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

rozklikni NABÍDKU

Publikace

informace pocházejí z univerzitní databáze V3S

Autoři:
Mauko, A.; Emre Yilmaz, Y.; Novak, N.; Ing. Tomáš Doktor, Ph.D.; Vesenjak, M.; Ren, Z.
Publikováno:
2024, Composite Structures, 333, p. 1-10), ISSN 0263-8223
Anotace:
The study presents an extensive mechanical and computational characterisation of novel cellular metamaterial with axisymmetric chiral structure (ACS) at different strain rates. The Direct Impact Hopkinson Bar (DIHB) testing device was used for impact testing up to 21 m/s striker speed, which was insufficient to reach the shock deformation regime. Thus, using computational simulations to estimate the structure behaviour at high strain rates was necessary. Experimental and computational results showed that all ACS structures exhibit a nominal stress–strain relationship typical for cellular materials. As the loading conditions shifted to a dynamic regime, the micro–inertia effect became increasingly pronounced, leading to a corresponding rise in structure stiffness. The Poisson's ratio in all ACS increases gradually, making them superior to traditional cellular materials, which experience a sudden increase in Poisson's ratio during loading. Additionally, the study found that the structures exhibited a rise in the auxetic effect with an increase in strain rate, highlighting the benefits of axisymmetric structures in high-loading regimes. Overall, the obtained results provide valuable insights into the mechanical properties of ACS under different loading regimes and will contribute to further design improvements and the fabrication of novel ACS metamaterials.
DOI:
10.1016/j.compstruct.2024.117949
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

Autoři:
Novak, N.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Václav Rada; Ing. Tomáš Doktor, Ph.D.; Al-Ketan, O.; Rowshan, R.; Vesenjak, M.; Ren, Z.
Publikováno:
2022, Materials Science and Engineering A - Structural Materials: Properties, Microstructure and Processing, 852 (5), ISSN 0921-5093
Anotace:
One of the most promising options for future crashworthiness applications is thin-walled tubes filled with various cellular materials (e.g. metal foam). Of higher interest are the shell-based lattices, which have lately gained popularity due to their superior qualities over strut-based lattices. In this work, we investigate the mechanical response of foam-filled tubes where the tube's core was represented by Triply Periodic Minimal Surface (TPMS) diamond lattices. Samples made of stainless steel 316L comprising the diamond lattice core, empty tubes, and in-situ TPMS-filled tubes were additively manufactured and mechanically tested under compressive loading. As-fabricated welded tubes and ex-situ TPMS-filled tubes were also analysed and compared. Under the axial loading, the ex-situ and in-situ TPMS-filled tubes showed very similar behaviour. Enhanced energy absorption up to 21% and 44% compared to the sum of empty tubes and the core responses was noted. The energy absorption enhancement of 12% in the case of transversal loading is limited to in-situ TPMS-filled tubes, where the connection between the tube and core prevents the tube's walls from buckling. Computational models with homogenised core were developed and validated based on the experimental data. These straightforward, fast, and accurate computational models can be efficiently used for large-scale real-life applications, e.g. crash and impact.
DOI:
10.1016/j.msea.2022.143680
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

