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Modelling of Foams using MAT83 – Preparation and Evaluation of Experimental Data

Enver Serifi, Universität Stuttgart Andreas Hirth, DaimlerChrysler AG Stefan Matthaei, DaimlerChrysler AG Heiner Müllerschön, DYNAmore GmbH Foam materials are widely used in automotive industry such as energy absorbers and comfort enhancers. Because of high energy absorbing capability of foams, they became very important in vehicle crashworthiness. So in this manner, FE modelling of foam materials also becomes important. Although foam materials are very promising materials, not that much study has been done about foams comparing to other commonly used materials like steel, etc. Some different approaches are available to define the behaviour of foam materials. One micro-structural approach to define the mechanical behaviour of foam materials, considers the foam material as a cubic model and uses the standard beam theories with solid-fluid interaction to describe the in- and out-flow of fluid inside the foam material (see Gibson and Ashby [1]). There are also macro-structural approaches those consider the foam material as a continuum with solid-fluid interaction in order to describe the in- and out-flow of the pore-fluid in the foam material (e.g. Ehlers [2]). In contrast to such quite sophisticated models, in LS-DYNA for practical engineering purposes the foam model *MAT_FU_CHANG_FOAM (MAT83) is available. The main assumption of MAT83 is, that Poisson’s ratio is equal to zero for foams and therefore no coupling between the material axes is present. This leads to a one-dimensional material law, where experimental curves of uni-axial test can be used directly. The aim of this work is to provide a method and to develop a computer program in order to generate reliable input data for the simulation of EPP foam with MAT83 in LS-DYNA. Experimental raw data have to be prepared and extended respectively. In addition, suitable density laws have to be developed in order to provide LS-DYNA input data for intermediate densities, where no experimental data are available. To verify the reliability of the results, simulations with the generated curves are compared to an independent experimental database and to some real experimental applications.