dynamic and quasi-static experiments were performed. Three sets of bulk specimens were produced, each having a different printing orientation with respect to the powder bed plane (vertical, horizontal and tilted). To assess the deformation behaviour of the 3D printed material, compressive stress-strain diagrams and compressive yield strength and tangent modulus were evaluated.
DOI:
10.14311/APP.2019.25.0068
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.; Ing. Petr Koudelka, Ph.D.; Ing. Michaela Jurko; Luksch, J.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, 10th International Conference Auxetics and other materials and models with ”negative” characteristics - abstract book, Poznań, Institute of Molecular Physics), p. 37-39), ISBN 978-83-933663-8-5
Anotace:
n this work, selective laser sintered (SLS) auxetic lattices printed from the powdered 316L–0407 austenitic steel were subjected to compressive loading at several strain-rates. Three types of the auxetic lattices were tested: i) 2D re-entrant honeycomb, ii) 2D missing rib, and iii) 3D re-entrant honeycomb. The structures were subjected to the quasi-static uni-axial compression using a standard electromechanical loading device. The experiments were observed using a CCD camera. In dynamic experiments, the specimens were compressed at four different strain-rates using two Hopkinson bar techniques. Data recorded by the strain-gauges mounted on the measurement bars were used for evaluation of the mechanical behavior of the specimen (e. g., stress-strain and strain-rate-strain diagrams). A custom digital image correlation (DIC) tool based on Lucas-Kanade tracking algorithm was used for the advanced analysis of the displacement and strain fields in the specimens of both quasi-static and dynamic experiments. At least 5 specimens of the each structure were tested per one strain-rate to ensure a sufficient statistics and relevancy of the results.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Mauko, A.; Adorna, M.; Ing. Michaela Jurko; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, Temperature dependence of material behaviour at high strain-rate, Politecnico di Torino), ISBN 978-88-85745-27-8
Anotace:
Specimens based on re-entrant honeycomb auxetic lattice were printed from powdered austenitic steel using selective laser sintering and subjected to dynamic compression using Split Hopkinson Pressure Bar (SHPB). To study the influence of strain-rate and temperature on mechanical properties of the lattices, heating and cooling devices integrated into the SHPB apparatus were developed and the experiments were performed at two different strain rates given by different striker impact velocities. As a result, the dynamic compression was performed at two strain rates and three temperature levels (reduced, room, and elevated temperature) with 5 specimens for each combination. The specimen were observed by a pair of high-speed CMOS optical cameras and a high-speed thermal imaging camera. Optical cameras were used for evaluation of strain fields of the compressed samples using digital image correlation and for inspection of experiment validity. Thermograms were used for qualitative evaluation of heat distribution within the sample microstructure during its deformation. It has been found out that increase of strain-rate results in increase of plateau stress together with decrease of densification strain. The difference in specimen temperature led to changes in the mechanical properties, the absolute temperature of the fully compressed sample and increase of maximum measured temperature during the experiment.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Adorna, M.
Publikováno:
2018, The 2nd International Conference of Wave Propagation in Solids - Book of abstracts, Praha, Ústav termomechaniky AV ČR, v. v. i.), p. 43-44), ISBN 978-80-87012-67-3
Anotace:
In this contribution, an Open Hopkinson Pressure Bar (OHPB) apparatus was used for high strain-rate compression of the additively manufactured auxetic lattices and selected cellular metals. The principle of OHPB is based on Direct Impact Hopkinson Bar (DIHB). Instead of striker bar, the incident bar is accelerated in the gas-gun and it hits directly the specimen mounted on the face of the transmission bar. The incident bar is instrumented using strain-gauges and so, in contrast with Taylor anvil test, strain histories corresponding to the both contact faces of the specimen are measured and thus are known. Unlike conventional SHPB test, OHPB allows for high maximum strain in the specimen at constant strain-rate with good conditions of dynamic equilibrium as the strain waves propagate from the specimen boundaries.
Typ:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 44-47), ISBN 978-80-01-06474-0, ISSN 2336-5382
Anotace:
An experimental study on energy absorption capabilities and strain rate sensitivity of ordnance gelatine was performed. Strain energy density under quasi static compression and moderate strain rate impact tests was compared. In the study two types of material were tested, bulk ordnance gelatine and polymeric open-cell meshwork filled with ordnance gelatine. From the results a significant strain-rate effect was observed in terms of ultimate compressive strength and strain energy density. In comparison of the deformation behaviour under quasi static conditions and drop weight test the difference was very significant, however slight increase in both strength and strain energy density was observed even between different impact energies and velocities during the impact testing. The peak acceleration was significantly reduced in polymer meshwork filled by gelatine in comparison to the bulk gelatine.
DOI:
10.14311/APP.2018.18.0044
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Adorna, M.
Publikováno:
2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 10-14), ISBN 978-80-01-06474-0, ISSN 2336-5382
Anotace:
This paper presents an overview of the custom design instrumentation of a Split Hopkinson Pressure Bar modified for dynamic testing of materials with low mechanical impedance, particularly for cellular metallic materials (e. g. metal foams, laser sintered structures). Design and implementation of the components related to the strain wave measurement based on strain gauges (i.e. strain-gauge measurement unit, power supply unit, filtration) and the components used for the control and synchronization of the experiment, such as module of laser trough-beam photoelectric sensor are summarized in the paper. Aside from the design of the hardware components, the contribution deals also with development of a control software with graphical user interference using LabView (National Instruments, USA) programming environment, that allows selection of parameters of the dynamic tests and their storage for the evaluation of experiments.
DOI:
10.14311/APP.2018.18.0010
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Václav Rada; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Petr Koudelka, Ph.D.
Publikováno:
2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 15-19), ISBN 978-80-01-06474-0, ISSN 2336-5382
Anotace:
In recent years, open-source applications have replaced proprietary software in many fields. Especially open-source software tools based on Linux operating system have wide range of utilization. In terms of CNC solutions, an open-source system LinuxCNC can be used. However, the LinuxCNC control software and the graphical user interface (GUI) could be developed only on top of Hardware Abstraction Layer. Nevertheless, the LinuxCNC community provided Python Interface, which allows for controlling CNC machine using Python programming language, therefore whole control software can be developed in Python. The paper focuses on a development of a multi-process control software mainly for in-house developed loading devices operated at our institute. The software tool is based on the LinuxCNC Python Interface and Qt framework, which gives the software an ability to be modular and effectively adapted for various devices.
DOI:
10.14311/APP.2018.18.0015
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Adorna, M.; Ing. Jan Falta; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 77-81), ISBN 978-80-01-06474-0, ISSN 2336-5382
Anotace:
This work presents a data preprocessing procedure for signal acquired during high strain-rate loading using a custom Split Hopkinson Pressure Bar (SHPB). Before the evaluation of the experimental data, preprocessing of the measured signals including application of suitable digital or analog filter needs to be performed. Our department mainly focuses on measurements performed on advanced materials (e.g. materials with predefined structures or hybrid foams). For such measurements, it is essential to perform data preprocessing and apply suitable filter, to be able to appropriately determine deformation pulses on the measuring bars. This paper focuses foremost on spectral analysis of the measured signals, and design of optimal method of data filtering. Data from several different SHPB experiments were processed and results of different filtering methods are shown in this paper. Parameters of the best performing filter were optimized and shown to be universal for wide range of SHPB measurements.