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

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

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

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

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

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

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

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

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

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

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

Autoři:
Ing. Nela Krčmářová; Ing. Jan Šleichrt, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2017, ExNum 2016, Praha, CESKE VYSOKE UCENI TECHNICKE V PRAZE), p. 72-75), ISBN 978-80-01-06070-4, ISSN 2336-5382
Anotace:
Metal foams are innovative porous material used for wide range of application such as deformation energy or sound absorption, filter material, or microbiological incubation carrier. To predict mechanical properties of the metal foam is necessary to precisely describe elasto–plastic properties of the foam on cell–wall level. Indentation with low load is suitable tool for this purpose. In this paper custom designed instrumented microindentation device was used for measurement of cell-wall characteristics of two different aluminium foams (ALPORAS and ALCORAS). To demonstrate the possibility of automated statistical estimation of measured characteristics the device had been enhanced by semi-automatic indent positioning and evaluation procedures based on user-defined grid. Vickers hardness was measured on two samples made from ALPORAS aluminium foam and one sample from ALCORAS aluminium foam. Average Vickers hardness of ALPORAS foam was 24.465HV1.019 and average Vickers hardness of ALCORAS was 36.585HV1.019.
DOI:
10.14311/APP.2017.7.0072
Typ:
Stať ve sborníku z prestižní konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Tomáš Doktor, Ph.D.; Kumpová, I.; Koudelková, V.; Nepomucká, K.; Šepitka, J.; Gantar, A.
Publikováno:
2017, 25th INTERNATIONAL CONFERENCE ON MATERIALS AND TECHNOLOGY - PROGRAM AND BOOK OF ABSTRACTS, Ljubljana, Inštitut za kovinske materiale in tehnologije), ISBN 978-961-94088-1-0
Anotace:
The microtomography inspection was performed using the patented (European patent no. EP2835631) in-house designed modular radiographical imaging device equipped with scintillators, large single photon counting and spectroscopic detectors. From reconstructed volumetric data internal microarchitecture, porosity, cell-wall thickness and BAG distribution was derivated. The results were compared with the results of the planar analysis of thin scaffold layers prepared by cryosection.
Typ:
Abstrakt ve sborníku z mezinár. konf.

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

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

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Adorna, M.; Ing. Michaela Jurko; Ing. Jan Šleichrt, Ph.D.; Ing. Nela Krčmářová; Gantar, A; Novak, S
Publikováno:
2016, Engineering Mechanics 2015, Zurich, TRANS TECH PUBLICATIONS LTD), p. 665-670), ISSN 1662-7482
Anotace:
This work presents deformation behaviour of gellan gum and gellan gum - bioactive glass composites as novel hydrophilic materials for production of scaffolds in the field of bone-tissue engineering. According to recent studies such materials are attractive for personalized design of implants thanks to their biocompatibility and wide range of available fabrication methods. Batch of samples was subjected to uni-axial compression loading in a custom designed loading device to obtain their elastic and plastic characteristics. However the testing procedure was challenging because of very low stiffness of the material acquired results show a significant reinforcement effect of bioactive glass and its influence to the elastic modulus.
DOI:
10.4028/www.scientific.net/AMM.821.665
Typ:
Stať ve sborníku z mezinár. konf.

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

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šepitka, J.; Lukeš, J.
Publikováno:
2015, Proceedings of the 11th Conference on Local Mechanical Properties, Uetikon-Zurich, Trans Tech Publications), p. 129-133), ISBN 978-3-03835-555-7, ISSN 1013-9826
Anotace:
This paper deals with evaluation of mechanical properties of human trabeculae in the interconnection area. Local changes in the trabecular connections were evaluated using both quasi-static nanoindenation and modulus mapping technique. Connecting point of two trabeculae was revealed by precise grinding and polishing. A rectangular region in the interconnection was selected and inspected by modulus mapping procedure. Moreover several quasi-static indentation measurements using cube-corner indenter were performed along distinct lamellae. The obtained elastic properties were then compared with the values of the rod-like trabeculae. The comparison does not indicate significant differences in elastic properties between the trabecular rods and interconnections.
DOI:
10.4028/www.scientific.net/KEM.662.129
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

Autoři:
Ing. Petr Koudelka, Ph.D.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Nela Krčmářová; Šepitka, J.; Lukeš, J.
Publikováno:
2015, Proceedings of the 11th Conference on Local Mechanical Properties, Uetikon-Zurich, Trans Tech Publications), p. 138-141), ISBN 978-3-03835-555-7, ISSN 1013-9826
Anotace:
Bone implants in form of artificial scaffolds manufactured from poly-lactic acid (PLA) represent an attractive alternative to traditional surgical treatments of defective bones (i.e. autografts and allografts). In this work factors influencing biocompatibility and primary stability of implants manufactured from PLA using direct 3D printing were assessed using nanoindentation. For this reason bulk sample of the PLA material and a printed object were subjected to nanomechanical measurement. Quasi-static nanoindentation was employed to identify elastic modulus and hardness distribution on surface and within volume of the samples. Moreover mechanical properties along scanning direction and interlayer characteristics were also assessed. Gradients in mechanical properties have been identified within volume of the material, within the printing layers and at contact between individual layers.
DOI:
10.4028/www.scientific.net/KEM.662.138
Typ:
Stať ve sborníku z prestižní konf. (Scopus)

