Lidé na fakultě
doc. Ing. Petr Zlámal, Ph.D.

rozklikni NABÍDKU

Publikace

informace pocházejí z univerzitní databáze V3S

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

Autoři:
Ing. Lukáš Zeman; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Nela Krčmářová; Koudelková, V.; Zeman, J.
Publikováno:
2023, Young Transportation Engineers Conference 2022, Praha, České vysoké učení technické v Praze), p. 89-97), ISBN 978-80-01-07224-0, ISSN 2336-5382
Anotace:
The article presents a study of the mechanical processes occurring during the aluminothermic reaction using experimental methods (strain gauges, digital image correlation, thermography, scanning electron microscopy, profilometry). The aluminothermic reaction is a highly efficient welding method due to its exothermic behaviour, however, it places considerable demands not only on the welding technique, but also on the capabilities of the experimental methods used; these limitations are also discussed in the article. The aluminothermic reaction is associated with the formation of a localised heat source with a time evolution dictated by the technological procedure, which manifests itself in heat propagation to the surrounding weld material. The unequal evolution of the temperature field is the fundamental cause of the appearance of the heat affected zone or local deformations or surface curvature, which was the focus of the experimental methods deployed above and the results of which are shown in the article.
DOI:
10.14311/APP.2023.41.0089
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

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

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

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

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

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

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

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

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

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

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

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

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

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

Autoři:
Ing. et Ing. Radim Dvořák; Ing. Petr Koudelka, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2018
Anotace:
Předmětem této bakalářské práce je shrnutí poznatků a faktů o šíření vlnění jednorozměrným kontinuem, zejména v dlouhých tenkých tyčích, o principech měření metodou SHPB, o technikách tvarování pulzu a okrajově i o metodách numerické mechaniky. Z teoretického úvodu vychází část praktická, kde je vytvořen zdrojový kód pro tvorbu parametrického modelu typické sestavy SHPB pro prostředí LS-DYNA. Redukovaná sestava je pak metodou konečných prvků podrobena citlivostní studii. Nakonec je provedena parametrická studie tvarovače pulzu, která sleduje vliv geometrických vlastností tvarovače na tvar napěťového pulzu a která je včetně s procesů s ní spjatých algoritmizována, čímž je umožněno snadné zpracování výsledků a případné srovnání s experimentálními daty. Primárním výstupem práce jsou výsledky parametrické studie v podobě kvantifikované míry vlivu geometrie tvarovače na změnu tvaru pulzu a automatizační algoritmy pro tvorbu modelů, provedení simulací a vyhodnocení výsledků.
Typ:
Diplomová práce

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

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

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

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

Autoři:
Ing. Jan Falta; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Šperl, M.
Publikováno:
2017
Anotace:
Tato práce řeší problematiku instrumentace dělené Hopkinsonovy tyče modifikované pro dynamická měření materiálů s nízkou mechanickou impedancí. Zaměřuje se na návrh a realizaci součástí souvisejících se samotným záznamem deformačních pulzů z tenzometrických snímačů (jednotka pro tenzometrická měření, napájecí jednotka, filtrace) až po součásti sloužící k řízení a synchronizaci experimentu (modul optických bran a trigger vysokorychlostní kamery). Součástí práce je také návrh softwarového řešení, s grafickým uživatelským rozhraním, umožňujícím nastavení parametrů záznamu měření, samotné zaznamenání měřených veličin a jejich uložení pro potřeby vyhodnocení experimentu. Použitelnost a spolehlivost implementovaného řešení pro rutinní experimenty instrumentovaného SHPB je potvrzena provedenými experimenty se vzorky auxetických struktur. Tyto experimenty se následně podařilo spolehlivě vyhodnotit. Výsledkem této práce je soubor technických řešení (hardwarových i softwarových) zlepšujících kvalitu a spolehlivost měřených dat a také zvyšující celkový komfort obsluhy instrumentovaného zařízení SHPB.
Typ:
Diplomová práce

Autoři:
Ing. Tomáš 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:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2016, ISBN 978-80-01-06009-4
Typ:
Sborník z mezinárodní konf. v češtině