DOI:
10.14311/APP.2018.18.0077
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.
Publikováno:
2018, Engineering Mechanics 2018: Book of Full Texts, Praha, Ústav teoretické a aplikované mechaniky AV ČR, v. v. i.), p. 213-216), ISBN 978-80-86246-88-8, ISSN 1805-8248
Anotace:
In this paper, a simple analytic model of Split Hopkinson Pressure Bar (SHPB) propelled by gas-gun is introduced. The model allows for prediction of the output of SHPB experiment or can be used inversely as a design tool for gas-gun propelled SHPB. The model is based on existing models of light gas-gun working according to adiabatic process and on one-dimensional wave propagation theory in linear elastic cylindrical slender bar. The model allows for calculation with elementary drag effects. Model functionality was evaluated and compared with the experimental results of a SHPB setup equipped with linear elastic (aluminium) bars and visco-elastic (polymethyl metacrylate) bars at two different impact velocities.
DOI:
10.21495/91-8-213
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Adorna, M.; Luksch, J.; Ing. Michaela Jurko; Valach, J.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2018, EPJ Web of Conferences - Volume 183 (2018) - DYMAT 2018 - 12th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, Les Ulis Cedex A, EDP Sciences - Web of Conferences), p. 1-6), ISBN 978-2-7598-9053-8, ISSN 2100-014X
Anotace:
In this paper, a split Hopkinson pressure bar (SHPB) was used for impact loading of an auxetic lattice (structure with negative Poisson’s ratio) at a given strain-rate. High strength aluminum and polymethyl methacrylate bars instrumented with foil strain-gauges were used for compression of an additively manufactured missing-rib auxetic lattice. All experiments were observed using a high-speed camera with frame-rate set to approx. 135.000 fps. High-speed images were synchronized with the strain-gauge records. Dynamic equilibrium in the specimen was analyzed and optimized pulse-shaping was introduced in the selected experiments. Longitudinal and lateral in-plane displacements and strains were evaluated using digital image correlation (DIC) technique. DIC results were compared with results obtained from strain-gauges and were found to be in good agreement. Using DIC, it was possible to analyze in-plane strain distribution in the specimens and to evaluate strain dependent Poisson’s ratio of the auxetic structure.
DOI:
10.1051/epjconf/201818302045
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Adorna, M.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Falta; Felten, M.; Fries, M.; Jung, A.
Publikováno:
2018, 16th Youth Symposium On Experimental Solid Mechanics, Praha, Česká technika - nakladatelství ČVUT, ČVUT v Praze), p. 72-76), ISBN 978-80-01-06474-0, ISSN 2336-5382
Anotace:
In this paper Split Hopkinson pressure bar (SHPB) was used for dynamic testing of nickel coated polyurethane hybrid foams. The foams were manufactured by electrodeposition of a nickel coating on the standard open-cell polyurethane foam. High strength aluminium alloy bars instrumented with foil strain-gauges were used for dynamic loading of the specimens. Experiments were observed using a high-speed camera with frame-rate set to approx. 100.000 – 150.000 fps. Precise synchronisation of the high-speed camera and the strain-gauge record was achieved using a through-beam photoelectric sensor. Dynamic equilibrium in the specimen was achieved in all measurements. Digital image correlation technique (DIC) was used to evaluate in-plane displacements and deformations of the samples. Specimens of two different dimensions were tested to investigate the collapse of the foam structure under high-speed loading at the specific strain-rate and strain.
DOI:
10.14311/APP.2018.18.0072
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 29-32), ISBN 978-80-01-06070-4, ISSN 2336-5382
Anotace:
The paper deals with investigation of deformation behaviour of gellan gum (GG) based structures prepared for regenerative medicine purposes. Investigated material was synthesized as porous spongy-like scaffold reinforced by bioactive glass (BAG) nano-particles in different concentrations. Deformation behavior was obtained employing custom designed experimental setup. This device equipped with bioreactor chamber allows to test the delivered samples under simulated physiological conditions with controlled flow and temperature. Cylindrical samples were subjected to uniaxial quasistatic loading in tension and compression. Material properties of plain GG scaffold and reinforced scaffold buffered by 50wt% and 70wt% BAG were derived from a set of tensile and compression tests. The results are represented in form of stress-strain curves calculated from the acquired force and displacement data.
DOI:
10.14311/APP.2017.7.0029
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Gantar, A; Novak, S
Publikováno:
2017, Acta Polytechnica, 57 (1), p. 14-21), ISSN 1210-2709
Anotace:
This study is focuses on an investigation of the reinforcement effect of the bioactive glass nano-particles in the gellan gum (GG) scaffolds used in bone tissue engineering. The investigated material was synthesized as the porous spongy-like structure improved by the bioactive glass (BAG) nano-particles. Cylindrical samples were subjected to a uniaxial quasi-static loading in tension and compression. Very soft nature of the material, which makes the sample susceptible to damage, required employment of a custom designed experimental device for the mechanical testing. Moreover, as the mechanical properties are significantly influenced by testing conditions the experiment was performed using dry samples and also using samples immersed in the simulated body fluid. Material properties of the pure GG scaffold and the GG-BAG reinforced scaffold were derived from a set of tensile and compression tests under dry and simulated physiological conditions. The results are represented in the form of stress-strain curves calculated from the acquired force and displacement data.
DOI:
10.14311/AP.2017.57.0014
Typ:
Článek v periodiku excerpovaném databází Scopus cizojaz.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Felten, M.; Fries, M.; Ing. Jan Falta; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Publikováno:
2017, 25th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY - PROGRAM AND BOOK OF ABSTRACTS, Ljubljana, Inštitut za kovinske materiale in tehnologije), ISBN 978-961-94088-1-0
Anotace:
In this paper, a Split Hopkinson Pressure Bar (SHPB) apparatus is used for impact loading of the selected cellular metallic materials. The experimental setup is arranged as a modified Kolsky setup. The experiment is observed using a high-speed camera for assessment of in-plane displacement and strain fields in the sample using digital image correlation (DIC). The functionality of the system is demonstrated on experiments where additively manufactured metallic auxetic lattices and nickel-coated open-cell polyurethane foam were used as specimens.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Publikováno:
2017, Advanced Engineering Materials, 19 (10), ISSN 1438-1656
Anotace:
In this paper, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatine. Samples from each group are tested under quasi-static loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasi-static and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05–1.4, whereas the effect of gelatine leads to increase of only 5–10%. Analysis of the Poisson's function reveals influence of filling on achievable (negative) values of Poisson's ratio, when compared to unfilled specimens. The results for the Poisson's function yielded apparently different values as the assessed minima of quasi-static Poisson's ratio in small deformations are constrained by a factor of 15.
DOI:
10.1002/adem.201700076
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Fíla, Ph.D.
Publikováno:
2017
Anotace:
In this study, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatin. Samples from each group are tested under quasi-static loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasi-static and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05–1.4, whereas the effect of gelatin leads to increase of only 5-10%. Analysis of the Poisson’s function reveals influence of filling on achievable (negative) values of Poisson’s ratio, when compared to unfilled specimens. The results for the Poisson’s function yielded apparently different values as the assessed minima of quasi-static Poisson’s ratio in small deformations are constrained by a factor of 15.