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

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

Autoři:
Hos, J.; Ing. Tomáš Doktor, Ph.D.; Kostelecká, M.; doc. Ing. Daniel Kytýř, Ph.D.
Publikováno:
2015
Anotace:
Tato bakalářská práce se zabývá určováním orientace vláken v krátkovláknových kompozitních materiálech za pomoci analýzy obrazových dat. Orientace vláken velkou měrou ovlivňuje vlastnosti kompozitních materiálů. Zatímco u dlouhovláknových kompozitů může být orientace snadno kontrolována při výrobě, v případě krátkovláknových kompozitů je takováto kontrola velice obtížná. Práce se zabývá vlastnostmi kompozitních materiálů a základní teorií z oblasti zpracování obrazů. Těchto poznatků je následně využito při tvorbě softwarového nástroje pro určení orientace vláken. Vstupem do programu jsou obrazová data pořízená elektronovým mikroskopem, výstupem jsou histogramy četností orientací jednotlivých vláken.
Typ:
Diplomová práce

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

Autoři:
Hos, J.; Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Petráňová, V.
Publikováno:
2014, Proceedings of 13th Youth Symposium on Experimental Solid Mechanics, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 48-51), ISBN 978-80-01-05556-4
Anotace:
This paper deals with calculation of fibre orientation distribution (FOD) in fibre reinforced composite. The calculation was based on image analysis algorithm applied on image acquired by scanning electron microscope. A composite with oriented fibres was selected to be enable calibration of the algorithm by comparison of the obtained results with FOD declared by the manufacturer.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

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

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

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

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

Autoři:
Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Koudelková, V.; Lukeš, J.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Publikováno:
2014, Key Engineering Materials, Zurich, TRANS TECH PUBLICATIONS LTD), p. 186-189), ISBN 978-3-03785-876-9, ISSN 1013-9826
Anotace:
In the case of material parameters required for evaluation of built heritage preservation state, knowledge of the least possible volume of removed sample is essential in order to minimize damage accumulation to the buildings. These requirements lead to determination of representative volume element (RVE) that was in this paper calculated using combination of image and signal processing techniques. Then, a detailed map of material properties was created using nanoindentation to evaluate local characteristics of the material. Furthermore, atomic composition of samples was quantified by energy dispersive spectrometry (EDX) detector for scanning electron microscopy (SEM) device. Presented method based on combination of SEM, EDX and nanoindentation techniques demonstrates possibility of effective testing in the field of historical buildings preservation.
DOI:
10.4028/www.scientific.net/KEM.586.186
Typ:
Stať ve sborníku z prestižní konf.

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:
10.1088/1748-0221/9/05/C05040
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:
10.4028/www.scientific.net/KEM.586.265
Typ:
Stať ve sborníku z prestižní konf.

