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:
Typ:
Článek v odborném recenzovaném periodiku

Autoři:
Dr. Afdhal Afdhal; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Dwianto, Y.B.; Palar, P.-S.
Publikováno:
2024, Materials & Design, 244, p. 1-13), ISSN 1873-4197
Anotace:
In this paper, a set of hexachiral auxetic structural designs with near zero Poisson's ratio (ZPR) characteristics is discovered via the combination of machine learning and experimentally validated finite element simulation. An active learning-enhanced Gaussian process model is utilized to generate multiple designs with near-ZPR properties and discover the boundary of the positive and negative Poisson's ratio. The results show that active learning successfully constructs a probabilistic estimation of the ZPR boundary. A comprehensive analysis of the identified ZPR contour is performed to extract crucial design insights. The findings indicate that the near-ZPR characteristic can be attained through various combinations of geometric parameters. This offers users the flexibility to select the configuration that best aligns with their specific requirements. Additionally, an investigation of the various ZPR configurations that have been discovered is carried out to understand the mechanism that yields near-ZPR property. One discovered near-ZPR design was subsequently fabricated using 3D printing for validation purposes. The experimental outcomes demonstrated a good agreement with the numerical predictions, underscoring the effectiveness of the active learning strategy in uncovering designs that closely approach ZPR conditions.
DOI:
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; González, J.A.; Park, K.C.
Publikováno:
2023, Proceedings of the 9 th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, Athens, Institute of Structural Analysis and Antiseismic Research, NTUA)
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

Autoři:
Dr. Afdhal Afdhal; prof. Ing. Ondřej Jiroušek, Ph.D.; Palar, P.S.; Ing. Jan Falta; Dwianto, Y.B.
Publikováno:
2023, Materials & Design, 232, p. 1-13), ISSN 1873-4197
Anotace:
A design exploration of hexachiral structures using explainable machine learning (ML) is performed in this work. The hexachiral structures are fabricated using resin via vat photopolymerization (VPP). The ML model is used to build the function that explains the association between Poisson’s ratio and the hexachiral design parameters. The data set for ML model construction is first collected by using the Halton sequence and simulated using the finite element method (FEM). To validate the data set, the results obtained from the FEM simulation are compared with those obtained from the compression test. The Gaussian Process Regression (GPR) models for Poisson’s ratio and porosity are constructed to extract important design insight. A Global Sensitivity Analysis (GSA) and Shapley Additive Explanations (SHAP) are used to analyze the sensitivity of the porosity and Poisson’s ratio to the hexachiral design parameters. GSA result shows that the strut’s thickness is the most decisive parameter that affects the Poisson’s ratio. The application of SHAP also reveals that the relationship between the strut thickness and Poisson’s ratio is nonlinear. Finally, the minimum Poisson’s ratio value is achieved by design with minimum strut thickness, minimum node radius, and maximum strut length.
DOI:
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

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

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

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

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

Autoři:
Ing. et Ing. Radim Dvořák; doc. Ing. Radek Kolman, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Gonzalez, J.A.; Park, K.C.
Publikováno:
2022, DD27 abstract book, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE)
Anotace:
The problem of the linear elastodynamics including domain decomposition via localized Lagrange multipliers method is solved using nite element method and direct time integration. Time integration of domains is performed separately with dierent time steps. The asynchronous integrator scheme is generalized for multiple domains problem and enhanced by the use of a local variant of the pushforward-pullback method, which eectively avoids spurious oscillation in steep stress pulses response. The proposed method is applied to the rectangular step pulse propagation problem considering the linearly varying Young modulus in space as well as the bi-material interface problem. To prove the robustness and the accuracy, the comparison with analytical solution and commercial soft- ware outputs is provided.
Typ:
Abstrakt ve sborníku z mezinár. konf. cizojazyčně

Autoři:
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:
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

Autoři:
Ing. 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:
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:
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:
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:
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:
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

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

Autoři:
Ing. Petr Koudelka, Ph.D.; Keršner, Z.; Vesenjak, M.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2020
Anotace:
The dissertation thesis is focused on the numerical modelling of the mechanical response of auxetic structures to uniaxial compressive loading. According to the primary application of auxetics in terms of deformation energy mitigation, where their unique characteristics arising from the negative Poisson’s ratio of the structure, high strain rate response is emphasised. Additionally, quasi-static characteristics are assessed to obtain reference data for the evaluation of the strain-rate dependency induced particularly by micro-inertia effects. Mechanical properties are studied using stress-strain characteristics, whereas the microstructural response is evaluated based on the function of Poisson’s ratio. In the thesis, three auxetic unit-cells having uni- or bi-axial auxetic characteristics are considered. The structures are developed by a periodic assembly of unit-cells in the respective spatial directions. Due to the complex deformation response of the auxetic structures, the reference data for the development of numerical simulations are obtained from the experiments with the samples of structures manufactured using 3D printing. Dynamic loading is performed using a Split Hopkinson Pressure Bar (SHPB) apparatus, while an approach to the numerical simulations consisting of the development of a full-scale virtual SHPB for an explicit time integration scheme in LS-DYNA was selected. In the dynamic simulations, geometrical models of the lattices precisely corresponding to the geometry of the structures for the 3D printing are used. The numerical aspects of the simulations together with the influence of the 3D printing quality on the reliability of the results are discussed. The ability of the numerical simulations to describe the deformation response of the investigated auxetic lattices is assessed based on the numerical stress-strain curves and the graphs of the strain-dependent Poisson’s ratio.
Typ:
Disertační práce (PhD)

Autoři:
Ing. Tomáš Doktor, Ph.D.; Gutermann, M.; Rusnáková, S.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2020
Anotace:
The thesis deals with the investigation of the mechanical behaviour of cellular materials at higher strain-rates and enhancement of their energy absorption capabilities. Three types of cellular solids were tested: closed- and open-cell aluminium foam and SLS printed auxetic lattices. To induce a strain-rate sensitive response in open-cell structures, different types of polymeric fillers were tested (polyurethane putty, polyurethane foam and ordnance gelatin) to form Interpenetrating- phase composites (IPCs). At the micro level, the tests were performed using an in-house apparatus in conjunction with the optical strain measurement using Digital Image Correlation (DIC). At the macro-level, for the investigation of the cellular structure a time-lapse X-ray tomography of the compression test was performed. Two types of impact tests were used to cover a broader range of the strain-rates, drop tower and Hopkinson bar (SHPB). A strain-rate sensitive response was observed at moderate strain-rates in the ordnance gelatin and IPC, while the response of unfilled aluminium foam remained unchanged. The SHPB tests showed a strain-rate sensitivity in the energy absorption for all the tested materials. The DIC strain measurement of the SHPB impact tests of the polymer-filled auxetics showed a reduction in the auxetic nature with the filling.
Typ:
Disertační práce (PhD)

