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Indirect determination of material model parameters for single trabecula based on nanoindentation and three-point bending test
Zlámal, P. ; Jiroušek, Ondřej ; Kytýř, Daniel ; Doktor, Tomáš
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.
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Assessment of micromechanical properties of trabecular bone using quantitative backscattered electron microscopy
Kytýř, Daniel ; Petráňová, Veronika ; Jiroušek, Ondřej
The biomechanical behaviour of trabecular bone depends not only on its microarchitecture but also on mineral density distribution. Bone mineral density distribution is coupled with mechanical properties of the tissue. In this preliminary study intratrabecular composition of individual trabeculae was investigated. The quantitative backscattered electron microscopy (qBSE) a method based on detection of electrons backscattered from surface layer of the specimen was employed to obtain high resolution images of the transverse sections of a trabecula. From acquired data the element map was created, organic (collagen fibres) to anorganic (hydroxyapatite) material ratio computed and collagen fibres orientation assessed. To conclude qBSE allows to obtain detail information about intratrabecular composition and material properties at the level of individual trabeculae.
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Early Defect Detection of Acetabular Implants
Kytýř, Daniel ; Jiroušek, Ondřej ; Zlámal, Petr ; Doktor, Tomáš ; Jandejsek, I.
The paper is focused on possibilities of modern X-ray detectors and micro-focus X-ray source for investigation of early degradation processes of acetabular implants. To simulate the most adverse activity (downstairs walking) a hip joint simulator was developed. The experimental setup was designed for cyclic loading of polyethylene acetabular cup implanted into the human pelvic bone and fixed by commercial polymethyl methacrylate bone cement. To predict the bone degradation numerical analysis of detailed three-dimensional model of the acetabular cup and the cement mantle implanted in a bone block was performed. Using large area flat panel detector and microfocus X-ray source it is possible to investigate micro-damage propagation and detect early defect in the bone-implant interface.
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Investigation of C/PPS Composites Degradation Process Using Acoustic Measurement
Fíla, Tomáš ; Valach, Jaroslav ; Kytýř, Daniel ; Šperl, Martin
The article deals with assessment of fatigue degradation of C/PPS composites using simple acoustic measurement technique. Changes in natural frequency and attenuation decrement were chosen as indicators of fatigue damage accumulation in the studied composite material. New testing device was developed for acoustic measurement. The experimental setup was designed to chime the specimen by repeatable force of stiff striker exciting a specific natural mode of vibration and to record the acoustic response of the specimen to the impact simultaneously. From the power spectral density of the signal the natural frequency was obtained. Using the same signal, the attenuation decrement was estimated from regression of the its envelope.
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Pore Size Distribution of Human Trabecular Bone - Comparison of Intrusion Measurements with Image Analysis
Doktor, Tomáš ; Valach, Jaroslav ; Kytýř, Daniel ; Jiroušek, Ondřej
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.
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Assessment of C/PPS composites degradation indicators using acoustic measurement
Kytýř, Daniel ; Valach, Jaroslav ; Doktor, Tomáš ; Jiroušek, Ondřej
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.
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Deformační analýza trabekulární kosti za použití mikrotomografie v čase
Jiroušek, Ondřej ; Zlámal, Petr ; Kytýř, Daniel ; Kroupa, M.
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.
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Zjišťování mikrostrukturálních vlastností acetabula lidské pánve pomocí mikro-CT
Kytýř, Daniel ; Jiroušek, Ondřej ; Vavřík, Daniel
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.
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