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

Autoři:
Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Petr Koudelka, Ph.D.
Publikováno:
2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)
Anotace:
Presented article is focused on plastic strain distribution assessed by microindentation technique. If the nature of the specimen is unsuitable for radiological inspection destructive sample preparation is inevitable to describe its inner state. Two mutually perpendicular planes in deformed zone were manufactured by electrical discharge machining and polishing. One of the planes was created prior the loading procedure and during the loading the parts were connected by screws. In the perpendicular plane the specimen was cut after the loading. Specimens prepared using this procedure were then subjected to microindentation testing. Each set of indents consisted of approximately 150 Vickers microindents covering area of 0.5 mm2. Images of imprint arrays on the specimens surface were acquired by scanning electron microscope. Diagonals of indents were determined and then Vickers hardness values were calculated. Map of hardness distribution was created using cubic interpolation method.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
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:
10.1088/1748-0221/8/02/C02041
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:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Tomáš Fíla, Ph.D.; Ing. Petr Koudelka, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2013, Proceedings of the Fourteenth International Conference on Civil, Structural and Environmental Engineering Computing, Stirling, Civil-Comp Press Ltd), ISBN 978-1-905088-57-7, ISSN 1759-3433
Anotace:
This paper describes the determination of the elasto-plastic properties of base material of aluminium foam Alporas. Three point bending experiments at the micro-scale level in conjunction with inverse finite element simulation were performed. In the cellular structure cell-walls with planar shape were identified and vicinity of such walls was extracted. Harvestedmaterial was embedded into transparent rosin to avoid plastic deformation during the manipulation and the selected wall was extracted. The specimens were finalized by grinding and polishing to achieve approximately rectangular shape. Three projections were acquired using a scanning electron microscope (SEM) and a volumetric model of the samples was developed using a semiautomatic image processing tool. Amicro-scale three-point bending test of semi-prismatic specimens extracted from the cell-wall was performed using a custom designed loading device. Loading was provided using a preloaded lead screw with precise travel. Applied force was measured using a high-accuracy load cell with a loading capacity of 2.25N. Strains were measured optically using the digital image correlation method. The volumetric model developed from the set of SEM projections was discretised using tetrahedral elements with quadratic shape functions. In the simulated bending test the elasto-plastic material model with the von Misses yield criterion and bilinear isotropic hardening was used. Boundary conditions consistent with the experimental oneswere prescribed in the simulation. Themeasured force was sampled at 50Hz and applied to the finite elementmodel. Based on themeasured displacements, parameters of the material model were varied to obtain a best fit to the experimental data (load- deflection curve). Elastic and plasticmaterial constants of the constitutivemodel were identified: (i) Young’smodulus of elasticity, (ii) yield stress and (iii) tangentmodulus.
DOI:
10.4203/ccp.102.104
Typ:
Stať ve sborníku z mezinár. konf.

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

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

Autoři:
Ing. Jaroslav Valach, Ph.D.; Žďárský, M.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Šperl, M.
Publikováno:
2012, Chemické listy, 106 (S3), p. 551-554), ISSN 0009-2770
Anotace:
The paper presents enhanced method for study of severe plastic deformation by hardness mapping utilizing portable hardness tester, flatbed scanner and software processing tool. This technique can be advantageous in situations, where crude information is not only sufficient, but also preferred, especially when it concerns testing on-site and on medium to large scale specimens and construction. Validity of the approach is supported by a comparison of hardness mapping results to the results obtained by an independent method based on evaluation of plastic strains from thermograms. It is shown that both methods determined similar shape and the extent of the plastic zone of the studied specimens.
Typ:
Článek v periodiku excerpovaném SCI Expanded

Autoři:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.
Publikováno:
2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 88-91), ISBN 978-1-63439-432-1
Anotace:
This paper deals with development of the volume model of irregular specimens using optical projections. A s equence of 360 projections of the specimen was acquired and processed using a custom set of procedures developed in MatLab environment. The projections were segmented, filtered and smoothed. A semiautomatic procedure was used to calibrate scale of the projections and to remove eccentricity of axis of rotation of the specimen. The volume model was obtained using inverse Radon transform. Additional procedures were developed to o btain cross- section characteristics required for e valuation of corresponding micromechanical test. For verification of the developed procedure volume models of known shaped objects were estimated and compared.
Typ:
Stať ve sborníku z mezinár. konf.

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

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Nela Krčmářová; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Publikováno:
2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 31-34), ISBN 978-80-01-05062-0
Anotace:
This paper deals with evaluation of hardness fields using Vickers indentation device and a semi-automatic software tool for local hardness distribution mapping. Specimens from low carbon pipeline steels were investigated. Dense grids of Vickers imprints were created on the specimens' surface. Image data of the surface were acquired by a high resolution flatbed scanner with resolution 6400dpi. The imprints were measured using an custom-developed image processing tool, and from the obtained geometrical characteristics local hardness values were derived. From the local hardness values and their coordinates the hardness field in the whole specimen was interpolated.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

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

Autoři:
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. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.
Publikováno:
2011, Engineering Mechanics 2011, Praha, Ústav termomechaniky AV ČR), p. 355-358), ISBN 978-80-87012-33-8
Anotace:
Changes of mechanical properties, namely of modulus of elasticity, often play a role of damage accumulation indicators in the framework of fatigue behaviour of composite materials. In order to improve the reliability of these indicators for identification of material degradation process it is necessary to eliminate the influence of external loading and volume forces associated with thermal expansion of heterogeneous material at various temperatures. Therefore the paper deals with description of experimental assessment of relation between external load and material stiffness and also studies the dependency of material stiffness on temperature. For the monitoring of degradation process ultrasonic measurement was used. Obtained results are discussed with respect to fatigue testing of material and also interpreted from the micromechanical point of view.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

Autoři:
Ing. Tomáš Doktor, Ph.D.
Publikováno:
2011
Anotace:
The paper deals with development of a software tool for assessment of pore size distribution of porous materials. Six types of materials were tested: lime mortars, frit glass, polyurethane foam, polyvinylchloride foam and of human and porcine trabecular bone. Process of preparation of samples is described in order to achieve suitable specimen for image acquisition. For the acquisition of 2D image data four methods were used: CCD camera, scanning electron microscope, laser confocal microscope and high resolution flatbed scanner. The procedure consists of image segmentation, connected component analysis and stereological calculation. A series of mercury intrusion porosimetry measurements was performed and the results were compared with the results of image analysis. Comparison of both groups of results shows a satisfactory agreement. Suitability of developed tool is discussed regarding to type of tested material and to range of pore sizes present in the structure.
Typ:
Diplomová práce

Autoři:
Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Sekyrová, K.; Králík, V.; Němeček, J.
Publikováno:
2011, Chemické listy, 105 (17), p. 729-732), ISSN 0009-2770
Anotace:
The presented paper outlines experimental investigation that is a part of an extensive research plan of study of fatigue properties of aerospace industry grade CRFP laminates. These materials are relatively novel and their long-term behavior and degradation are not yet completely described. Deterioration of this complex material in cyclic loading conditions is to be evaluated by several criteria based on evolution of certain of mechanical properties. Among the criteria is a decrease of modulus of elasticity. In order to reliably detect the changes in this property sensitive three point bending experimental setup was prepared, calibrated and compared to the results of the independent ultrasound method yielding the dynamical modulus of elasticity. Simultaneously, the local mechanical properties were studied by nanoindentation in order to set a reference point for a successive measurement after fatigue tests.
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

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

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.; Kostelecká, M.
Publikováno:
2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 45-46), ISBN 978-1-63439-434-5
Anotace:
This article is focused on assessment of pore size distribution of a porous material. Improvements of the analysis procedure and of the software tools are presented. For the comparison of reliability of the presented method specimena of various origins were tested. As representatives of biological materials specimena of human and porcine trabecular bone were tested, as representatives of artificial materials synthetic pumice and frit glass were used. Images required for the image analysis were captured using a CCD camera, a high resolution flatbed scanner and a confocal microscope. The different methods used to acquire the images are discussed regarding to the range of the pore size, dimensions of the available specimen and properties of the specimen surface. Used image processing algorithms were tested and improved regarding to the variable shape of the voids present in the material structure.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Dudíková, M.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.
Publikováno:
2011, Chemické listy, 105 (S), p. 790-791), ISSN 0009-2770
Anotace:
Article deals with monitoring and optimization of roughness reduction procedure used for preparation of samples for nanoindentation tests. The aim of the research was to measure roughness reduction effect of various combination of grindstones, polishing time, pressure and speed. Suitable procedure with respect to time and cost for three different materials was proposed. For porous materials trabecular bone was chosen, fibre composite as and asbestos-free plates compact ones. Roughness measurement was performed by contactless method using a confocal microscope. Number of grinding steps was reduced and optimal forces and times of grinding were estimated.
Typ:
Článek v periodiku excerpovaném SCI Expanded