Autoři:
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. 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:
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:
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:
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:
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:
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:
doc. Ing. Petr Zlámal, Ph.D.; Gutermann, M.; Minster, J.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014
Anotace:
The aim of the study is to develop and validate experimental and numerical modelling techniques for the investigation of deformation behaviour of a porous material. For this purpose, a trabecular bone as biological porous material was chosen. Development of the mictrostructural model with a complex inner structure consisted of three main parts: i) identification of the material model; ii) a precise description of the inner structure; iii) validation of the resulting microstructural model. Identification of the material model was based on micro (three-point bending) and nano-mechanical (nanoindentation) testing of the single trabeculae (single trabecula is the basic building element of trabecular tissue). These tests were simulated using the finite element method and the calculated results were compared (using the least square method) to experimental obtained values. In this way the best set of the material constants for elasto-visco-plastic model with damage for single trabecula were identified. To obtain a geometrically accurate finite element model of the trabecular microstructure and suitable experimental data for model validation the time-lapse micro-computed tomography scanning of compression test was performed. The sample was placed into a loading device and subjected to incremental compressive loading and each deformation step was observed using X-ray microradiographic imaging. Radiographic data were reconstructed and a high resolution voxel model was prepared from the tomography of the undeformed state. The identified material model from nano and micro-mechanical testing was prescribed to the voxel model and the simulation of the compression test was performed to verify its reliability to predict the deformation behaviour of bone. The calculated deformation fields were compared with the corresponding deformation fields which were determined from tomographically captured load states using the digital volume correlation method.
Typ:
Disertační práce (PhD)

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

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

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Růžička, M.
Publikováno:
2014, ISBN 978-80-01-05556-4
Typ:
Sborník z mezinár. konf. cizojazyčně

