Modeling of the Rate Responsive Behavior of Elastomer Foam Materials

Elastomer foam materials are shock absorbers that have been extensively used in applications of electronic packaging. Finite element modeling simulation plays an important role in helping the designers determine the best elastomer foam material and the best structure of a shock absorber. Elastomer foam materials have very complicated material behaviors. The prediction of the rate responsive behavior is one of the most interesting topics in elastomer material modeling. The focus of this article is to present a unique method for deriving the rate dependent constitutive model of an elastomer foam based on the extension of the Cowper and Symond law and the curve fitting on experimental test data. The research on rate dependent material models and the material models available in commercially available finite element analysis software have been reviewed. Test data collection at various strain rates has been discussed. Two steps of curve fitting on experimental test data are used to retrieve analytical expression of the constitutive model. The performance of the constitutive model for a foam material has been illustrated and shown to be quite good. This method is easy to understand and the simple formulation of the constitutive model is very suitable for applications in numerical simulation. The constitutive model could be used to predict the stress-strain curves of a foam material at any strain rate, especially at the intermediate strain rates, which are the most difficult to collect so far. In addition, this model could be readily integrated with the hyperelastic material models to more efficiently evaluate the mechanical behavior of an elastomer foam material. The model could potentially be implemented in commercially available software such as ABAQUS and LS-DYNA. The method presented is also useful in deriving constitutive models of rubberlike elastomer materials.