Typ:
Kandidátské minimum

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2017, 25th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY - PROGRAM AND BOOK OF ABSTRACTS, Ljubljana, Inštitut za kovinske materiale in tehnologije), p. 52-52), ISBN 978-961-94088-1-0
Anotace:
In this study behavior of selected types of filling material were tested in compressive loading mode at high strain rates. Four types of filling material were tested, (i) ordnance gelatin, (ii) low expan sion polyurethane foam, (iii) thixotropic polyurethane putty and (iv) silicon putty. To evaluate their contribution to the impact energy absorption in IPC bulk samples of selected materials were subjected to high strain rate compression. The high strain ra te compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was adjusted to be able to test cellular and soft materials. From the tests stress - strain diagrams of investigated materials were obtained, which provided relevant mechanical properties (plateau stress and strain, strain energy density).
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; doc. Ing. Petr Zlámal, Ph.D.; Kumpová, I.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Gantar, A.; Novak, S.
Publikováno:
2017, Materials and Technology, 51 (3), p. 397-402), ISSN 1580-2949
Anotace:
The presented work is aimed at a demonstration of modern radiological methods for an investigation of the deformation behaviour of bone scaffolds. Bone scaffold is an artificial structure used for the repairs of trabecular bones damaged by injuries or degenerative diseases. In bone-tissue engineering a proper description of its deformation behaviour is one of the most important characteristics for an assessment of the biocompatibility and bone-integration characteristics of the proposed structure intended to be used as a bone scaffold. According to recent studies bioactive-glass-reinforced gellan-gum (GG-BAG) is a promising material for bone-scaffold production. However, its low specific stiffness and simultaneous low attenuation to X-rays makes both the mechanical and imaging parts of the deformation experiments difficult. As a result a state-of-the-art experimental setup composed of high-precision micro-loading apparatus designed for the X-ray observation of deformation processes and an advanced radiographical device is required for such experiments. High-resolution time-lapse micro-focus X-ray computed tomography (micro CT) under loading in three different imaging modes was performed to obtain a precise structural and mechanical description of the observed deforming GG-BAG scaffolds.
DOI:
10.17222/mit.2015.237
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Adorna, M.; Fisher, C.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2017
Anotace:
Předložená práce se zabývá vyhodnocováním dynamických experimentů prováděných na instrumentovaném zařízení SHPB modifikovaném pro měření materiálů s nízkou mechanickou impedancí. V rámci práce je navržena a implementována metodika předzpracování zaznamenaných experimentálních dat, vytvořena sada softwarových nástrojů umožňující konzistentní a přesné vyhodnocení. Celé řešení je implementováno v modulárním uživatelském rozhraní, které umožňuje automatizované, rychlé a spolehlivé vyhodnocení zaznamenaných experimentálních dat. Navržené řešení je ověřeno v rámci vyhodnocení experimentů provedených na auxetické struktuře a na vzorku porézní polymerní pěny. Výsledky získané s použitím navrženého řešení jsou konzistentní a odpovídají již dříve publikovaným hodnotám. Výsledkem práce je soubor softwarových řešení implementovaný v uživatelském prostředí, který značně usnadňuje a zrychluje proces vyhodnocení experimentů provedených na SHPB.
Typ:
Diplomová práce

Autoři:
Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Publikováno:
2016, Materials and Technology, 50 (3), p. 311-317), ISSN 1580-2949
Anotace:
In the presented paper, three types of auxetic structures were produced with direct 3D printing and their compressive mechanical properties were tested. Samples were prepared from acrylic material suitable for high-resolution direct printing. Three different structures exhibiting in-plane and volumetric negative strain-dependent Poisson's ratio were selected for the analysis: two-dimensional missing-rib cut, two-dimensional inverted (re-entrant) honeycomb and three-dimensional inverted (re-entrant) honeycomb. The samples were subjected to quasi-static compression, from which stress-strain relationships were established. For a proper strain evaluation, digital-image correlation was applied to measure full-field displacements on the sample surfaces. From the displacement fields, true strain/true stress curves were derived for each sample. Furthermore, for each structure a three-dimensional FE model was developed using beam elements and subjected to identical loading conditions. Then, experimentally obtained stress-strain relationships were compared with numerically obtained results. For all the tested auxetic structures, the compressive behaviour was predicted well by the FE models. This demonstrates that parametric FE models can be used to tune the design parameters of the structures with a negative Poisson's ratio to optimize their overall properties.
DOI:
10.17222/mit.2014.204
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Hos, J.; Ing. Jan Šleichrt, Ph.D.
Publikováno:
2016, Materials and Technology, 50 (3), p. 413-417), ISSN 1580-2949
Anotace:
Composite materials with a polymeric matrix reinforced by carbon fibres are nowadays widely used as high-tech structural materials with excellent mechanical properties (particularly their stiffness and strength). The application of this type of composite to structural parts exposed to thermal loading has recently been proposed. Such an application requires an investigation and analysis of the mechanical behaviour under long-term exposure to simultaneous thermal and mechanical loading. In this paper the measurements and results of the creep behaviour of a composite with a polyphenylene sulphide matrix reinforced with chopped poly-acrylonitrile carbon fibres (C/PPS) are presented. The measured compound is proposed for use as a structural material for a jet-engine frame in the aerospace industry and the internal parts of aircraft with possible thermal loading. A custom experimental device designed for the creep measurements of composite materials was used for measurements of the developing strain at a constant tensile stress and temperature. Short-term creep tests with continuous strain monitoring were performed at a constant stress level at several elevated temperatures below and above the glass-transition temperature of the matrix. The strain was measured using the digital image correlation (DIC) method. The measured data were processed to find the strain-to-time dependency and the creep-compliance-to-time dependency. The creep-compliance-to-time data were also fitted using Findley's creep law for polymers to evaluate the model parameters and to analyse the applicability of the model for a PPS polymer reinforced with chopped carbon fibres.
DOI:
10.17222/mit.2014.208
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2016, Materials and Technology, 50 (3), p. 301-305), ISSN 1580-2949
Anotace:
The study aims at mechanical testing of an artificial bone structure in the form of a scaffold for the application in the repairs of trabecular bones after wounds or degenerative diseases. Such artificial construct has to conform to many requirements including biocompatibility, permeability properties and bone-integration characteristics. Recently, self-degradable bone scaffolds suitable for natural-bone-tissue ingrowth optimized with respect to mechanical properties and body-fluid flow have been considered as an alternative to allografts and autografts. Here, an analysis of deformation behaviour of a scaffold with a morphology identical to the natural bone is the first step in this task. In this work, the geometry and morphology of scaffold specimens produced with direct 3D printing were based on a 3D model derived from the X-ray-computed micro-tomography measurement of a real trabecular bone. The geometrical model was upscaled four times in order to achieve the optimum ratio between its resolution and the resolution of the 3D printer. For its biocompatibility and self-degradability, polylactic acid was used as the printing material. The mechanical characteristics were obtained from a series of uniaxial compression tests, with an optical evaluation of the strain field on the surfaces of the specimens. The acquired stress-strain curves were compared with the characteristics of a real trabecular bone obtained with time-lapse microtomography measurements, evaluated with the digital volumetric correlation method. The results show good correspondence of the stiffness values for both the natural and artificial bone specimens.