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

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jandejsek, I.
Publikováno:
2014, 9th International Conference on Local Mechanical Properties, Zürich, Transtech Publications), p. 265-269), ISBN 978-3-03785-876-9, ISSN 1013-9826
Anotace:
The aim of this study is to determine constitutive constants for elasto-plastic material model with damage for single trabecula based on the indirect simulation of micromechanical testing and its verification at macro level using compression test of the cylindrical sample of the trabecular tissue. Three-point bending test of isolated trabeculae was performed in a shielding box and deflection of the sample was acquired using X-ray microradiography. Measured values (displacements of markers) were used for indirect identification of the material model for single trabecula using finite element (FE) method. The bending test was simulated and results were fitted to experimentally obtained values and the appropriate set of material constants was determined. To verify the applicability of the identified material model the compression test of the complex sample was carried out. Cylindrical sample was incrementally loaded and each loading state was captured using the micro-computed tomography. Material model identified from three-point bending test was applied to the model of complex sample and the simulation of the compression test was performed.
DOI:
10.4028/www.scientific.net/KEM.586.265
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Publikováno:
2013, Acta Technica CSAV, 58 (2), p. 157-171), ISSN 0001-7043
Anotace:
The aim of the paper is to develop a procedure for determination of elasto-visco-plastic constitutive model with damage for human single trabecula. The procedure is suited for indirect establishing of material model based on nanoindentation and three-point bending test. Constants of the material model are identified by Finite Element (FE) simulations and curve fitting using an algorithm based on least squares fitting of the experimental curves. In the case of nanoindentation, the penetration depth of tip during the FE analyses (FEA) is fitted to experimental nanoindentation curves. In the case of three-point bending, displacements of nodes are compared with displacements of markers observed during the experiment using digital image correlation.
Typ:
Článek v periodiku excerpovaném databází Scopus cizojaz.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Jandejsek, I.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Drahomír Schmidt, Ph.D.
Publikováno:
2013, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-57-7, ISSN 1759-3433
Anotace:
The possibility of using microstructural finite element models of whole bones to inversely calculate their mechanical properties is described in this paper. In this study, L2 vertebra of a Wistar rat were used to numerically determine its stiffness and the results are compared with the experimentally obtained value. The results demonstrate the possibility of using these large-scale finite element simulations to predict the overall bone stiffness. The micro-structural models used in this study are voxel-based, i.e. each finite element represents one spatial pixel (called a voxel). The micro-structural models are developed from a series of micro-CT images. The resolution of the input image data which is needed to capture the complex microstructure of trabecular bone in sufficient detail is discussed. Tissue material properties are based on our previous nanoindentation study. This paper is focused on the parallel solution strategy employed to solve the large-scale finite element models utilizing existing open-source programs. Because of the high resolution of the microtomographic images the resulting finite element model of the vertebra is composed of approximately 9 million of hexahedral elements. To solve this large problem a parallel strategy must be employed. The main aim was to demonstrate the scalability of selected solvers (the preconditioned conjugate gradient and multifrontal massively parallel sparse direct solver) for these large voxel finite element models. Two architectures are tested: i) distributed memory system, and ii) shared memory system. The results show, that the estimated overall stiffness of the vertebral body is not greatly influenced by the resolution of micro-CT images (albeit it must well capture the micro-structural characteristics of the trabecular bone) provided that the tissue material properties (elastic modulus and Poissons ratio at the level of individual trabeculae) are known.
DOI:
10.4203/ccp.102.105
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Jandejsek, I.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Drahomír Schmidt, Ph.D.
Publikováno:
2013, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-57-7, ISSN 1759-3433
Anotace:
The possibility of using microstructural finite element models of whole bones to in- versely calculate their mechanical properties is described in this paper. In this study, L2 vertebra of a Wistar rat were used to numerically determine its stiffness and the results are compared with the experimentally obtained value. The results demonstrate the possibility of using these large-scale finite element simulations to predict the over- all bone stiffness. The micro-structural models used in this study are voxel-based, i.e. each finite element represents one spatial pixel (called a voxel). The micro-structural models are developed from a series of micro-CT images. The resolution of the input image data which is needed to capture the complex microstructure of trabecular bone in sufficient detail is discussed. Tissue material properties are based on our previous nanoindentation study. This paper is focused on the parallel solution strategy employed to solve the large-scale fi- nite element models utilizing existing open-source programs. Because of the high res- olution of the microtomographic images (≈5µm3) the resulting finite element model of the vertebra is composed of approximately 9 million of hexahedral elements. To solve this large problem a parallel strategy must be employed. The main aim was to demonstrate the scalability of selected solvers (the preconditioned conjugate gradient and multifrontal massively parallel sparse direct solver) for these large voxel finite element models. Two architectures are tested: i) distributed memory system, and ii) shared memory system. The results show, that the estimated overall stiffness of the vertebral body is not greatly influenced by the resolution of micro-CT images (albeit it must well capture the micro-structural characteristics of the trabecular bone) provided that the tissue material properties (elastic modulus and Poisson’s ratio at the level of individual tra- beculae) are known.
DOI:
10.4203/ccp.102.105
Typ:
Stať 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.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 88-91), ISBN 978-1-63439-432-1
Anotace:
This paper deals with development of the volume model of irregular specimens using optical projections. A s equence of 360 projections of the specimen was acquired and processed using a custom set of procedures developed in MatLab environment. The projections were segmented, filtered and smoothed. A semiautomatic procedure was used to calibrate scale of the projections and to remove eccentricity of axis of rotation of the specimen. The volume model was obtained using inverse Radon transform. Additional procedures were developed to o btain cross- section characteristics required for e valuation of corresponding micromechanical test. For verification of the developed procedure volume models of known shaped objects were estimated and compared.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Králík, V.
