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Keywords: nanoindentation, micro-CT, constitutive equations, finite element modelling, trabecular bone.

Summary

This paper deals with utilization of finite element models of microstructure of complex materials with material properties obtained from nanoindentation to assess the overall material properties. As an example of such material, a sample of trabecular bone is taken. Material properties at the trabecular level are obtained from nanoindentation. Parameters for the material models are obtained by fitting the experimental force-displacement curve with response obtained from the finite element simulation of the nanoindentation solved as an axisymmetric problem. Two different plasticity criteria are compared in the study. The material model is used in further finite element analysis taking the microstructure into account. The finite element model of the structure is developed from the series of micro-CT scans using either voxel or tetrahedral elements. The finite element models are subjected to compressive loading in three principal directions and effective elastic properties and effective yield stresses are computed. The computed elastic modulae are compared to values measured using the same specimen and standard compressive tests in the elastic region. The microstructural finite element models can easily be used to calculate the orthotropic elastic properties and also to calculate the overall yield stress. This enables for quick comparison of the material properties of different samples, e.g. to study the influence of the osteoporotic changes in the microstructure (trabecular thinning) on the material properties and that for example increase the risk of osteoporotic fracture for the cases studied. Overall, the described procedures are promising for detailed analysis of the deformation behaviour of materials with complex inner structure, e.g. trabecular bone. The results obtained using finite element modelling indicate a great importance of the quality of tetrahedral elements, need for second-order elements and proper surface detection when converting the µCT data into a surface mesh. In both voxel and tetrahedral meshes the strain distribution is very localized imposing special requirements on the mesh quality. These high-resolution microstructural finite element models can be used to study the mechanical behavior of bone under complex loading or to study the effects of microstructural changes on the overall mechanical performance.

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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	Civil-Comp Proceedings ISSN 1759-3433 CCP: 91 PROCEEDINGS OF THE TWELFTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping, L.F. Costa Neves and R.C. Barros Paper 141 Combining Nanoindentation and Real-Time Tomography for Micro Finite Element Models of Materials with Complex Inner Structure O. Jirousek¹, J. Nemecek² and P. Zlamal³ ¹Institute of Theoretical and Applied Mechanics AS CR, v.v.i, Czech Republic ²Faculty of Civil Engineering, CTU in Prague, Czech Republic ³Faculty of Transportation Sciences, CTU in Prague, Czech Republic doi:10.4203/ccp.91.141 purchase the full-text of this paper Full Bibliographic Reference for this paper O. Jirousek, J. Nemecek, P. Zlamal, "Combining Nanoindentation and Real-Time Tomography for Micro Finite Element Models of Materials with Complex Inner Structure", in B.H.V. Topping, L.F. Costa Neves, R.C. Barros, (Editors), "Proceedings of the Twelfth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 141, 2009. doi:10.4203/ccp.91.141 Keywords: nanoindentation, micro-CT, constitutive equations, finite element modelling, trabecular bone. Summary This paper deals with utilization of finite element models of microstructure of complex materials with material properties obtained from nanoindentation to assess the overall material properties. As an example of such material, a sample of trabecular bone is taken. Material properties at the trabecular level are obtained from nanoindentation. Parameters for the material models are obtained by fitting the experimental force-displacement curve with response obtained from the finite element simulation of the nanoindentation solved as an axisymmetric problem. Two different plasticity criteria are compared in the study. The material model is used in further finite element analysis taking the microstructure into account. The finite element model of the structure is developed from the series of micro-CT scans using either voxel or tetrahedral elements. The finite element models are subjected to compressive loading in three principal directions and effective elastic properties and effective yield stresses are computed. The computed elastic modulae are compared to values measured using the same specimen and standard compressive tests in the elastic region. The microstructural finite element models can easily be used to calculate the orthotropic elastic properties and also to calculate the overall yield stress. This enables for quick comparison of the material properties of different samples, e.g. to study the influence of the osteoporotic changes in the microstructure (trabecular thinning) on the material properties and that for example increase the risk of osteoporotic fracture for the cases studied. Overall, the described procedures are promising for detailed analysis of the deformation behaviour of materials with complex inner structure, e.g. trabecular bone. The results obtained using finite element modelling indicate a great importance of the quality of tetrahedral elements, need for second-order elements and proper surface detection when converting the µCT data into a surface mesh. In both voxel and tetrahedral meshes the strain distribution is very localized imposing special requirements on the mesh quality. These high-resolution microstructural finite element models can be used to study the mechanical behavior of bone under complex loading or to study the effects of microstructural changes on the overall mechanical performance. purchase the full-text of this paper (price £20) go to the previous paper go to the next paper return to the table of contents return to the book description purchase this book (price £140 +P&P)
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