DOI:
10.17222/mit.2014.190
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Michaela Jurko; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2016, Engineering Mechanics 2015, Zurich, TRANS TECH PUBLICATIONS LTD), p. 428-434), ISSN 1662-7482
Anotace:
In this work parametric modelling was utilized to design and produce two types of porous microarchitectures with auxetic compressive properties suitable for deformation energy mitigation applications such as blast and bullet protection. The samples were directly produced from acrylic amaterial using a high resolution 3D printer and their compressive mechanical characteristics were tested. Two different structures exhibiting in-plane negative strain dependent Poisson’s ratio were selected for the analysis: i) two-dimensional inverted (re-entrant) honeycomb and ii) two-dimensional cut missing-rib. Stress-strain relationships were established from a set of quasi-static compressional experiments where the strain fields were evaluated using digital image correlation applied to measure the full-field displacements on the samples' surface. From the displacement fields true strain – true stress curves were derived for each sample and relative elastic moduli were evaluated.
DOI:
10.4028/www.scientific.net/AMM.821.428
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2016, Book of Abstracts of International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences 2016, Praha, katedra mechaniky a materiálů), ISBN 978-80-01-06009-4
Anotace:
This study is focused on investigation of the reinforcement effect of the nano-particles in gellan gum (GG) scaffolds used in bone tissue engineering. This hydrophilic polysaccharide-based material is attractive for personalized design of implants thanks to its biocompatibility and wide range of available fabrication methods. Material properties of pure GG scaffold and GG-BAG reinforced scaffold were derived from set of tensile and compression tests under dry and simulated physiological conditions. The results are represented in form of stress-strain curves calculated from acquired force and displacement data. It can be concluded that significant reinforcement effect of BAG was observed only during the compressive loading.
Typ:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Fíla, Ph.D.; Kumpová, I.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Vavřík, D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Publikováno:
2016, Journal of Instrumentation, 11 (1), ISSN 1748-0221
Anotace:
In this paper, we employ dual-energy X-ray microfocus tomography (DECT) measurement to develop high-resolution finite element (FE) models that can be used for the numerical assessment of the deformation behaviour of hybrid Ni/Al foam subjected to both quasi-static and dynamic compressive loading. Cubic samples of hybrid Ni/Al open-cell foam with an edge length of [15]mm were investigated by the DECT measurement. The material was prepared using AlSi7Mg0.3 aluminium foam with a mean pore size of [0.85]mm, coated with nanocrystalline nickel (crystallite size of approx. [50]nm) to form a surface layer with a theoretical thickness of [0.075]mm. CT imaging was carried out using state-of-the-art DSCT/DECT X-ray scanner developed at Centre of Excellence Telč. The device consists of a modular orthogonal assembly of two tube-detector imaging pairs, with an independent geometry setting and shared rotational stage mounted on a complex 16-axis CNC positioning system to enable unprecedented measurement variability for highly-detailed tomographical measurements. A sample of the metal foam was simultaneously irradiated using an XWT-240-SE reflection type X-ray tube and an XWT-160-TCHR transmission type X-ray tube. An enhanced dual-source sampling strategy was used for data acquisition. X-ray images were taken using XRD1622 large area GOS scintillator flat panel detectors with an active area of [410 × 410]mm and resolution [2048 × 2048]pixels. Tomographic scanning was performed in 1,200 projections with a 0.3 degree angular step to improve the accuracy of the generated models due to the very complex microstructure and high attenuation of the investigated material. Reconstructed data was processed using a dual-energy algorithm, and was used for the development of a 3D model and voxel model of the foam. The selected parameters of the models were compared with nominal parameters of the actual foam and showed good correlation.
DOI:
10.1088/1748-0221/11/01/C01005
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2016, Book of Abstracts of International Symposium on Experimental Methods and Numerical Simulation in Engineering Sciences 2016, Praha, katedra mechaniky a materiálů), ISBN 978-80-01-06009-4
Anotace:
This work presents deformation behaviour of cost effective chopped fiber composites. Use of chopped fibre is advantageous for manufacturing however complex shape parts production technology could be challenging. Batches of samples with different fibres composition were subjected to uni-axial tensile loading to obtain overall materials properties and inspection of proper manufacturing based on local deformation inhomogeneities. Deformation behaviour of chopped fibre composites represented by stress-strain curves and strain maps was described based on optical measurement of standard tensile test. Local strain concentrations predicting failure area was identified.
Typ:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A; Kumpova, I
Publikováno:
2016, Journal of Instrumentation, 11 (11), p. 1-7), ISSN 1748-0221
Anotace:
Hybrid foams are materials formed by a core from a standard open cell metal foam that is during the process of electrodeposition coated by a thin layer of different nanocrystalline metals. The material properties of the base metal foam are in this way modified resulting in higher plateau stress and, more importantly, by introduction of strain-rate dependence to its deformation response. In this paper, we used time-lapse X-ray micro-tomography for the mechanical characterization of Ni/Al hybrid foams (aluminium open cell foams with nickel coating layer). To fully understand the effects of the coating layer on the material’s effective properties, we compared the compressive response of the base uncoated foam to the response of the material with coating thickness of 50 and 75 µm. Digital volume correlation (DVC) was applied to obtain volumetric strain fields of the deforming micro-structure up to the densification region of the deforming cellular structure. The analysis was performed as a compressive mechanical test with simultaneous observation using X-ray radiography and tomography. A custom design experimental device was used for compression of the foam specimens in several deformation states directly in the X-ray setup. Planar X-ray images were taken during the loading phases and a X-ray tomography was performed at the end of each loading phase (up to engineering strain 22 %). The samples were irradiated using micro-focus reflection type X-ray tube and images were taken using a large area flat panel detector. Tomography reconstructions were used for an identification of a strain distribution in the foam using digital volumetric correlation. A comparison of the deformation response of the coated and the uncoated foam in uniaxial quasi-static compression is summarized in the paper.
DOI:
10.1088/1748-0221/11/11/C11017
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Keršner, Z.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2016
Anotace:
Pokročilé experimentální metody v mechanice vyžadují vývoj vlastních experimentálních zařízení, jejichž nezbytnou součástí je řídicí systém. V této práci je popsán návrh a realizace modulární řídicí jednotky poskytující otevřené řešení pro ovládání experimentálních zařízení. Navržená jednotka umožňuje ovládat zařízení s polohováním pracujícím na principu krokového motoru, popř. servo-motoru včetně bezpečnostních prvků, ovládat periferie a vyčítat veličiny měřené během experimentu (signál typu mV/V). V rámci práce byly rovněž vytvořeny softwarové nástroje pro implementaci řídicí jednotky do stávajících ovládacích aplikací pracujících na principu OS Linux s real-time jádrem a jeho speciálním modulem pro řízení LinuxCNC. V závěru byl proveden pilotní experiment s instrumentovaným mikroindentorem, který potvrdil funkčnost navrženého řídicího systému.
Typ:
Diplomová práce

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2016
Anotace:
Bylo vypracováno odborné posouzení konstrukce nového železničního návěstidla s využitím analytických výpočtů dle platných norem a numerických výpočtů metodou konečných prvků.
Typ:
Výzkumná zpráva v češtině

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Králík, V.
