|
| |
|
|
On the modelling of compressive response of closed-cell aluminium foams under high-strain rate loading
Koudelka_ml., P. ; Zlámal, Petr ; Fíla, Tomáš
Porous metals and particularly aluminium foams are attractive materials for crash applications where constructional elements have to be able to absorb considerable amount of deformation energy while having as low weight as possible. Compressive behaviour for medium impact velocities can be experimentally assessed from a series of droptower impact tests instrumented with accelerometer and high-speed camera. However to predict such behaviour a proper modelling scheme has to be developed. In this paper droptower impact tests of Alporas aluminium foam were used for development of a material model for explicit finite element simulations of high-strain rate deformation process using LS-DYNA simulation environment. From the material models available low density foam, Fu-Chang’s foam, crushable foam and modified crushable foam models were selected for simulations using smoothed-particle hydrodynamics and solid formulations respectively. Numerical simulations were performed in order to assess constitutive parameters of these models and identify material model describing deformation behaviour of Alporas with the best accuracy.
|
|
|
Proceedings of 13th Youth symposium on experimental solid mechanics
Kytýř, Daniel ; Zlámal, Petr ; Růžička, M.
Proceedings of the 13th Youth Symposium on Experimental Solid Mechanics held in Decin, Czech Republic. The symposium is focused on experimental methods and numerical simulation in engineering sciences. The proceedings capture the trends in development of experimental methods in mechanics of structures and materials (regardless to the material and structure type, covering fields from civil and mechanical engineering to biomechanics) as well as deployment of particular solution for measurement and automation systems for evaluation of experimental data.
|
|
|
Experimental study on size effect in quasi-static compressive behavior of closed-cell aluminium foams
Koudelka_ml., Petr ; Zlámal, Petr ; Kytýř, Daniel ; Fíla, Tomáš ; Jiroušek, Ondřej
The size effect in compressive deformation behaviour of commercially available aluminium closed-cell foam Alporas was studied under quasi-static loading conditions with different boundary conditions. Dimensions of the specimen’s cross-section were selected to match those of sufficient representative volume element (RVE) obtained by spectral analysis of the macroscopic structure whereas different heights of specimens were tested to examine size-scaling factor. Mechanical properties were derived from three different data sources: I) using data captured by load-cell, II) by digital image correlation (DIC) of displacement of contact faces, III) by DIC of the specimen’s structure. Mechanical testing was performed in custom-built loading device as well as in Instron 4301 electromechanical testing system with custom computer control software.
|
|
|
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.
|
|
|
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.
|
|
|
On the reliability of microstructural models of trabecular bone with tissue properties from nanoindentation for bone quality assessment
Jiroušek, Ondřej ; Zlámal, Petr
Material properties of trabecular bone can be inversely determined by microstructural finite element (FE) models. The geometry of these models is developed using three-dimensional image data from microfocus Computed Tomography (micro-CT). The reliability of these models to predict the overall elastic properties is influenced by several factor, namely the tissue material properties, resolution of the input images, quality of the segmentation and quality of the FE mesh. This article describes all the aspects of proper and reliable inverse estimation of bone quality using the microstructural models with tissue properties assessed by nanoindentation.
|
|
|
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.
|
host ::
RSS.