|
|
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.
|
|
|
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.
|
|
|
Large-scale micro-finite element simulation of compressive behavior of trabecular bone microstructure
Jiroušek, Ondřej ; Zlámal, Petr
Microstructural finite element analysis has become a standard technique for evaluation of mechanical properties of trabecular bone. Due to the high complexity of the trabecular bone microstructure, the FE models have a very large number of elements (about 1 million elements per cubic cm in 50 μm3 resolution). To perform FE analysis of the microstructural FE models based on micro-CT scanning of whole bone samples (e.g. vertebral bodies) it is needed to solve 107 -- 108 equations. This article deals with comparison of approaches using voxel-based microstructural FE models to calculate the overall mechanical properties of trabecular bone.
|
|
| |
|
| |
|
|
Microstructural models of trabecular bone - comparison of CT-based FE models
Jiroušek, Ondřej ; Zlámal, Petr
In the article a detailed comparison of techniques used to developed detailed FE models of trabeculra bone microstructure is presented. The FE models are built using a stack of microtomographic images of trabecular bone. Compression test of a cylindrical sample taken from human proximal femur is virtually performed using FE models developed using different procedures. Effect of improper segmentation, mesh smoothing, mesh density, use of hexahedral/ tetrahedral elements, linear/ quadratic shape function is evaluated in parametric study. Material model is based on nanoindentation and numerical elastic properties of sample are compared to experimental results.
|
|
|
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.
|
|
|
Kalibrace konstitutivního modelu trabekulární kosti na základě nanoindentace
Zlámal, Petr ; Jiroušek, Ondřej ; Němeček, J.
The paper deals with investigation of a trabecular bone behaviour during nanoindentation test. Behavior of trabecular bone is investigated using real nanoindentation and finite element simulation. Two different plasticity criteria for material model of trabeculae are tested, namely von Mises and Drucker-Prager. Von Mises criterium is extended bilinear isotropic hardening. Constants needed for numerical material model are obtained from fitting procedure of a experimetal load-displacement curve.
|
|
| |
|
|
Bezpečnost elektronického bankovnictví v České republice
Nečas, Marek ; Dvořáček, Jiří (advisor) ; Zlámal, Petr (referee)
Bezpečnost elektronického bankovnictví vždy byla, je a bude důležitým faktorem, který má vliv na chování uživatelů i finančních institucí. Bezpečnosti je potřeba neustále se věnovat, sledovat možné hrozby, ale i nové příležitosti. Banky by měly nabízet moderní způsoby zabezpečení a mít fungující bezpečostní politiku. Klienti by měli mít jistotu, že jejich finanční úspory jsou v bezpečí. K tomu by měli využívat modernější a bezpečnější technologie.
|
guest ::
RSS feed.