Publikováno:
2016, Engineering Mechanics 2015, Pfaffikon, Trans Tech Publications Inc.), p. 428-434), ISBN 978-3-03835-700-1, ISSN 1660-9336
Anotace:
Purpose of this study is investigation of energy absorption capability of the sandwich struc- tures composed of combination of polystyrene and metal foam element and their suitability as new structure for design of protective helmets. Two types of the metal foams were experimentally tested and evaluated: Alporas (Shinko Wire Ltd., Japan) and Aluhab (Aluinvent Plc., Hungary). Samples of the sandwich structure are composed of two layers: bottom expanded polystyrene (EPS 200S) layer and upper metal foam layer which are glued together. Prepared samples are tested using a drop tower experiment to measure sample response (acceleration, reaction force) at different strain rates and en- ergies. Acceleration/time history was used for the Head Injury Criterion (HIC) calculation. HIC is the significant parameter which expresses probability of head injury arising from an impact. Moreover, measured and derived characteristics are compared with pure EPS samples to obtain comparison of deformation behaviour between conventional structure for protective helmets and designed sandwich structures. Performed experimental work showed that Aluhab sandwich can be promising structure for protective helmet designs however further optimisation of the structure properties will be necessary.
DOI:
10.4028/www.scientific.net/AMM.821.420
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2015, Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 1-12), ISBN 978-1-905088-63-8, ISSN 1759-3433
Anotace:
This paper deals with finite element modelling of auxetic cellular structures and nu- merical optimization of their effective mechanical properties. Three different auxetic structures (two-dimensional cut missing-rib, two-dimensional inverted (re-entrant) hon- eycomb and three-dimensional inverted honeycomb) were designed and produced by additive manufacturing. Fully parametric representations of the structures are devel- oped based on their geometric design and tested in a virtual finite element experiment to uncover the relationship between the overall properties and design parameters. Deformation behaviour of the selected auxetics assessed numerically is verified against experiments in which deformation is measured precisely in a large area using digital image correlation up to large strain values. Then the strain-stress curves are compared to the numerically obtained values. In the finite element analyses the geometries of the structures have been discre- tised either with three-dimensional solid elements (eight-node hexahedral elements) and with beam elements. The numerical model was equipped with the elasto-plastic material model with a von Mises yield criteria and bilinear isotropic work hardening. To inversely calculate the stress-strain relationship of the structures for large strain values both geometric and material nonlinearities were taken into account. The effects of selected structural parameters (both geometric given e.g. by relative density, rod thickness, internal angles, etc. and material given by elastic properties of the base material) are studied using parametric finite element modelling to obtain their effects on overall mechanical properties (stiffness and strength). Auxetic structures are then optimized using design parameter driven finite element models which are able to predict various effective mechanical properties such as elastic modulus, strength and Poisson’s ratio.
DOI:
10.4203/ccp.108.153
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

Autoři:
Ing. Nela Krčmářová; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Šepitka, J.
Publikováno:
2015
Anotace:
Předložená práce se zabývá návrhem, výrobou a zprovozněním indentačního zařízení schopného indentace při nízkém zatížení metodou Vickers. Za tímto účelem byly navrženy dva způsoby zatěžování, první mód pro zatěžování konstantní silou při osazení indentoru závažím a druhý mód pro zatěžování řízené silou. Pro řízení indentačního zařízení technologií CNC byl vybrán modul LinuxCNC verze 2.6.4. Pro oba způsoby zatěžování vzniklo vlastní uživatelské rozhraní. Pro kontrolu správné funkce indentoru a vyhodnocovacích procedur bylo provedeno měření na referenční tvrdoměrné destičce. Toto měření dokázalo plnou funkčnost indentačního zařízení při nízkých zatěžovacích silách. Chyba měření byla mnohem menší, než chyba předepsaná normou.
Typ:
Diplomová práce

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2015
Anotace:
Nová koncepce nosné konstrukce světelného návěstidla byla předběžně posuzována z hlediska únosnosti pomocí FEM a analytického výpočtu podle normy, dále byla posuzována šroubová spojení a betonový základ.
Typ:
Výzkumná zpráva v češtině

Autoři:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2015, Materials and Technology, 49 (4), p. 597-600), ISSN 1580-2949
Anotace:
This paper deals with an experimental study of deformation response of open-cell aluminium foams under a moderate strain-rate compressive loading. Generally, porous metals show a promising potential in energy-absorption applications. However, the low strength of open-cell metal foams is a limiting parameter for such applications. Furthermore, the strain-rate sensitivity of mechanical properties is typically observed in closed-cell metal foams. On the other hand, open-cell foams provide a better control over the morphological parameters of a cellular structure. To enhance the properties of an open-cell microstructure an aluminium open-cell foam cured with polymeric filling was comparatively tested against the deformation-energy-absorption capabilities of the šas-delivered’ foam under a moderate strain-rate compressive loading. Prismatic samples with square cross-sections were prepared from the open-cell aluminium foam and a selected set of the samples was then filled with the thixotropic polyurethane putty. The specimens were tested with quasi-static compression, using a custom drop tower at several levels of the impact energy. The drop tests were instrumented with a tri-axial accelerometer and a high-speed camera to measure the mechanical response and the strain evolution during the impact. The comparison of the quasi-static behaviour with the results of the dynamic tests showed insignificant changes in the deformation curves in the case of the šas-delivered’ open-cell foam and an increasing energy-absorption capacity in the case of the samples equipped with the polymeric filling.
DOI:
10.17222/mit.2014.195
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Králík, V.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2015, Engineering mechanics 2015, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 420-427), ISBN 978-80-86246-42-0, ISSN 1805-8248
Anotace:
Purpose of this study is investigation of energy absorption capability of the sandwich structures composed of combination of polystyrene and metal foam element and their suitability as new structure for design of protective helmets. Two types of the metal foams were experimentally tested and evaluated: Alporas (Shinko Wire Ltd., Japan) and Aluhab (Aluinvent Plc., Hungary). Samples of the sandwich structure are composed of two layers: bottom expanded polystyrene (EPS 200S) layer and upper metal foam layer which are glued together. Prepared samples are tested using a drop tower experiment to measure sample response (acceleration, reaction force) at different strain rates and energies. From acceleration/time history the Head Injury Criterion (HIC) is calculated as significant parameters in terms of protective helmets. Moreover, measured and derived characteristics are compared with pure EPS samples to obtain comparison of deformation behaviour between conventional structure for protective helmets and designed sandwich structures.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Tomáš Mičunek, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Michal Frydrýn, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Drahomír Schmidt, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Zdeněk Svatý, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Luboš Nouzovský, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Lenková, A.; Ing. Petr Koudelka, Ph.D.; Ing. Bc. Kateřina Mičunková; Ing. Michaela Jurko; Hájková, B.; Ing. Jan Šleichrt, Ph.D.; Adorna, M.; Hos, J.; Ing. Jan Falta; Ing. Nela Krčmářová
Publikováno:
2015
Anotace:
Předmětem díla je porovnání neoriginálního náhradního dílu s originálním dílem kapoty Škoda Fabia II z pohledu bezpečnosti dopravy. Dále je předmětem díla zjištění zda neoriginální náhradní díly jednoho výrobce mají stejné mechanické vlastnosti.
Typ:
Výzkumná zpráva v češtině

Autoři:
Ing. Tomáš Fíla, Ph.D.; Kumpová, I.; Jandejsek, I.; Kloiber, M.; Tureček, D.; Vavřík, D.