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

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

Autoři:
Adorna, M.; Reis, M.; Jung, A.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, International Conference on Nonlinear Solid Mechanics - ICoNSoM2019, Palazzo Argiletum, Roma, Italy), p. 128-128)
Anotace:
In this study, two different tools for Digital Image Correlation (DIC) were used for evaluation of three-point bending tests performed using an in-house bending device. Isolated struts of an open cell aluminium foam were investigated in this study. An in-house multifunctional loading device equipped with a precise load cell with a force sensor was used to perform the bending. Experiments were observed using a pair of CCD cameras with a telecentric lense for imaging of the loading process in a sufficient quality. That enabled to perform 3D DIC evaluation using both commercial and open-source DIC software tools. Synchronisation of the cameras, the records and the stroke of the bending device was achieved using a custom Labview control software tool. Calibration of the camera pair, which was necessary for the 3D DIC evaluation, was carried out using Direct Linear Transformation (DLT). To further investigate the behaviour of the isolated struts of the aluminium foam, a photogrammetric method was used to obtain 3D models of every strut. The models allowed for a precise measurement of the struts dimensions necessary for material characteristics determination. A modified open-source Matlab tool [1] and a commercial DIC software (ISTRA 4D) were used for evaluation of the image sequences recorded by the CCD cameras. Coparison of the results obtained using both different 3D DIC tools and the results derived directly from the stroke of the measuring device are presented in this study.
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. 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:
Typ:
Stať ve sborníku z prestižní konf.

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

Autoři:
Reis, M.; Adorna, M.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A.
Publikováno:
2019, Advanced Engineering Materials, 21 (7), ISSN 1438-1656
Anotace:
Digital image correlation (DIC) is a common software tool to measure displacement and strain fields on the surface of a specimen during mechanical testing. Due to its low requirements on the experimental setup and the simple usability it is widely spread in the community of applied mechanics. Nevertheless, the real noise of the method often stays uninvestigated. Therefore, this work shows different approaches to measure errors in DIC. The present contribution proves lighting as the main error source and it shows that a series of static images allows to estimate the error level of the DIC before performing the experiment. To give a proof of concept of the improved DIC setup, three-point bending tests on single struts of aluminum foam are performed and evaluated.
DOI:
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Michaela Jurko; Ing. Petr Koudelka, Ph.D.; Ing. et Ing. Radim Dvořák; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2019, 10th International Conference Auxetics and other materials and models with ”negative” characteristics - abstract book, Poznań, Institute of Molecular Physics), ISBN 978-83-933663-8-5
Typ:
Abstrakt ve sborníku z mezinár. konf.

Autoři:
Ing. 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:
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

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

Autoři:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Jan Falta; 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:
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:
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:
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

Autoři:
Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 72-75), ISBN 978-80-01-06070-4, ISSN 2336-5382
Anotace:
Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose. In this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465HV1.019 and average Vickers hardness of ALCORAS was 36.585HV1.019.
DOI:
Typ:
Stať ve sborníku z prestižní konf.

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

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

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

Autoři:
Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Jung, A; Kumpova, I
Publikováno:
2016, Journal of Instrumentation, 11 (11), p. 1-7), ISSN 1748-0221
Anotace:
Hybrid foams are materials formed by a core from a standard open cell metal foam that is during the process of electrodeposition coated by a thin layer of different nanocrystalline metals. The material properties of the base metal foam are in this way modified resulting in higher plateau stress and, more importantly, by introduction of strain-rate dependence to its deformation response. In this paper, we used time-lapse X-ray micro-tomography for the mechanical characterization of Ni/Al hybrid foams (aluminium open cell foams with nickel coating layer). To fully understand the effects of the coating layer on the material’s effective properties, we compared the compressive response of the base uncoated foam to the response of the material with coating thickness of 50 and 75 µm. Digital volume correlation (DVC) was applied to obtain volumetric strain fields of the deforming micro-structure up to the densification region of the deforming cellular structure. The analysis was performed as a compressive mechanical test with simultaneous observation using X-ray radiography and tomography. A custom design experimental device was used for compression of the foam specimens in several deformation states directly in the X-ray setup. Planar X-ray images were taken during the loading phases and a X-ray tomography was performed at the end of each loading phase (up to engineering strain 22 %). The samples were irradiated using micro-focus reflection type X-ray tube and images were taken using a large area flat panel detector. Tomography reconstructions were used for an identification of a strain distribution in the foam using digital volumetric correlation. A comparison of the deformation response of the coated and the uncoated foam in uniaxial quasi-static compression is summarized in the paper.
DOI:
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:
Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Fíla, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2015, Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 1-12), ISBN 978-1-905088-63-8, ISSN 1759-3433
Anotace:
This paper deals with finite element modelling of auxetic cellular structures and nu- merical optimization of their effective mechanical properties. Three different auxetic structures (two-dimensional cut missing-rib, two-dimensional inverted (re-entrant) hon- eycomb and three-dimensional inverted honeycomb) were designed and produced by additive manufacturing. Fully parametric representations of the structures are devel- oped based on their geometric design and tested in a virtual finite element experiment to uncover the relationship between the overall properties and design parameters. Deformation behaviour of the selected auxetics assessed numerically is verified against experiments in which deformation is measured precisely in a large area using digital image correlation up to large strain values. Then the strain-stress curves are compared to the numerically obtained values. In the finite element analyses the geometries of the structures have been discre- tised either with three-dimensional solid elements (eight-node hexahedral elements) and with beam elements. The numerical model was equipped with the elasto-plastic material model with a von Mises yield criteria and bilinear isotropic work hardening. To inversely calculate the stress-strain relationship of the structures for large strain values both geometric and material nonlinearities were taken into account. The effects of selected structural parameters (both geometric given e.g. by relative density, rod thickness, internal angles, etc. and material given by elastic properties of the base material) are studied using parametric finite element modelling to obtain their effects on overall mechanical properties (stiffness and strength). Auxetic structures are then optimized using design parameter driven finite element models which are able to predict various effective mechanical properties such as elastic modulus, strength and Poisson’s ratio.
DOI:
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

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:
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Jung, A.; Larcher, M.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Solomos, G.
Publikováno:
2015, 11th International Conference on the Mechanical and Physical Behaviour of Materials Under Dynamic Loading, Les Ulis, EDP Sciences), ISSN 2101-6275
Anotace:
Shock absorption often needs stiff but lightweight materials that exhibit a large kinetic energy absorption capability. Open-cell metal foams are artificial structures, which due to their plateau stress, including a strong hysteresis, can in principle absorb large amounts of energy. However, their plateau stress is too low for many applications. In this study, we use highly novel and promising Ni/Al hybrid foams which consist of standard, open-cell aluminium foams, where nanocrystalline nickel is deposited by electrodeposition as coating on the strut surface. The mechanical behaviour of cellular materials, including their behaviour under higher strain-rates, is governed by their microstructure due to the properties of the strut material, pore/strut geometry and mass distribution over the struts. Micro-inertia effects are strongly related to the microstructure. For a conclusive model, the exact real microstructure is needed. In this study a micro-focus computer tomography (μCT) system has been used for the analysis of the microstructure of the foam samples and for the development of a microstructural Finite Element (micro-FE) mesh. The microstructural FE models have been used to model the mechanical behaviour of the Ni/Al hybrid foams under dynamic loading conditions. The simulations are validated by quasi-static compression tests and dynamic split Hopkinson pressure bar tests.
DOI:
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

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:
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:
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:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014
Anotace:
Bylo provedeno posouzení nosné konstrukce světelného návěstidla na provozní zatížení.
Typ:
Výzkumná zpráva v češtině