Publikováno:
2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 107-110), ISBN 978-80-01-05062-0
Anotace:
The aim of this study is to determine elasto-visco-plastic material model with damage for two basic structure elements of diferent porous materials: (i) human single trabecula and (ii) wall of Alporas metal foam. Indirect identification of constants of the material model is based on the numerical simulations of the nanoindentation test using custom-built optimization algorithm. During the optimization procedure the numerical results are fitted to the experimentally obtained nanoindentation curves and the best set of the constants is determined using the least squares method. For evaluation of the influence of the individual material constants a sensitivity study is performed.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Publikováno:
2012, Engineering Mechanics 2012, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 1611-1620), ISBN 978-80-86246-40-6
Anotace:
The aim of the paper is to develop a procedure for determination of elasto-visco-plastic constitutive model with damage for human single trabecula. The procedure is suited for indirect establishing of material model based on nanoindentation and three-point bending test. Constants of the material model are identified by Finite Element (FE) simulations and curve fitting using an algorithm based on least squares fitting of the experimental curves. In the case of nanoindentation, the penetration depth of tip during the FE analyses (FEA) is fitted to experimental nanoindentation curves. In the case of three-point bending, displacements of nodes are compared with displacements of markers observed during the experiment using digital image correlation.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
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:
doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2012, Journal of Biomechanics, 45 (S1), p. 479-479), ISSN 0021-9290
Anotace:
The single trabecula is basic beam-shaped element of bone structure. To improve knowledge of deformation behaviour of cancellous bone a mechanical tests at the level of single trabecula were performed. Elasto-plastic material properties (Young's modulus and yield point) of single trabecula, assumed as an isotropic material, were assessed from three-point bending tests. Three-point bending test was simulated using Finite Element (FE) analyses and results were compared with experimental ones for determination of suitable material model for single trabecula.
DOI:
10.1016/S0021-9290(12)70480-3
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2012, Chemické listy, 106 (S3), p. 572-573), ISSN 0009-2770
Anotace:
In this study a novel micromechanical device has been developed. Precision of the setup has been evaluated using specimens of known material properties. Applied force was measured with capacity load sensor and the strains were measured optically. Samples of trabeculae were harvested from human proximal femur. A FE model of trabecula was developed and three-point bending test was simulated. From displacements of markers, strain values were computed. Resulting displacements of markers from FEA were fitted to experimentally obtained ones and set of parameters of the material model was determined.
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šepitka, J.; Lukeš, J.
Publikováno:
2012, Chemické listy, 106 (s3), p. 442-445), ISSN 0009-2770
Anotace:
This study aims to investigate the local variations in material properties of single human trabecula in its cross-section. Thin and straight trabeculae were located in a thin slice of trabecular bone extracted from proximal femur. Tensile and three-point bending tests were performed to determine elastic modulae, yield strains and yield stresses. To determine local variations in elastic properties in trabecula's cross-section, modulus mapping (MM) technique was applied in samples' undamaged parts. Using MM the storage and loss modulae are determined. Correlation between average elastic properties in cross-section and properties from micromechanical tests was found for all tested samples.
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.
Publikováno:
2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 127-128), ISBN 978-1-63439-434-5
Anotace:
Knowledge of trabecular bone behaviour under loading is very important for the bone quality assessment. For investigation of deformation behaviour of trabecular bone a combination of computational and experimental method was used. In this study suitable visco-elasto/plastic material model for single trabeculae was established from numerical simulation of nanoindentation test. The visco-elasto/plastic model with von Mises yield criterion and bilinear isotropic hardening with implicit creep was chosen. Pure elastic material constants can be determined directly from nanoindentation test by Oliver-Pharr method. Other constants determining the plastic and creep behaviour of the model have to be identified indirectly by fitting the load-displacement curve to results from the Finite Element (FE) simulation of nanoindentation test. For statistically significant fitting procedure a multiple indents (10um grid size) with different loading rates, holding times and peak loads were performed.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, J.; doc. Ing. Petr Zlámal, Ph.D.; Kostelecká, M.
Publikováno:
2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 71-72), ISBN 978-1-63439-434-5
Anotace:
Article deals with describing of the pre-testing procedure for the uniaxial testing, nanoindentation and finite element modeling of single trabeculae. The first part is focused on the specimen resection, delipidation and fixation in a novel high precision experimental device which enables to measure the strains optically using a high-resolution CCD camera. The second part deals with the development of the volumetric model of the trabecula required for numerical analysis. The last part is dedicated to optimization of polishing procedure used sample surface preparation for nanoindentation. Effect of the grain size, load and duration time of the grinding on final surface roughness was analyzed. Change in the surface roughness was monitored during the preparation process using a confocal microscope. Optimized procedure of sample preparation for micro-mechanical testing with satisfactory results is presented in the paper.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.; doc. Ing. Petr Zlámal, Ph.D.; Pokorný, D.
Publikováno:
2011, Frattura ed Integrita Strutturale, 5 (15), p. 5-13), ISSN 1971-8993
Anotace:
The quality of bonding between the acetabular cup and pelvis bone plays a key role in total hip replacement stability. One of the source of potential loss of the primary stability is the cement layer degradation. The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of the sample of pelvic bone with implanted cemented acetabular component. The process of damage accumulation in cement fixation was monitored by repeated scanning using high resolution micro Computed Tomography. Use of microfocus source and large high resolution flat panel detector allows investigation of structural changes as well as development of full-scale micro-structural models.
DOI:
10.3221/IGF-ESIS.15.01
Typ:
Článek v odborném recenzovaném periodiku

