Material Characterization of Polymers Using CAE and Correlation with Tests

Progress in material research is the driving force behind innovative ideas and characterising the newly invented material accurately is need of the hour. Increased use of polymers in automobile industry has led to the need for accurately capturing polymer material properties. In case of polymers, we generally observe negative slope in true stress strain curves due to inherent material behaviour. It is mainly because of polymer chains which realign/untangle in the direction of load. This is a challenge when we characterise polymers material properties to be used in LS_DYNA software, which is widely used in automotive applications to solve dynamic crash events. This software does not allow negative slope in stress strain curves in the plastic region and that causes model instabilities. This paper explains the methodology to avoid negative slope and still characterise the polymers without significantly loosing on the accuracy and correlation to physical tests. *MAT24 (PIECEWISE LINEAR ELASTICITY) is the most common and simple material model used to represent the polymer in LS DYNA. As these polymer materials are used further for crash simulations, it is characterised at different strain rates including quasi static and higher strain rates. Different physical tests like tensile test and DynaTup test are carried out to find the polymer material properties. As a part of this study, CAE results are correlated with the physical test results to validate material. Results are sensitive to mesh size in Finite Element Methods. The paper talks about trend of mechanical properties with respect to mesh size, temperature and different strain rates.