Autoři:
Ing. 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:
Ing. Petr Koudelka, Ph.D.; Jandejsek, I.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Drdácký, M.; Zíma, P.Z.
Publikováno:
2014, Journal of Instrumentation (9), ISSN 1748-0221
Anotace:
In order to ensure sustainability if historic buildings their technical state has to be inspected on regular basis. Damage assessment has to be preferably carried out using non-destructive methods otherwise damage accumulation may occur during life-cycle of the constructions. According to character of detected damage appropriate intervention measures (i.e. strengthening, consolidation, etc.) have to be then efficiently applied. Among other factors significantly influencing life span of constructions weathering agents (rain, erosion, dissolution, etc.) may cause rapid degradation of mechanical properties. In this paper X-ray radiograhical imaging was used to describe fluid penetration process in porous Maastricht limestone that is commonly used for restoration purposes. The imaging was performed in custom radiography device simulating practical in-situ measurements using microtube device. This device is a modified Karsten tube capable of determining absorbed volume and its speed even on inclined surfaces. However actual fluid penetration process in terms of saturation depth/volume ratio and shape of fluid wave propagating through microstructure is indeterminable using microtube. For this purpose real-time radiography imaging of fluid saturation process was performed to investigate behaviour of fluid in the material. Furthermore X-ray computed microtomography was performed to develop finite element model for simulation of fluid flow in the porous microstructure. Using the real-time imaging relations between penetration speed, penetration depth and penetrated volume were assessed. These results can be used to validate results from microtube measurements including nonlinear regions present when semi-spherical wave propagates through the material. Using a set of finite element simulations of the microtube experiment fluid velocity distribution in the material together with effective Darcy's flux were calculated and results were compared to those from real-time imaging.
DOI:
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014
Anotace:
The present study is focused on the investigation of mechanical behaviour of cellular materials at higher strain rates and optimisation of the material to enhance the energy absorption capabilities. The study encounters micromechanical testing, time-lapse tomography under compressive loading and moderate strain-rate loading using drop tower. Three types of material are investigated, open- and closed-cell aluminium foam and interpenetrating phase composite (IPC). The results show increase in strain energy density absorbed by IPC.
Typ:
Kandidátské minimum

Autoři:
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:
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2014
Anotace:
Pro firmu SKODA Transportation byl zpracován posudek k provedeným zkouškám střadačových brzd dodaných společností ŠKODA TRANSPORTATION a.s. ve formě Obdorného komentáře k jednotlivým provedeným zkouškám, např. měření rozměrů, tvrdosti a drsnosti povrchů jednotlivých dílů střadačové brzdy.
Typ:
Výzkumná zpráva v češtině

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Dammer, J.; Krejčí, F.
Publikováno:
2013, Journal of Instrumentation, 8 (2), ISSN 1748-0221
Anotace:
This study presents an improved radiographic method for strain measurement in very small samples of a single trabeculae. X-ray micro-radiography was used to track the deformation behaviour of individual trabecula during mechanical loading. As the X-ray micro-radiography images of a single trabecula show no significant features applicable for digital image correlation (DIC) a random pattern of markers was created on the surfaces of the samples to improve the accuracy of tracking. Metal plated borosilicate glassmicro-spheres (mean diameter 10um) were used as the markers for trabecular displacement tracking. Two different X-ray imaging setups were used for this purpose. The specimens of isolated trabeculae were loaded by amicro-mechanical testing device developed with respect to radiographical observation. This compact device enables a high precision three-point bending measurement. The specimen was continuously irradiated during the loading procedure by amicro-focus X-ray source. The radiographs were acquired by a single-photon counting silicon pixel detector and s flat panel sensor with CsI flipped scintillator plate. Circular Hough transform was used to locate positions of the spherical markers in the sequence of acquired radiographs and to calculate the strain in the loaded sample. The gold-coated micro-spheres provide clearly visible features in the sequence of radiographs after beam hardening correction, which in conjunction with pattern recognition algorithm enables to substantially improve the accuracy of strain measurements.
DOI:
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2013, UPB Scientific Bulletin, Series D: Mechanical Engineering, 75 (1), p. 161-170), ISSN 1454-2358
Anotace:
During the last decades, there has been much effort on the determination of effective elastic properties of porous metals. In this paper, the overall elastic moduli of reference aluminium foam Alporas are assessed using predictive methods based on definition of compliance contribution tensor. Surface of the foam is captured using flatbed scanner and such data is subjected to image and signal processing routines in order to obtain dimensions of the sufficient representative volume element and calculation of structural characteristics for analytical homogenization. It is shown that from all considered homogenization models only the Mori-Tanaka scheme gives results reasonably close to nominal values.
Typ:
Článek v periodiku excerpovaném databází Scopus

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

Autoři:
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:
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:
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:
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:
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Šepitka, J.; Lukeš, J.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Publikováno:
2012, Chemické listy, 106 (S3), p. 523-524), ISSN 0009-2770
Anotace:
The leech's sucking apparatus is an amazing instrument - it has 3 jaws and 300 teeth made for easily cut into the skin of the host animal. In this study, we used nanoindentation and atomic spectroscopy to reveal composition and material properties of leeches' teeth. Five samples of leech's jaws obtained from adult subjects of Hemopis sanguisuga were investigated. Main constituents of leeches' teeth have been identified. The tooth is composed mainly of calcium (41.9%), oxygen (41.2%) and carbon (11.4%), other constituents are present in small quantities (F, Na, P, 0 and S), therefore, a substance typical for mineral component in bones hydroxyapatite is likely present in the teeth among other substances. Material properties, which are independent on indentation depth, examined by nanoindentation provided average reduced modulus Er = 27.54 +/- 3.71GPa
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.
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Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 244-250), ISBN 978-1-63439-432-1
Anotace:
During the last decades, there has been much effort on the determination of effective elastic properties of porous metals. In this paper, the overall elastic moduli of reference aluminium foam Alporas are assessed using predictive methods based on definition of compliance contribution tensor. Surface of the foam is captured using flatbed scanner and such data are subjected to image and signal processing routines in order to obtain dimensions of the sufficient representative volume element and calculation of structural characteristics for analytical homogenization. It is shown that only the Mori-Tanaka scheme gives results close to nominal values.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
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:
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. 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:
prof. Ing. Ondřej Jiroušek, Ph.D.; Horníček, L.; prof. Ing. Josef Jíra, CSc.; Kunecký, J.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Vyčichl, Ph.D.
Publikováno:
2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-31-7, ISSN 1759-3433
Anotace:
This paper deals with numerical and experimental investigation of ballasted track under cyclic loading. The experimental part deals with measurement of settlements of different track bed designs under repetitive load. The designs are tested in laboratory conditions in a small-scale box filled with ballast material reinforced with different type of geosynthetics. Different thickness of the ballast and subballast layers are tested and results in terms of measured settlements at different locations are compared with FE models.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Horníček, L.; prof. Ing. Josef Jíra, CSc.; Kunecký, J.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Vyčichl, Ph.D.
Publikováno:
2009, Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 69-69), ISBN 978-1-905088-30-0, ISSN 1759-3433
Anotace:
Paper deals with numerical and experimental investigation of ballasted track under cyclic loading. The experimental part deals with measurement of settlements of different track bed designs under repetitive load. The designs are tested in laboratory conditions in a small-scale box filled with ballast material reinforced with different type of geosynthetics. Different thickness of the ballast and subballast layers are tested and results in terms of measured settlements at different locations are compared with FE models.
Typ:
Abstrakt ve sborníku z mezinár. konf.