Autoři:
Jiroušek, O.; Němeček, J.; doc. Ing. Daniel Kytýř, Ph.D.; Kunecký, J.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Publikováno:
2011, Chemické listy, 105 (17), p. 668-671), ISSN 0009-2770
Anotace:
The published mechanical properties of human trabecular bone vary between 1GPa and 15GPa. The cause of this broad discrepancy in results might be in sample preparation, different testing protocols or anisotropy and asymmetry of the micro-samples. The article deals with a comparison between the properties assessed using nanoindentation and properties measured using uniaxial testing of single trabeculae. A novel experimental device was developed for high precision loading control. The strains at the surface of the sample are measured using a high-resolution CCD camera. The strain field is evaluated by precise DIC algorithm applied to whole surface of the loaded sample. The mechanical properties measured on micrometer-sized specimens using both methods (nanoindentation and micro-mechanical testing) are prescribed to FE model. The sample is then loaded according to the experimental procedure. The response of the FE model (stress-strain curve) is compared to results from the tensile test.
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Jandejsek, I.
Publikováno:
2011, Journal of Instrumentation, 6 (11), p. 1-6), ISSN 1748-0221
Anotace:
X-ray microradiography was used to quantify the strains in loaded human trabecula. Samples of isolated trabeculae from human proximal femur were extracted and glued in a loading machine specially designed for testing of small specimens. The samples were tested in tension and three-point bending until complete fracture occured. Real-time microradiography in conjunction with digital image correlation has been used. The samples were irradiated continuously by X-rays. Radiographs were acquired using 0.25s exposure time with hybrid single-photon counting silicon pixel detector Medipix2. Designed loading device enables for precise control of the applied displacement which is important for the post-yield behavior assessment. Tested experimental setup enables to combine micromechanical testing of the basic building block of trabecular bone with time-lapse X-ray radiography to assess the mechanical properties of single human trabecula and capture the softening curve with sufficient precision.
DOI:
10.1088/1748-0221/6/11/C11007
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Jiroušek, O.; doc. Ing. Daniel Kytýř, Ph.D.; Kunecký, J.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Němeček, J.
Publikováno:
2011, Proceedings of the Thirteenth International Conference on Civil, Structural and Environmental Engineering Computiing, Edinburgh, Civil-Comp Press), p. 1-12), ISBN 978-1-905088-46-1, ISSN 1759-3433
Anotace:
The paper presents a comparison between mechanical properties of single human trabeculae obtained by micromechanical testing and those assessed by nanoindentation. Compact uniaxial tension/compression device has been developed for this purpose. The strains at the surface of the sample are measured optically using a high-resolution CCD camera. The strain field is evaluated using image correlation technique. Local micromechanical properties were assessed using nanoindentation. From obtained nanoindentation curves material parameters for elasto-plastic constitutive model with isotropic hardening are identified in a FE simulation of the indentation process. The unknown parameters are identified in a large set of parametric studies in which the response of the model is best-fitted to the experimental curve. Validation of the material model obtained from nanoindentation is presented in simulation of the tensile test of single trabecula.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Jiroušek, O.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Kroupa, M.
Publikováno:
2011, Nuclear Instruments and Methods in Physics Research, Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, 633 (Supp. 1), p. S148-S151), ISSN 0168-9002
Anotace:
A micro-radiographic system composed of microfocus X-ray tube and a large flat panel detector has been adapted for imaging complicated internal microstructure of trabecular bone under applied deformation. To capture the deforming microstructure a load was applied in small increments while the sample was tomographically scanned. Reconstruction of the internal structure is provided using backprojection algorithm for equiangular cone-beam projection data. From the reconstructed cross-sections a finite element (FE) model of the microstructure was developed and loaded according to the experiment. Deformation behavior of the FE model was compared to the experimentally determined response of the sample.