Publikováno:
2015, JOURNAL OF INSTRUMENTATION, 2015 (10), ISSN 1748-0221
Anotace:
We present a novel dual-source/dual energy (DSCT/DECT) micro-tomography system including results of high-resolution DSCT reconstruction. The DSCT micro-tomography setup was designed as a multi-purpose X-ray imaging device equipped with two pairs of X-ray tubes and detectors in orthogonal arrangement with independent control of beam parameters. Both pairs (tube-detector) are mounted on a computer numerical control positioning system and can be independently set up to different geometries (e.g. with different magnification of each pair). In this work the simultaneous scanning of the object by two tube-detector pairs was used for approximately half reduction of tomography scanning time. The developed imaging procedure was applied for scanning of a wooden sample locally damaged during a semi-destructive test for assessment of wood quality. Prior to the tomography measurements the setup geometry was precisely adjusted in terms of magnification, horizontal and vertical tube-specimen-detector alignment of both pairs. DSCT measurements were carried out in sequence (2 x 90 degrees for each tube) with identical 100 mu m image resolution. It was proven that the presented experimental setup combined with appropriate control technique significantly reduces tomography scanning time of materials with complex micro-structure.
DOI:
10.1088/1748-0221/10/05/C05008
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Šperl, M.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 124-127), ISBN 978-80-01-05556-4
Anotace:
Carbon-fibre composite is very popular material in aircraft industry. Application of this material is limited by low fragility and low impact resistance. In flight airplane can be initialy damaged by hailstorm or bird strikes. The vibrations of the engine and turbulence during flight can be expansion of this damage. This study testing laser profilometry to investigation post damage under cycling loading.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šperl, M.
Publikováno:
2014, Materials and Technology, 48 (5), p. 777-780), ISSN 1580-2949
Anotace:
Carbon fibre in polyphenylene sulfide composites (C/PPS) became a popular material in the aircraft industry but its fragility and low impact resistance limits its application in primary aircraft structures. This study is focused on damage propagation in the laminated composites reinforced with carbon fibres. The damage may be inflicted during the ground maintenance, by an inflight bird strike or during a flight in severe meteorological conditions (heavy storms). The initial damage was created by a drop-weight out-of-plane impact using a spherical indenter. The response of the material was analysed by monitoring the impacted zones and their propagation history. The influenced area and specimen thickness in the centres of indents were chosen as the degradation parameters. The post-impact damage propagation induced by cyclic loading was assessed using a custom-designed computer-controlled laser-profilometery device. Both the upper and lower profiles of the specimen were scanned during the interruptions of the fatigue test. Global deformation was described with an analytically determined centroidal-axis curve. Local topography changes were obtained with a subtraction of this curve. Surface-deformation maps were created and used for a demonstration of the damage propagation in the specimen.
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Kumpová, I.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014, Book of abstract of 7th World Congress of Biomechanics, p. 597-597)
Anotace:
Micromechanical testing at the level of individual trabeculae is fundamental for proper description of deformation behaviour of a complex bone structure. This study is focused on influence of various X-ray microradiography procedures, loading procedures and tracking algorithms on accuracy of strain evaluation of loaded human trabeculae. Displacement controlled three-point bending test in both incremental and continual loading modes were carried out. To acquire best quality images two different X-ray imaging setups were used. Large area scintillator and high resolution single photon counting silicon detector WidePix with microfocus X-rays source were employed. Different voltages and target currents were tested to obtain optimal signal to noise ratio in the radiograms. Two different methods were used for displacement tracking: i) digital image correlation (DIC) and ii) tracking of artificial markers attached to the samples. In case of DIC sample inhomogeneity allowed for displacement measurement using Lucas-Kanade tracking algorithm. Gold coated borosilicate glass micro-spheres were used as the markers for displacement tracking in the second method. Here circular Hough transform was used to locate and track the positions of the markers in the loading sequence. Linearisation of the attenuation range was employed to improve contrast in the radiograms and to increase precision of the employed tracking algorithms. Stress-strain characteristics of individual trabeculae were obtained and reduction of thickness in loaded specimens correlating with strain localization was observed.
Typ:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Králík, V.; Němeček, J.; Jíra, A.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2014, 20 th International Conference Engineering Mechanics 2014, Brno, Brno University of Technology), p. 324-327), ISBN 978-80-214-4871-1, ISSN 1805-8248
Anotace:
Abstract: Aluminum foams are structural materials with excellent energy absorption capacity jointed with very low specific weight and high stiffness. Products of aluminum foams are used in a wide range of structural and functional applications (e.g. as a part of composite protection elements) due to its attractive properties. Full characterization of deformation behaviour under high-strain rate loading is required for designing these applications. The aim of this study is to compare stress-strain behaviour and energy absorption of the aluminium foam structure with conventional energy absorbing materials based on polystyrene and extruded polystyrene commonly used as protective elements. The compressive deformation behaviour of the materials was assessed under impact loading conditions using a drop tower experimental device.
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2014, 9th International Conference on Local Mechanical Properties, Zürich, Transtech Publications), p. 257-260), ISBN 978-3-03785-876-9, ISSN 1013-9826
Anotace:
The paper presents application on digital image correlation (DIC) and microindentation for investigation of plastic flow under Brinell ball indenter applied on steel specimen made of two screwed together parts. Specimens in two different material state (a) as delivered (b) annealed were investigated. This approach enables internal surface to act as the external one and to be examined by mentioned methods. Results obtained by application of DIC on scanning electron microscope (SEM) images are compared to microhardness maps and agreement is demonstrated.
DOI:
10.4028/www.scientific.net/KEM.586.257
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Králík, V.; Němeček, J.
Publikováno:
2014, Local Mechanical Properties X, Zurich, TRANS TECH PUBLICATIONS LTD), p. 39-42), ISBN 978-3-03835-062-0, ISSN 1013-9826
Anotace:
This study is focused on detection and characterisation of influenced zones in micro-scale specimens of aluminium foam after thermal and mechanical loading induced by preparation process for three-point bending test. Two cell-wall specimens were prepared from a slab of aluminium foam and influences of preparation process (machining) and thermal load on local mechanical properties were investigated using nanoindentation. Although the nanoindentation is powerful method for investigation of material properties of small zones, it can be reliably used only to obtain information about elastic properties. Due to limitation of the nanoindentation for reliable measurement of inelastic properties, plastic properties were determined using a set of indirect finite element simulations of nanoindentation tests. The procedure is based on fitting numerical results to experimentally measured force-depth curves.
DOI:
10.4028/www.scientific.net/KEM.606.39
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šepitka, J.; Lukeš, J.
Publikováno:
2014, Local Mechanical Properties X, Zurich, TRANS TECH PUBLICATIONS LTD), p. 245-248), ISBN 978-3-03835-062-0, ISSN 1013-9826
Anotace:
This study is focused on inspection of damage extent induced into C/PPS composite material by fatigue and impact loading. Initial damage to specimens was induced by drop-weight out-of-plane impact damage. Several levels of damage states (intact specimen, fatigued and impacted specimen, ruptured specimen) were inspected using modulus mapping (MM) technique. Quantification of the damage level was based on comparison of results from MM obtained in distinct locations on the specimens. Regions of interest were selected in order to determine magnitude of damage after impact and to assess remaining loading capabilities of the material. For this purpose, material maps provided information about location where matrix had been inflicted by the damage. Results show that impact loading has no measurable influence on mechanical properties of the matrix. However, gradient in mechanical properties was detected in the vicinity of crack. Results were validated using quasi-static nanoindentation and constant strain rate continuous measurement that showed depth profile of mechanical properties.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Králík, V.