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

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

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.; Frankeová, D.
Publikováno:
2009, 8th Youth Symposium on Experimental Solid Mechanics, Budapešť, Scientific Society of Mechanical Engineers), ISBN 978-963-9058-26-2
Anotace:
Article deals with investigation of physical and mechanical properties of trabecular bone. Non-destructive ultrasonic tests and heat measurements were used to determine the modulus of elasticity of each sample. The velocity of longitudinal ultrasonic waves' propagation depends on the mechanical properties of the material, so the Young's modulus can be obtained from the formula coupling elasticity modulus, wave velocity and bone density.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Vavřík, D.
Publikováno:
2009, Engineering Mechanics 2009 - Book of Extended Abstracts, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 166-167), ISBN 978-80-86246-35-2
Anotace:
The paper deals with microstructure investigation of trabecular bone in acetabular region. Trabecular bone microstructure is the main factor of the bone quality and mechanical propertites at macroscopic level. Data from high resolution micro Computed Tomography can be used to reconstruct the complex geometry of the trabecular bone inner structure and interface between bone and implant. The data are usable as for micro-FE modeling as well as for experimental loading tests evaluation.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. 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

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Vavřík, D.; Jakůbek, J.; Dammer, J.; Němeček, J.
Publikováno:
2008, New trends in experimental methods together with advanced numerical modelling, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 1-2), ISBN 978-80-86246-34-5
Anotace:
Article presents a combination of experimental and computational approach to determine apparent modulus of elasticity of trabecular bone. Voxel FE models with voxel size of 15 µm3 are used to calculate the overall material properties.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2008, Proc. of 79th Annual Meeting of the International Association of Applied Mathematics and Mechanics, Bremen, International Association of Applied Mattematies and Mechanics), p. 43-43)
Anotace:
One of the possibilities to study the failure behavior of trabecular bone is to use a high-resolution FEM models of trabecular structure created based on microfocus X-ray computed tomography. Material properties of the bone tissue can be obtained using e.g. nanoindentation which provides Young's modulus of elasticity with high confidence. The key part in the computational analysis of the structure is the plasticity criteria to be chosen for the tissue. In this work a thorough comparison of different plasticity criteria, both using isotropic and orthotropic hardening is presented and results in terms of overall response is given.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Jan Vyčichl, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2008, Proceedings of Workshop 2008, Praha, Czech Technical University in Prague), p. 430-431), ISBN 978-80-01-04016-4
Anotace:
The article deals with creating and analysis of interaction between pelvic bone and cemented acetabular component with imperfection in cement layer. Boundary conditions and loads were defined on contact FE models. Results from contact FE analysis of the model with ideal position of acetabular component were compared whit results from two models with imperfection in cemented layer.
Typ:
Stať ve sborníku Workshop ČVUT

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Vavřík, D.; Jakůbek, J.; Dammer, J.
Publikováno:
2008, Engineering Mechanics 2008: Book of Extended Abstracts, Praha, Ústav termomechaniky AV ČR), p. 110-111), ISBN 978-80-87012-11-6
Anotace:
For the investigation of trabecular bone microstructure and its relation to bone failure a combined approach utilizing FE models of the microstructure and compressive tests of small cylindrical samples is presented.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Kunecký, J.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2008, Proceedings of Workshop 2008, Praha, Czech Technical University in Prague), p. 480-482), ISBN 978-80-01-04016-4
Anotace:
The work is based on the Visible Human Project. Impact acceleration history is taken from MADYMO accident simulation. For the solution LS-DYNA software is used.The paper shows possibility to use detailed finite element model of human head to predict or describe injuries during mechanical loading as in this case of a traffic accident. The possibility of using combination of rigid body modeling of the whole situation together with detailed FE model of the region of interest is highly advantageous. However, the model should be verified in large number of reconstructions.
Typ:
Stať ve sborníku Workshop ČVUT

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Kunecký, J.; prof. Ing. Josef Jíra, CSc.; Horníček, L.
Publikováno:
2008, Současnost a budoucnost dopravy, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 95-98), ISBN 978-80-01-04056-0
Anotace:
Numerical investigation of bearing capacity of railway substructure using finite element method and laboratory experiments is presented. A set of parametric FE models is built and unified approach for assessment of bearing capacity of the construction presented. Results are presented in terms of design graphs, where for every type of substructure design resulting bearing capacity is evaluated. Presented methodology is easily extensible for reinforcing effects of layer inclusion, geogrid placement or use of cemented layers.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Žák, O.
Publikováno:
2008, New trends in experimental methods together with advanced numerical modelling, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 53-54), ISBN 978-80-86246-34-5
Anotace:
Article deals with material properties of spongy bone assessed by optical identification based on surface texture registration.Strains at the specimen surface were measured using high-resolution CCD camera and optical identification method was used to trace their position during deformation. Centres of gravity of the markers are then considered to be vertices of connected triangles for which fields of displacement and strain are calculated. The assessed displacements of the structure of trabecular bone are used to obtain strain-stress diagram.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.
Publikováno:
2008, Proceedings of the Sixth International Conference on Engineering Computational Technology, Stirling, Civil-Comp Press Ltd), p. 1-10), ISBN 978-1-905088-26-3
Anotace:
Microstructural Finite Element Models for the Assessment of Overall Mechanical Properties of Trabecular Bone have been studied in this paper.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Žák, O.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2008, The 7th Youth Symposium on Experimental Solid Mechanics, Wroclaw, Oficyna Wydawnicza Politechniki Wroclawskiej), p. 90-90), ISBN 978-83-7493-386-5
Anotace:
Article deals with material properties and failure criteria of trabecular bone assessed by optical identification based on surface texture registration. Trabecular bone samples of cylindrical shape are loaded in Instron 3382 loading machine. Tension and compression tests are recorded by high resolution CCD camera. Captured images are processed using Visualization ToolKit (VTK). The map is reduced to control points like ends, centres and crossing. Allocation of control points at filtered structure in every image gives information about deformation of tested sample.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Josef Jíra, CSc.; prof. Ing. Ondřej Jiroušek, Ph.D.; Horníček, L.
Publikováno:
2007, Proceedings of the Eleventh International Conference on Civil, Structural, and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), p. 1-7), ISBN 978-1-905088-17-1
Anotace:
Article deals with numerical investigation of subgrade improvement methods using geogrids. Numerical modelling for design of ballast bed construction using either traditional materials (ballast and subballast layer) with or without reinforcement using geosynthetics is presented.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Brichtová, E.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2007, Engineering Mechanics 2007, Praha, Ústav termomechaniky AV ČR), p. 107-108), ISBN 978-80-87012-06-2
Anotace:
The paper deals with reconstruction of a sport accident using detailed FE model of skull and brain. The injury to be reconstructed was a sport accident involving a 12-year old boy on whom a handball cage fell during school sport activity. Presented human head model was developed using series of CT scans obtained postsurgically. Rigid body model representing the boy was used to assess initial conditions which were used in finite element modeling of the head impact. From the rigid body modeling a comparison of different approaches to head injury prediction is drawn.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Němeček, J.
Publikováno:
2007, Proceedings of the Ninth US National Congress on Computational Mechanics, Weiheim, Wiley - VCH Verlag), p. 62-62), ISSN 1617-7061
Anotace:
Microfocus X-ray computed tomography is used to reconstruct the structure of trabecular bone sample to develop a FEM model of high-resolution. Material properties used in the FEM model are obtained from nanoindentation experiments. Plasticity model with isotropic hardening is used with tissue yield stress set according to results from mechanical testing of cylindrical specimens.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Kunecký, J.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2007, Engineering Mechanics 2007, Praha, Ústav termomechaniky AV ČR), p. 149-150), ISBN 978-80-87012-06-2
Anotace:
To investigate the possibility of improvement of the protective properties at higher speeds a parametric study of numerical model of ski helmet was made. Numerical model of the helmet was created using CAE methods, the FE analysis was performed in LS-DYNA environment. Comparison of results was made using HIC value (probability of head/brain injury).
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Brichtová, E.
Publikováno:
2007, From Horse-drawn Railway to High-speed Transportation Systems, Praha, Czech Technical University in Prague), p. 111-112), ISBN 978-80-01-03699-0
Anotace:
Detailed Finite Element Model of human head used for head injury assessment is presented in the article. Development of the model based on a series of postoperative CT images of high resolution is shortly described. The model is used in a model situation of a sport accident involving a 12-year old boy on whom a handball cage fell during a sport activity causing a serious injury of the boy's head. An approach to quantify the injuries caused is described in the paper.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Jan Vyčichl, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2006, 2st Students' Scientific Conference of Biomechanics, Wroclaw, Oficyna Wydawnica Politechniki Wroclawskiej), p. 73-74), ISSN 1732-0240
Anotace:
The article deals with creating high resolution FE model of pelvic bone and acetabular component (cemented and cementless). The contact between component and pelvic bone was created and the model was loaded by quasi-static joint forces, representing the individual stance phase of gait. The FE model was used to ascertain the contact stress conditions in the underlying subchondral bone.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2006, Fourth International IASTED Conference on BIOMECHANICS, Gran Meliá Salinas, Lanzarote, IASTED), p. 142-147), ISBN 0-88986-604-X
Anotace:
Paper presents a study conducted to validate a finite element model of human skull in brain response due to frontal and lateral impacts. The brain is modelled as a homogeneous inviscid fluid. Maximal values of intracranial pressure and shear stress distributions predicted from FE simulations were compared to values obtained from experiments done by other authors.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Kunecký, J.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2006, 2st Students' Scientific Conference of Biomechanics, Wroclaw, Oficyna Wydawnica Politechniki Wroclawskiej), p. 91-92), ISSN 1732-0240
Anotace:
In the paper a numerical model of dummy head form enclosed in a motorcycle helmet is presented. The model was developed using the Non-Uniform Rational B-splines (NURBs). The solution was performed using Finite Element Method with explicit time integration scheme (LSDYNA solver) which is well suited for analysis of impact and highly non-linear problems. The model can be used for design, optimization and testing of motorcycle helmets.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Kunecký, J.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2006, Engineering Mechanics 2006, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 208-209), ISBN 80-86246-27-2
Anotace:
Head injuries are the most often causes of death in traffic accidents. To develop better interiors of cars or new protective devices (e.g. helmets) there is a need to quantify the mean criteria of injury. Most of today used head injury criteria use an integral value of acceleration of the head during a certain time interval. The main drawback of these criteria is the fact, that they use only linear acceleration of the head. For better HIC assessment there is a need to use different measures, e.g. combination of translational and rotational acceleration or criteria based on strain energy. For these purposes complex FE models are used. To verify the behavior of these FE models, drop tests with different drop height are usually used. The paper presents results of drop tests used to validate FE models of human head. According to data obtained from accelerometers the HIC was computed and the critical height was determined.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Kunecký, J.; prof. Ing. Ondřej Jiroušek, Ph.D.; Zelenková, K.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2006, 14th ANSYS Users´Meeting, Brno, SVS FEM), p. 21-24), ISBN 80-239-7764-4
Anotace:
Article deals with cancellous bone material properties determination comparing to results of FE model based on CT scanning. Speciments are gained from fresh pig's heads of femur. Speciments are drilled in dorection of main loading and in other two normal direction. There were Instron 3382 loading machine for tension test and Nicon camera for optical dentification method at experiment set up. Results of those experiments are displayed on standard stress-strain graph and Young modulus is determined. Young modulus results are suited for biomechanicel FE models and the experimental method could be used for human testing.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2006, Engineering Mechanics 2006, Praha, Ústav teoretické a aplikované mechaniky AV ČR), p. 140-141), ISBN 80-86246-27-2
Anotace:
Paper presents a detailed finite element model of human head used for head injury criteria assessment. Today most used HICs are based on the history of linear acceleration only. However, the rotational acceleration plays also important role, due to the rupture of bridging veins involved in the relative motion between the skull and the brain. Presented model allows for new approach to define the HIC based on either strain energy or on combination of linear and rotational acceleration history. The model is based on a series of CT and MRI scans of a cadaver head of high resolution and is composed of three different regions: (i) skull, (ii) brain and (iii) subarachnoidal space. Discussion on material properties of these four distinct regions is given in the paper.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Jan Vyčichl, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2006, Engineering Mechnaics 2006, Praha, Academy of Sciences of the Czech Republic), p. 347-348), ISBN 80-85918-93-5
Anotace:
The article deals with contact stress analysis of pelvic bone after implantation of cemented acetabular component with imperfections of cemented layer. 3D high resolution FE model of pelvic bone was created from the sequence of CT-slices. Imperfections were created both in the cement layer and in the bone tissue by drilling fixation holes. Boolean operations were used for inserting the spherical cemented component. Two contacts were defined in the FE model. The first contact is defined between the cement layer and the pelvic bone and the second one is between the cement layer and the polyethylene cup. The model was loaded by quasi-static joint forces, representing the maximum value of stance phase of gait \cite{Bergmann-HIP98}. The FE model was used to ascertain the contact stress conditions in the underlying subchondral bone.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Jan Vyčichl, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2005, 13. ANSYS User´s Meeting, Brno, SVS FEM), p. 321-329), ISBN 80-239-5675-2
Anotace:
Článek se zaměřuje na problematiku vlivu různých typů acetabulárních komponent na velikost a charakter kontaktního napětí v pánevní kosti. Popisuje tvorbu geometrického a následně i MKP modelu pánevní kosti s implantovanou acetabulární komponentou, jejich vzájemnou interakci a způsob upevnění a zatížení tohoto modelu s využitím softwaru ANSYS. V závěru tohoto článku jsou výsledky kontaktní analýzy zhodnoceny a porovnány.
Typ:
Stať ve sborníku z lokální konf. česky