DOI:
10.1016/j.nima.2010.06.151
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2010, Proceedings of the Seventh IASTED International Conference, Innsbruck, IASTED), p. 67-71), ISBN 978-0-88986-827-4
Anotace:
The paper deals with investigation of the trabecular bone behaviour during compression test. Paper describes loading test of trabecular bone specimen using real-time Computer Tomography scanning and its simulation by Finite Element Method. Model for the Finite Element simulation was obtained using the reconstruction from tomographic projections of the zero deformation state. Deformation states were reconstructed to assess the three-dimensional strain field in the microstructure and compared with results from FE simulations. Assessment of the material model was based on nanoindentation experiment. The nanoindentation test of the trabecular bone sample was performed and the material model was identified from FE simulation of the nanoindentation test.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.; doc. Ing. Petr Zlámal, Ph.D.; Pokorný, D.; Dammer, J.
Publikováno:
2010, Proceedings of 9th International Symposium on Computer methods in Biomechanics and Biomedical Engineering, Valencia, Universidad Politécnica de Valencia), p. 467-471), ISBN 978-0-9562121-3-9
Anotace:
The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of a sample of pelvic bone with implanted cemented acetabular component. The most unfavorable activity (downstairs walking) was simulated in two million cycles with 4Hz frequency. The process of damage accumulation in cement fixation was monitored by repeated scanning using high resolution micro-focus X-ray Computed Tomography. Use of micro-focus source and large high resolution flat panel detector allows investigation of structural changes as well as development of full-scale micro-structural models. 3D high resolution finite element model was reconstructed from the microCT data. The FE model is suitable for prediction of bone-implant interface behaviour.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.
Publikováno:
2009, Engineering Mechanics 2009 - Book of Extended Abstracts, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 314-315), ISBN 978-80-86246-35-2
Anotace:
Paper deals with investigation of trabecular bone microstructure using real-time microtomography. Recorded micro-CT scans are used to record spatial mechanical behaviour of bone under loading and provides detailed information about inner architecture and hierarchical structure of bone tissue.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.; doc. Ing. Petr Zlámal, Ph.D.
Publikováno:
2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 165-175), ISBN 978-1-905088-30-0, ISSN 1759-3433
Anotace:
This paper deals with utilization of finite element models of microstructure of complex materials with material properties obtained from nanoindentation to assess the overall material properties.Material properties at the trabecular level are obtained from nanoindentation. Parameters for the material models are obtained by fitting the experimental force-displacement curve with response obtained from the finite element simulation of the nanoindentation solved as an axisymmetric problem.The material model is used in further finite element analysis taking the microstructure into account
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Žák, O.
Publikováno:
2009, Engineering Mechanics 2009 - Book of Extended Abstracts, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 116-117), ISBN 978-80-86246-35-2
Anotace:
Paper deals with investigation of trabecular bone microstructure using real-time microtomography. Recorded micro-CT scans are used to record spatial mechanical behaviour of bone under loading and provides detailed information about inner architecture and hierarchical structure of bone tissue.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Kroupa, M.
Publikováno:
2009, Book of Abstracts 11th International Workshop on Radiation Imaging Detectors, Praha, Institute of Experimental and Applied Physics,ČVUT), p. 49-49), ISBN 978-80-01-04378-3
Anotace:
To explore the possibilities of modern X-ray detectors an experimental setup with trabecular bone sample under uni-axial load in special loading device enabling time-lapse tomography was used. The load was applied gradually and after complete tomographic scanning the deformed shape was reconstructed. Collected 3-D images help to study the deformation process of the micro-structure where collapsing of individual trabeculae can be observed and compared to finite element simulations.
Typ:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně