Characterization of a thermoplastic foam material with the two-layer viscoplastic model

Abstract

This article presents the mechanical characterization of a particular thermoplastic foam material applied in thermoforming processes. During the thermoforming process such materials undergo large deformations, which shows elastic, viscous and yielding properties as well. Additionally, the material behavior is strongly temperature-dependent. The only available material model implemented in the commercial finite element software ABAQUS, which can describe such material behavior properly, is the so-called “two-layer viscoplastic model”. This model is comprised of an elastic-plastic network in parallel with a Maxwell-type viscoelastic branch characterized by a nonlinear dashpot. In our investigations mechanical tests have been performed on several temperatures and based on the experimental results, the material parameters have been fitted using the external optimization software ISIGHT, since the analytical stress-solution for the two-layer viscoplastic model is not available.