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2005, Engineering Mechanics 2005, Praha, Ústav termomechaniky AV ČR), p. 193-194), ISBN 80-85918-93-5
Anotace:
Methods for fully-automatic generation of FE model are shortly discussed in the paper. There are two basic principles of reconstruction, voxel-based and volume-based methods. The voxel model generation is based on checking all pixel values and defining voxels by means of the selected pixels. Development of the volume model is usually divided into three procedures: tissue segmentation, contour model definition and surface area definition. Three FE models of femur were considered: (i) cortical model (ii) spongio-cortical model with homogeneous cancellous tissue (iii) spongio-cortical model with heterogeneous cancellous tissue. These models were compared in a simple stress analysis. FE analyses results of all these models are compared with results of experiments conducted using fresh cadaver femur and strain-gauge measurement.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2005, GESA-Symposium 2005 Strukturanalyse, Darmstadt, VDI/VDE Gesellschschaft- und Automatisierungstechnik (GMA)), p. 463-472), ISBN 3-18-091899-3
Anotace:
A comparison between experimental investigation of an impact of human skull and finite element modelling of the free fall using Finite Element Method (FEM). The experiments consist of a series of drop tests conducted using a metal head form instrumented with an accelerometer. These tests are used to investigate protective capacity of helmets. The FE simulations use a detailed three-dimensional model of human skull, which was developed based on a series of computer tomography scans of 512x512 pixel resolution taken at 1mm distances. The FE model of human skull was filled with a simplified model of human brain.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2005, Engineering Mechanics 2005, Praha, Ústav termomechaniky AV ČR), p. 145-146), ISBN 80-85918-93-5
Anotace:
Article deals with explicit finite element modelling of contact onditions of human head impacting a flat rigid surface. For this purpose, detailed 3-D model of human skull and brain was developed based on a series of computer tomography scans of resolution 512x512 pixels taken at 1 mm distances. The FE model of human skull was filled with simplified model of human brain. The brain is modelled as a homogeneous viscoelastic material. A case study of low-velocity impact to different regions of the human head (e.g. frontal impact and impact in the occipital region) is also modelled.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2005, Second IASTED International Conference on Biomechanics, Benidorm, Acta Press), p. 211-214), ISBN 0-88986-534-5
Anotace:
The article reports on development of FE model of pelvic bone from a series of CT scans of high resolution. This model is used in comparative study of contact conditions between several types of acetabular components currently used in the Czech Republic. Procedure of development of the surface model as well as the generation of tetrahedral element of high quality is shortly discussed. After a thorough validation of the FE model in a sensitivity analysis using loading from a daily activity of the average individual, this model will be used to compare several different types of acetabular cups as well as to investigate possibilities of implant optimal position estimation.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Jan Vyčichl, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2005, Engineering Mechanics 2005, Praha, Ústav termomechaniky AV ČR), p. 347-348), ISBN 80-85918-93-5
Anotace:
Práce se zabývá porovnáním vlivu geometrie různých typů acetabulárních komponent na charakter kontaktního napětí v pánevní kosti při normální chůzi. Pro tento účel byl vytvořen ze sekvence 240 CT snímků detailní MKP model pánevní kosti a tři MKP modely acetabulárních komponent. Ty odpovídají v současnosti nejužívannějším typům implantátů používaných při totální endoprotéze kyčelního kloubu.
Typ:
Stať ve sborníku z lokální konf. česky

Autoři:
Kunecký, J.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2005, 13. ANSYS User´s Meeting, Brno, SVS FEM), p. 151-157), ISBN 80-239-5675-2
Anotace:
Příspěvek popisuje tvorbu numerického modelu lidské lebky na základě dat získaných z počítačové tomografie spolu s jeho následnou numerickou analýzou. Postupy rekonstrukce jsou zautomatizovány a provedeny mimo prostředí ANSYSu, do kterého je zrekonstruovaný model importován pomocí standardních příkazů preprocesoru PREP7. Lebka je modelována pomocí sendvičového materiálového modelu kosti lebky, který dobře vystihuje její strukturu. Toho je docíleno pomocí skořepinových prvků, kterými je v preprocesoru pokryt importovaný model. Tlouštka této vrstvy je v práci testována a určena na základě několika výpočtů s různými hodnotami tlouštky skořepiny (při neměnné geometrii původního modelu). Porovnáním s výsledky obdobně provedených pokusů publikovaných v literatuře je vyhodnocena nejlepší varianta složení lebky. Vlastní analýza je uvažována jako simulace nárazu provedená pomocí statického zatížení, které odpovídá maximální naměřené síle při dynamickém zatížení.
Typ:
Stať ve sborníku z lokální konf. česky

Autoři:
prof. Ing. Josef Jíra, CSc.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2004, Proceedings of the Second IASTED International Conference on Biomechanics, Anaheim, Acta Press), p. 130-133), ISBN 0-88986-448-9
Anotace:
The finite element models of the inner organs (pelvis, skull, long bone) are developed from the series of computer tomography scans and include material properties based on apparent density of the tissue. A standard procedure consisting of image tresholding and determining the bone outer and inner surfaces using the marching cubes algorithm is used for reconstruction. The migration of acetabular cup into the pelvis is investigated. The FE model of the skull is used for numerical modelling of a head impact during traffic accidents. The FE models of long bones enable to predict their failure load.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2004, Experimental Stress Analysis 2004, Plzeň, Škoda Výzkum), p. 105-108), ISBN 80-239-2964-X
Anotace:
Finite element models of parts of human skeletal system are nowadays constructed on basis of data obtained from Computed Tomography or Magnetic Resonance images. Material properties of cancellous bone have been found to be strongly dependent on apparent density of the tissue. Experimental procedures used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape will be described and relationship between the apparent density and Young's modulus of elasticity as well as ultimate strength are proposed. Compressive and tensile specimens are used while for the strains are measured using an optical method utilizing CCD camera of high resolution.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Kunecký, J.
Publikováno:
2004, 1st Students' Scientific Conference of Biomechanics, Wroclaw, Oficyna Wydawnicza Politechniki Wroclawskiej), p. 105-106), ISSN 1732-0240
Anotace:
With increasing power of computers and accordingly developing variational methods, especially Finite Element Method (FEM), computer simulation is nowadays one of the most popular methods in engineering practice. The major advantage of computer simulations compared to experiments is that they are cheaper and always non-destructive. For needs of biomechanics, we can consider analyzes of parts of skeleton or simulations of blood flow etc. For numerical analysis using FEM development of accurate geometry of organs of different tissues is necessary. An example of use in biomechanics is stress analysis of bones, in our case human skull. The problem is divided into two parts: image analysis and tissue segmentation followed by reconstruction of the model geometry. The latter can be achieved by two different approaches with the same goal (FE model): volume generation using NURBS (Non-Uniform Rational B-Splines) used for reconstruction of organs of relatively simple shape (e.g. femur) and direc
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Josef Jíra, CSc.; Máca, J.
Publikováno:
2004, Seventh International Conference on Computational Structures Technology, Lisboa, Technical University of Lisbon), p. 221-222), ISBN 0-948749-93-8
Anotace:
The article reports on development of finite element models of parts of human musculosceletal system based on data obtained from Computer Tomography and Magnetic Resonance Imaging. Methods used for automatic tissue segmentation, contour extraction and surface detection are described in the paper. Methods for surface mesh simplification (mesh decimation) as well as topology optimization are discussed, too. Spatial discretization of the three-dimensional space are based on Delaunay tetrahedralization followed by shape optimization. The shape optimization is based on Laplace smoothing and local mesh improvements, such as edge swap or edge split procedures.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2004
Anotace:
The thesis deals with the algorithms for automatic generation of finite element models on basis of the data obtained from medical imaging systems in general. The described algorithms work in general for any organ and any medical imaging technique, but special emphasis has been given to construction of parts of the skeletal system.
Typ:
Disertační práce (PhD)