Publikováno:
2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 145-150), ISBN 978-80-01-05556-4
Anotace:
The aim of this study is proper description of stress-strain behaviour of the metal foam structure Alporas under high-strain rate loading. Stress-strain response of Alporas specimens is measured during an impact test using a drop tower experiment. Strain of the specimens is evaluated by two independent approaches: i) double numerical integration of acceleration data and ii) digital image correlation technique. Thus, experimental setup is equipped with triaxial accelerometer and high speed camera. Resulting stress-strain curves are compared with behaviour of polystyrene material samples (polystyrene material is commonly used as a shock absorber) obtained from the same testing procedure and with stress-strain function determined from Alporas quasi-static compression testing.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014, XIVth Bilateral German/Czech Symposium - Experimental Methods and Numerical Simulation in Engineering Sciences, Wuppertal, Bergische Universität), p. 52-55)
Anotace:
The aim of this study is proper description of stress-strain behaviour of the metal foam structure Alporas under high-strain rate loading. Stress-strain curve of Alporas specimens is measured during an impact test using a drop tower device. Strain of the specimens is evaluated by two independent approaches: i) double numerical integration of acceleration data and ii) digital image correlation technique. Resulting stress-strain curves are compared with behaviour of polystyrene material samples and results obtained from quasi-static compression testing.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 61-65), ISBN 978-80-01-05556-4
Anotace:
Porous metals and particularly aluminium foams are attractive materials for crash applications where constructional elements have to be able to absorb considerable amount of deformation energy while having as low weight as possible. Compressive behaviour for medium impact velocities can be experimentally assessed from a series of drop-tower impact tests instrumented with accelerometer and high-speed camera. However to predict such behaviour a proper modelling scheme has to be developed. In this paper drop-tower impact tests of Alporas aluminium foam were used for development of a material model for explicit finite element simulations of high-strain rate deformation process using LS-DYNA simulation environment. From the material models available low density foam, Fu-Chang’s foam, crushable foam and modified crushable foam models were selected for simulations using smoothed-particle hydrodynamics and solid formulations respectively. Numerical simulations were performed in order to assess constitutive parameters of these models and identify material model describing deformation behaviour of Alporas with the best accuracy.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Fíla, Ph.D.; Kumpová, I.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 32-35), ISBN 978-80-01-05556-4
Anotace:
In this paper, compact loading device for micro-CT measurements under applied load was used in a series of instrumented compressive test of bone sample. Tested bone samples were loaded in several deformation steps and micro-CT scanning was carried out in each step. Reconstructed three-dimensional data of intact bone sample were used to develop 3D model of the specimen. Data from each deformation step were processed by DVC method for identification of displacement and strain fields and thus for evaluation of deformation response of human trabecular bone sample.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Kumpová, I.
Publikováno:
2014, XIVth Bilateral German/Czech Symposium - Experimental Methods and Numerical Simulation in Engineering Sciences, Wuppertal, Bergische Universität), p. 66-69)
Anotace:
Deeper understanding of the relationship between morphology, micro-mechanical properties at the bone tissue level and overall mechanical properties of the bone is important for assessment of bone physiological and pathological behaviour. Modern radiological methods (e.g. computed micro-tomography) are powerful instruments for investigation of the internal structure. Using the time-lapse tomography enabled assessment of deformation response to the applied loading and monitoring of damage propagation. Different custom based set-ups of high resolution micro-focus X-ray computed tomography equipped with scintillator or single-photon counting detector were used for imaging at both meso and micro levels.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Publikováno:
2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)
Anotace:
Evaluation of natural frequencies‘ shift during thermal loading of carbon fibre/polyphenylene sulphide (C/PPS) composites used in aircraft industry is described in this paper. Values of natural frequencies were chosen as indicators of changes in material properties. Custom-designed experimental device suitable for determination of specimen's natural frequencies was developed according to operation in thermal chamber. During the experiment steel pellets were dropped on specimen. Overall acoustic response of the impact was recorded by microphone. Two characteristic natural frequencies were evaluated using spectral analysis of recorded sound. Series of measurements at different temperatures were performed nearly up to the temperature of PPS glass-transition. Obtained results show strong correlation between natural frequency shift and temperature of the specimen’s surface.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šperl, M.
Publikováno:
2013, UPB Scientific Bulletin, Series D: Mechanical Engineering, 75 (2), p. 157-164), ISSN 1454-2358
Anotace:
Carbon fibre in polyphenylene sulfide composites became popular ma- terial in aircraft industry but its fragility and low resistance against impact load- ing limits the application of these composites in aircraft primary structures. The article deals with experimental investigation of the mechanical response of dam- aged composite. Material degradation of intact and damaged specimens during fatigue tests was investigated. The changes in natural frequencies, ultrasound wave propagation and bending stiffness were chosen as damage parameters. The entire fatigue life of intact and damaged specimens was studied in the article by all the presented methods. The accuracy and reliability of assessment of damage parameters were compared. Comparison of accuracy and reliability of presented method for assessment of damage parameters is also given.
Typ:
Článek v periodiku excerpovaném databází Scopus

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)
Anotace:
This paper is focused on evaluation of the micro‐scale tests of isolated cell‐walls of aluminium foam. To derive mechanical properties at the level of single cells, three point bending tests were carried out. There are several ways to obtain mechanical properties from the measured data (i) manufacturing of prismatic beam, (ii) testing of a curved beam and simplification of the beam shape by an equation of a curve, (iii) indirect determination of mechanical properties using inverse finite element analysis (FEA). Due to the dimensions and complex shape of the cells there is a high risk of plastic deformation caused by specimen preparation as well as very low dimensions of resulting sample. Hence testing of a curved specimen was performed with a special attention paid to the specimen preparation. A volumetric model enabling utilization of inverse FEA was developed.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Žďárský, M.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Šperl, M.; Ing. Tomáš Fíla, Ph.D.
Publikováno:
2013, Proceedings of 12th International Workshop on Advanced Infrared Technology and Applications, Politecnico di Torino), p. 217-219)
Anotace:
The presented work summarizes first results on hi-speed thermography analysis of cyclic loading of carbon fibers reinforced thermoplastic matrix composite. Opportunity to record and analyze minute changes of temperature is shown as well as detailed documentation of energy dumping on gradual increase of mean temperature of the specimen. Demonstrated sensitivity of the thermoanalysis is prerequisite for future investigation of impact damage as discussed in conclusions.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2013, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-57-7, ISSN 1759-3433
Anotace:
This paper describes the determination of the elasto-plastic properties of base material of aluminium foam Alporas. Three point bending experiments at the micro-scale level in conjunction with inverse finite element simulation were performed. In the cellular structure cell-walls with planar shape were identified and vicinity of such walls was extracted. Harvestedmaterial was embedded into transparent rosin to avoid plastic deformation during the manipulation and the selected wall was extracted. The specimens were finalized by grinding and polishing to achieve approximately rectangular shape. Three projections were acquired using a scanning electron microscope (SEM) and a volumetric model of the samples was developed using a semiautomatic image processing tool. Amicro-scale three-point bending test of semi-prismatic specimens extracted from the cell-wall was performed using a custom designed loading device. Loading was provided using a preloaded lead screw with precise travel. Applied force was measured using a high-accuracy load cell with a loading capacity of 2.25N. Strains were measured optically using the digital image correlation method. The volumetric model developed from the set of SEM projections was discretised using tetrahedral elements with quadratic shape functions. In the simulated bending test the elasto-plastic material model with the von Misses yield criterion and bilinear isotropic hardening was used. Boundary conditions consistent with the experimental oneswere prescribed in the simulation. Themeasured force was sampled at 50Hz and applied to the finite elementmodel. Based on themeasured displacements, parameters of the material model were varied to obtain a best fit to the experimental data (load- deflection curve). Elastic and plasticmaterial constants of the constitutivemodel were identified: (i) Young’smodulus of elasticity, (ii) yield stress and (iii) tangentmodulus.
