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D. H. Pahr, H. J. Böhm:
"Assessment of Mixed Uniform Boundary Conditions for Predicting the Macroscopic Mechanical Behavior of Composite Materials";
Vortrag: ECCM 13 - 13th European Conference on Composite Materials, Stockholm; 02.06.2008 - 05.06.2008; in: "Proceedings of ECCM 13", (2008), Paper-Nr. 1216, 10 S.

inite Element models can be used to study the macroscopic mechanical properties of inhomogeneous materials in more detail than experiments. Appropriate boundary conditions have to be applied to volume elements (VE) and apparent instead of effective overall elastic properties are usually computed. Typical BCs used in such works are kinematic uniform (KUBC), static uniform (SUBC), and periodic boundary (PBC) conditions. Less well known are uniform displacement-traction (orthogonal mixed) BCs (MUBC). Special MUBCs were recently proposed by Pahr and Zysset. This set of mixed BCs was found to be an excellent choice for extracting the full apparent elasticity tensors of nearly orthotropic cellular materials. Simulations of periodic and microscopically orthotropic volume elements give exactly the same overall elastic properties as those obtained by periodic BCs. Therefore, they are called periodic compatible MUBC (PMUBC). The advantage of PMUBCs is that they can be used for non-periodic inhomogeneous media at lower numerical costs and less modelling effort as periodic BCs. But in this case they provide only apparent overall properties. The objective of this study is to show how mixed uniform BCs work. Furthermore, existing volume elements describing particle and short fiber reinforced composites, trabecular bone, a biological cellular material, and a woven fabric laminate are investigated in the linear elastic regime using PMUBCs, PBCs, as well as KUBCs. In that way apparent and effective predictions for the macroscopic elastic tensors are obtained and can be compared in order to assess the accuracy of PMUBCs. In addition, some elastoplastic load cases involving PMUBCs and PBCs are studied.