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2004, Experimental Methods and Measurement Techniques in Monitoring and Supervising Engineering Structures and Thein Numerical Analysis, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 39-42), ISBN 80-86246-20-5
Anotace:
Experimental procedures utilizing an optical identification method used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape are described in the paper. To measure very small strains of the cancellous bone, high-resolution CCD-camera and algorithm making use of sub-pixel determination of the centre-of-gravity of the markers are used. The experimental procedures serve for consequent evaluation of the relationship between apparent density and Young's modulus of elasticity and ultimate strength of the cancellous bone.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Vyčichl, J.
Publikováno:
2004, 1st Students' Scientific Conference of Biomechanics, Wroclaw, Oficyna Wydawnicza Politechniki Wroclawskiej), p. 73-74), ISSN 1732-0240
Anotace:
The article deals with methods for tissue segmentation and contour detection procedures in a sequence of slices used for construction of mathematical model used for stress analysis using the Finite Element Method (FEM). This process involves modification of the input data obtained from medical imaging systems and image processing
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Josef Jíra, CSc.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Micka, M.
Publikováno:
2004, Proceedings of the Seventh International Conference on Computational Structures Technology, Stirling, Civil-Comp Press Ltd), p. 10101-10112), ISBN 0-948749-94-6
Anotace:
The paper deals with loosening and migration of cementless acetabular cups into the pelvis that belongs to the most serious therapeutic complications arising sometimes several months to years after operation. The aseptic loosening of the cup is mainly influenced by two mechanical factors: ultrahigh molecular weight (UHMW) polyethylene wear and initial cancellous bone stresses. The geometry of the acetabular cups was designed directly in ANSYS and imported to the database file containing the geometry of the pelvic bone generated from the CT scans. Research was concentrated on the analysis of contact stresses and strains.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Máca, J.
Publikováno:
2004, Engineering Mechanics 2004, Praha, Ústav termomechaniky AV ČR), p. 133-134), ISBN 80-85918-88-9
Anotace:
The article reports on procedures used for development of FE models of bones on basis of data obtained from series of computed tomography (CT) scans. These models include mechanical properties reflecting the bone inhomogeneity through apparent density which can be easily retrieved from the CT scans. Experimental procedures used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape were designed in such a way, which allows for determination of the viscoelastic properties of cancellous bone. Both compressive and tensile specimens are tested while for the strain measurement an optical method utilizing CCD camera of high resolution is used. Relationship between the apparent density and mechanical properties of cancellous bone in a power-law form is proposed.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Josef Jíra, CSc.; prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2003, Engineering Mechanics 2003, Praha, AV ČR, Ústav teoretické a aplikované mechaniky), p. 1219-1222), ISBN 80-86246-18-3
Anotace:
Metodika tvorby výpočtového modelu lidské lebky z dat získaných z počítačové tomografie, který bude použit pro výpočet napjatosti při extrémním zatížení
Typ:
Stať ve sborníku z mezinár. konf. česky

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Vavřík, D.
Publikováno:
2003, Biomechanics 2003, Rhodes, IASTED), p. 109-114), ISBN 0-88986-359-8
Anotace:
The article reports on development of experimental procedures used for evaluation of mechanical properties of cancellous bone using small samples of cylindrical shape. The procedure utilizes a method of optical identification for measuring the bone strains, enabling to avoid problems with extensometer placement and to detect problems with specimen fixture.The method is also usable for evaluation of viscoelastic properties of the cancellous bone. Both compressive and tensile specimens are tested while for the strain measurement an optical method utilizing CCD camera of high resolution is used. The procedure will be further used to validate finite element models of whole bones with material properties based on the apparent density in Hounsfield units obtained from computer tomography scans and to assess the usability of those models to predict the whole bone failure under different loading conditions
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2003, Acta of Bioengineering and Biomechanics, 5 (1), p. 214-217), ISSN 1509-409X
Anotace:
The paper reports on development process of finite element models of human skull used in investigation of extreme stress state during a traffic accident. The procedures used in the development of the geometry of the skull from the series of computer tomography scans are shortly described and simplified FE-models presented. Results from a simple FE analysis using several models of different resolution are compared to estimate optimal number of degrees of freedom and to develop a numerically optimal model of human skull. The finite element models will be mainly used for evaluation of parameters that are necessary for protective helmet design.
Typ:
Článek v odborném recenzovaném periodiku

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2003, Doprava a telekomunikace pro 3. tisíciletí, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 71-74), ISBN 80-01-02741-4
Anotace:
Článek se zabývá návrhem a realizací svazku počítačů pro náročné numerické výpočty. Optimalizace svazku typu Beowulf pro distribuované výpočty pomocí MPI pro řešení rozsáhlých soustav lineárních i nelineárních algebraických rovnic
Typ:
Stať ve sborníku z fakultní konference česky

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Vavřík, D.
Publikováno:
2003, Engineering Mechanics 2003, Praha, AV ČR, Ústav teoretické a aplikované mechaniky), p. 1200-1203), ISBN 80-86246-18-3
Anotace:
Vývoj experimentálního zařízení pro měření mechanických vlastností spongiózní kosti za použití malých vzorků válcového tvaru. Tahové i tlakové zkoušky jsou prováděny pomocí zatěžovacího stroje Instron 4301,kdy deformace jsou měřeny pomocí velmi citlivé optické metody za použití CCD kamery s vysokým rozlišením. Postup slouží ke stanovení vztahu mezi relativní hustotou kostní tkáně získané z počítačové tomografie a vískoelastickými vlastnostmi, které jsou nutné pro další numerická modelování
Typ:
Stať ve sborníku z mezinár. konf. česky

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2002, FEM Workshop 2002, Ulm, University of Ulm), p. 95-101), ISBN 3-9806183-5-8
Anotace:
Article presents a study of the possible mechanical reasons for the acetabularcup migration which is one of the main causes for total hip replacement (THR) instability and leads to an early re-operation. Micromotion due to the bone resorption causing changes in the stress distribution is studied as the main reason for the initiation of the acetabular cup migration. Detailed FE model of the cup is constructed and a short discussion about appropriate contact algorithm (face-to-face contact elements) is given.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Matlach, R.; doc. Ing. Jitka Jírová, CSc.
Publikováno:
2002, Biomechanics of Man 2002 (BMC 02), Praha, Czech Society of Biomechanics), p. 213-216), ISBN 80-86317-23-4
Anotace:
Acetabular Cup Migration is Studied in a Preliminary Biomechanical Study Using Parametric Finite Element Models of Pelvic Bone Constructed From CT-Data and Several Types of Acetabular Components Implanted Into the Pelvic Bone Usingstandard Boolean Operations. UHWMPE Wear of the Acetabular Cup is Also Estimated Using Frictional Contact Elements With Large Sliding.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.; doc. Ing. Jitka Jírová, CSc.; Kult, J.
Publikováno:
2002, 10. ANSYS User's Meeting, Brno, SVS FEM), p. 1-6), ISBN 80-238-9394-7
Anotace:
Study of the Possible Mechanical Reasons For the Acetabular Cup Migration Which is one of the Main Causes for Total Hip Replacement (THR) Instability and Leads to an Early Re-Operation. The First Possible Reason For this Phenomena can be Explained by the Wear Volume of the Ultra High Molecular Weight Polyethylene (UHWMPE) Acetabular Cup. The Second Reason For the Acetabular Cup Migration is Excessive Cancellous Bone Stress. Both Influences Are Studied For Several Types of Prosthesis Using a Detailed FE-Model of the Pelvic Bone Constructed Using Data Obtained From Computer Tomography (CT)Scans.
Typ:
Vyzvaná předn. uvedená ve sborníku z mezinárodní konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; doc. Ing. Jitka Jírová, CSc.; Matlach, R.
Publikováno:
2002, Acta of Bioengineering and Biomechanics. Proceedings of the 13th Conference of European Society of Biomechanics, Wroclaw, Oficyna Wydawnicza Politechniki Wroclawskiej), p. 139-140), ISBN 83-7085-639-X
Anotace:
The Aim of the Work is to Describe the Possible Relationship Between the Mechanical Fracture of Different Types of Bone in Relation to Different Kinds of Mechanical Loading. For the Assessment of the Critical Values of Failure Load Under Different Loading Conditions Both Mechanical Testing in Vitro and Numerical Modeling is Used. Finite Element Models Are Constructed on the Basis of Data Obtained From Computer Tomography and Include Material Properties Based on Apparent Density of the Tissue.
Typ:
Vyzvaná předn. uvedená ve sborníku z prestižní konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Máca, J.; prof. Ing. Josef Jíra, CSc.
Publikováno:
2001, Acta of Bioengineering and Biomechanics, 3 (1), p. 59-73), ISSN 1509-409X
Anotace:
For the Needs of Forensic Medicine the Knowledge of Mechanical Behavior of the Whole Bones is of High Importance. Mechanical Properties, Such as Young's Modulus of Elasticity and Poisson's Ratio Have Already Been Measured Using Small Pieces of Bones, Which is For the Needs of Forensic Medicine Useless. Moreover, these Characteristics Are Age-Dependent and Therefore Usually Considered as the Average Comparative Values. The Aim of the Work is to Describe the Possible Relationship Between the Mechanical Fracture of the Bone in Relation to Age and Sex For Different Bones and Types of Mechanical Loading. For the Assessment we use Both Mechanical Testing in Vitro and Mathematical Modeling.
Typ:
Článek v odborném recenzovaném periodiku

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2001, Advances of Measurement Techniques and Experimental Methods in Engineering Sciences, Wuppertal, Bergische Universität), p. 25-26)
Anotace:
The Material Properties to be Used in Finite Element Modelling are Obtained Using Simple Mechanical Tests. The Geometry of Our Numerical Models is Constructed Based on Computer Tomography Scans and the Models Have Material Properties Based on Apparent Density Values Included in Those CT-Scans.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Jírová, J.; Matlach, R.
Publikováno:
2001, Experimental Stress Analysis 2001, Praha, Institut teoretické a aplikované mechaniky), p. 145-148), ISBN 80-86246-09-4
Anotace:
For the Needs of Forensic Medicine the Knowledge of Mechanical Behavior of the Whole Bones is of High Importance. Mechanical Properties, Such as Young's Modulus of Elasticity and Poisson's Ratio Have Already Been Measured Using Small Pieces of Bones, Which is For the Needs of Forensic Medicine Useless. Moreover, these Characteristics Are Age-Dependent and Therefore Usually Considered as the Average Comparative Values. The aim of the Work is to Describe the Possible Relationship Between the Mechanical Fracture of the Bone in Relation to Age and Sex For Different Bones and Types of Mechanical Loading. For the Assessment we use Both Mechanical Testing in Vitro and Mathematical Modeling.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2001, Přehled výsledků a úspěšných publikací dosažených s podporou IBM RS 6000/SP, Praha, České vysoké učení technické v Praze, Výpočetní centrum), p. 155-159), ISBN 80-01-02334-6
Anotace:
Several Algorithms for Construction of Mathematical Models For the Finite Element Method Were Compared in Example of Stress Analysis of a New Type of Implant Used in Finger Reconstruction Surgery. The Mathematical Model of Proximal Phallang was Constructed and Material Characteristics For the Cortical Bone Were Obtained From the Apparent Density in Hounsfield Units.
Typ:
Kapitola v vědecké knize cizojazyčně

Autoři:
Jírová, J.; prof. Ing. Ondřej Jiroušek, Ph.D.; Kult, J.
Publikováno:
2001, ISBN 80-86246-09-4
Typ:
Sborník z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; prof. Ing. Josef Jíra, CSc.; Jírová, J.; Kult, J.
Publikováno:
2001, 9th ANSYS Users Meeting, Brno, SVS FEM), p. 1-6)
Anotace:
The contribution Reports on Problems Solved by a Laboratory of Biomechanics Team Using Numerical FEM System Ansys. The First Problem is a Complex Analysis of Swanson's Prosthesis of Interphalangeal Joint and its Interaction With Phalangeal and Metacarpal Bone. Nonlinear Hyperelastic Material Model and Contact Elements Were Used. The Second Analysis is From the Application of Biomechanics in the Field of Forensic Medicine, Experimental and Numerical Approach to Determination of Ultimate Strength of Bones is Shortly Described. The Material of the Bone is Considered Nonlinearly Elastic With Varying Material Properties Based on Data Obtained From Computer Tomography Scans.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2000, International Conference Engineering Mechanics 2000, Praha, AV ČR, Ústav teoretické a aplikované mechaniky), p. 39-42), ISBN 80-86246-04-3
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Kult, J.; Máca, J.
Publikováno:
2000, CTU Reports: Contributions to Mechanics of Materials and Structures, Praha, České vysoké učení technické v Praze), p. 105-118), ISBN 80-01-02320-6
Typ:
Stať ve sborníku z lokální konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2000, Biomechanics of Man 2000, Olomouc, Univerzita Palackého), p. 60-63), ISBN 80-244-0193-2
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2000, 12th Conference of the European Society of Biomechanics, Dublin, Royal Academy of Medicine), p. 368-368), ISBN 0-9538809-0-7
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
prof. Ing. Ondřej Jiroušek, Ph.D.; Jírová, J.
Publikováno:
2000, 8. ANSYS Users Meeting, Brno, SVS FEM), p. 1-4)
Typ:
Stať ve sborníku z mezinár. konf. česky

Autoři:
Micka, M.; Jírová, J.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
1998, Engineering Mechanics 98, Praha, AV ČR, Ústav termomechaniky), p. 471-476), ISBN 80-85918-40-4
Typ:
Stať ve sborníku z mezinár. konf. česky