DOI:
10.4203/ccp.102.104
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; Jandejsek, I.; Vavřík, D.
Publikováno:
2013, Journal of Instrumentation, 8 (2), ISSN 1748-0221
Anotace:
Time-lapse X-ray computed microtomography was employed to quantify the deformation behaviour of closed-cell aluminium foam. The specimen was incrementally loaded and tomographically scanned using a custom X-ray tomographic device to capture the deforming microstructure. Because of the very small thickness of the cell walls and the high ratio between pore size and cell wall thickness cone-beam reconstruction procedure was applied. A finite element (FE) model was developed based on the reconstructed three-dimensional data. The FE model was used for two purposes: i) the nodal points were used for tracking the displacements of the deforming structure, ii) verification of the material model for description of the foam's deformational behaviour. Digital volumetric correlation (DVC) algorithm was used on data obtained from the time-lapse tomography to provide a detailed description of the evolution of deformation in the complex structure of aluminium foam. The results from DVC demonstrate the possibility to use the complex microstructure of the aluminium foam as a random pattern for the correlation algorithm. The underlying FE model enables easy comparison between experimental results and results obtained from numerical simulations used for evaluation of proposed constitutive models.
DOI:
10.1088/1748-0221/8/02/C02012
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Minster, J.; Kostelecká, M.
Publikováno:
2012, Chemické listy, 106 (s3), p. 399-400), ISSN 0009-2770
Anotace:
The article deals with monitoring of degradation of carbon fibre reinforced polymer (CFRP) under cyclic loading. The investigated material is composed of polyphenylensulfid matrix and carbon fibres. Four specimens were subjected to repeated cyclic loading. During the fatigue loading surface of tested specimens was observed by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) to obtain surface roughness characteristics and micrographs of surface morphology. With increasing number of cycles the measured surface characteristics showed increasing surface roughness indicating at the level of micromechanics detachment of matrix from the fibers and also changes in the matrix structure itself.
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Fíla, Ph.D.; Urushadze, S.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šperl, M.
Publikováno:
2012, Engineering Mechanics 2012, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 231-237), ISBN 978-80-86246-39-0
Anotace:
Assessment of degradation rate of material can be carried out by many experimental techniques differing in complexity and sophistication. A relatively simple method based on acoustic analysis is described in this contribution. Degradation of material's properties due to fatigue loading is detectable in decrease of their modulus of elasticity that can be derived from natural frequencies of specimens, which were acquired by the presented method. These measurements utilize self-designed device capable of specimen excitation and acquisition of its vibration. The recorded signal is then processed by spectral analysis enabling determination of natural frequencies. Usefulness of the above mentioned acoustic method can be seen in the fact that the measured changes of material's parameters are comparable to those obtained by laser vibrometry, which is by several orders more expensive technique.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Minster, J.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2012
Anotace:
Tato práce se zabývá nedestruktivním testováním uhlíkového kompozitu s polymerní matricí C/PPS. Za tímto účelem byla zvolena metoda určování degradace materiálu pomocí akustických charakteristik. Tato metoda byla významně upravena, bylo zkonstruováno vlastní experimentální zařízení a vyvinut vlastní software pro měření a vyhodnocování dat. Pomocí těchto nástrojů byly evaluovány vlastní frekvence vzorku a jejich logaritmický dekrement útlumu. Měřené změny těchto veličin byly následně použity jako indikátory poškození materiálu únavovou degradací.
Typ:
Diplomová práce

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Publikováno:
2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 92-95), ISBN 978-1-63439-432-1
Anotace:
Abstract: This paper deals with investigation of acoustic material degradation indicator (natural frequency) of carbon fibre C/PPS composite obtained by a custom-built experimental device. The specimen's sound was emitted during the impact of steel pellet in acoustic measurement experimental device. Acoustic signals were recorded and analyzed using spectral and regression analysis. Specimens were repetitively measured after designated number of loading cycles. The decreases of natural frequencies were determined for given number of natural modes. Relations between natural frequency values and their decreases were investigated. To conclude, the data assessed using acoustic measurements are suitable for evaluation of material degradation.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; Urushadze, S.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Šperl, M.
Publikováno:
2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 35-38), ISBN 978-80-01-05062-0
Anotace:
This paper deals with investigation of acoustic material degradation indicator (attenuation decrement drop of selected natural frequency) measured by a custom-built experimental device. Samples of C/PPS fibre composite material were analyzed. Acoustic signals were recorded and processed using spectral analysis and sound signal regression. Data measured by this method were verified by comparative experiment. Specimens were simultaneously measured using both acoustic experimental device and laser vibrometer. Modal analysis of the specimen were carried out prior to the experiment. This enabled assessment of specimens natural modes and therefore the best impact zone. In total, 10 measurements were performed for each specimen at the same level of degradation. Measured data were then processed and compared. The specimens were repetitively measured after designated number of loading cycles. To conclude, the data assessed using acoustic measurements are comparable in terms of precision, reproducibility and reliability with results from laser vibrometer and the method is suitable for evaluation of material degradation.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 263-266), ISBN 978-1-63439-432-1
Anotace:
From a mechanical point of view the most important ability of metal foam is absorption of large amounts of strain energy. This advantage is based on the cellular structure with high ratio of porosity (75-95%). The aim of this study is determination of stress-strain measurement protocol for closed-cell aluminium metal foam Alporas during a compression test using in-house loading device. Changes in structure were observed and strain was calculated based on Digital Image Correlation (DIC) technique. For the assessment of overall compression elastic modulus a new software tool based on the Matlab toolkit was developed.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Fíla, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Šperl, M.
Publikováno:
2011, Experimentální analýza napětí 2011, Brno, Brno University of Technology), p. 49-55), ISBN 978-80-214-4275-7
Anotace:
The article deals with assessment of fatigue degradation of C/PPS composites using simple acoustic measurement technique. Changes in natural frequency and attenuation decrement were chosen as indicators of fatigue damage accumulation in the studied composite material. New testing device was developed for acoustic measurement. The experimental setup was designed to chime the specimen by repeatable force of stiff striker exciting a specific natural mode of vibration and to record the acoustic response of the specimen to the impact simultaneously. From the power spectral density of the signal the natural frequency was obtained. Using the same signal, the attenuation decrement was estimated from regression of the its envelope. Presented high precision non-destructive method allows to conclusively measure the natural frequency and its change with a deviation smaller than a few tenths per cents.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně