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Comparative study on numerical and analytical assessment of elastic properties of metal foams
Koudelka_ml., Petr ; Jiroušek, Ondřej ; Doktor, Tomáš ; Zlámal, Petr ; Fíla, Tomáš
Recently, titanium metal foams are being considered as a suitable replacement for substituting trabecular bone microstructure especially for their similar pore distribution. The most common methods for determination of compressive effective elastic properties of such materials involve different approaches based on finite element analysis (FEA) of their microstructure. The internal geometry is usually modeled by two different methods - directly on the basis of a series of CT scans or using one of discretization schemes. However, all these techniques require highly specialized hardware, software and significant amount of computational time. In this paper, the effective elastic properties of the metal foam are instead obtained by analytical modulus-porosity relations and results are compared with previous FE based analysis.
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Design and use of novel compression device for microtomography under applied load
Fíla, Tomáš ; Zlámal, Petr ; Koudelka_ml., Petr ; Jiroušek, Ondřej ; Doktor, Tomáš ; Kytýř, Daniel
This paper deals with modification and usage of custom-designed compression device, that allows real time X-ray tomography scanning of specimen under applied pressure. In this case microtomography is used to obtain data required to determine specimens morphology and to develop 3D material model (especially for cellular materials such as bones, metal foams and quasi-brittle materials or particle composites such as concrete or cementitious composites). Important design changes were made in the existing device frame to increase its load capabilities, stiffness and to accomodate a larger specimen. Finally device displacement measurements were conducted and calibration experiment was carried out.
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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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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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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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