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

Autoři:
Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Jiroušek, O.
Publikováno:
2011, Engineering Mechanics 2011, Praha, Ústav termomechaniky AV ČR), p. 115-118), ISBN 978-80-87012-33-8
Anotace:
This paper deals with pore size distribution assessment of trabecular structure of human proximal femur. Two distinct methods for estimation of the pore size distribution histograms are tested, mercury intrusion porosimetry and image analysis. For the image analysis two-dimensional images of crosssections of the specimens were used and the pore size distribution was estimated using a stereological calculation method based on the geometrical properties of an idealized pore. Comparison of the results of both methods is presented. Suitability of both methods for biological materials is discussed regarding to mechanical properties of these materials, characteristics of pores and range of pore sizes present in the structure.
Typ:
Stať ve sborníku z mezinár. konf. cizojazyčně

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

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

Autoři:
Kostelecká, M.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Publikováno:
2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 61-62), ISBN 978-1-63439-434-5
Anotace:
Results from series of tests carried out on nine mixture formulas are the main data set. Asbestos-free plates bonded by hydro-silicate matrix and reinforced by organic fibers were produced from these mixture formulas. Within the scope of this project, the following activities were carried out: finding out the dimensional and weight characteristics of the plates, bending strength under normal conditions, the influence of frost on bending strength, the influence of putting the plates into hot water on bending strength, the impermeability of plates and measurement of change of length in the direction along and across the fibers.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Ing. Tomáš Doktor, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jaroslav Valach, Ph.D.; Jiroušek, O.
Publikováno:
2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 155-157), ISBN 978-88-95940-30-4
Anotace:
Article deals with pore size distribution assessment of porous materials using image analysis. Test samples used in the study were prepared from metal foams and porcine trabecular bone. Two- and threedimensional images were obtained by SEM (scanning electron microscopy) and a high resolution flatbed scanner. For the pore size distribution assessment various methods were used, depending on input data properties (method of obtainig image data) and on pores characteristics (different approach should be used for closed or opened pores). For pore size evaluation using 2D images 25F Association method [5] was used. For verification of the developed algorithms MIP (mercury intrusion porosimetry) measurements were performed, but only in case of trabecular bone samples, because opened pores are necessary for these measurements. Presented algorithms were verified using artificial data structures.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Jiroušek, O.; Zlámal, P.; Pokorný, D.
Publikováno:
2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 151-154), ISBN 978-88-95940-30-4
Anotace:
The quality of bonding between the acetabular cup and pelvis bone plays a key role in total hip replacement stability. One of the source of potential loss of the primary stability is the cement layer degradation. The aim of the research was to investigate the cemented bone-implant interface behavior. The main problems (cement layer degradation and bone-cement interface debonding) during physiological loading conditions have been investigated using a custom hip simulator. The experimental setup was designed to allow cyclic loading of the sample of pelvic bone with implanted cemented acetabular component. The process of damage accumulation in cement fixation was monitored by repeated scanning using high resolution micro Computed Tomography. Use of microfocus source and large high resolution flat panel detector allows investigation of structural changes as well as development of full-scale micro-structural models.
Typ:
Stať ve sborníku z mezinár. konf.

Autoři:
Jiroušek, O.; prof. Ing. Josef Jíra, CSc.; Hrdlička, O.; Kunecký, J.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Jan Vyčichl, Ph.D.; Ing. Tomáš Doktor, Ph.D.
Publikováno:
2010, Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 224 (4), p. 259-267), ISSN 0954-4097
Anotace:
This article deals with finite-element (FE) modelling of the reinforcing effect of the geosynthetic material used in the construction of a ballasted track. Various different designs of geosynthetic material are studied and their reinforcing effects are evaluated in terms of the total settlement reduction. Three-dimensional FE models of the reinforced railway superstructure are compared to a reference FE model with no reinforcement. Each geosynthetic material is modelled respecting its material properties, and the interaction with the ballast material is simulated according to its primary function.
DOI:
10.1243/09544097JRRT319
Typ:
Článek v periodiku excerpovaném SCI Expanded