A Viscoplastic Constitutive Model for Polyurethane Foams

Abstract

A series of experiments was recently performed to characterize the mechanical response of several different rigid polyurethane foams to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Based on these experiments, a foam plasticity model that captures volumetric and deviatoric plasticity was developed. This model has a yield surface that is an ellipsoid about the hydrostat. These polymeric foams were also found to be very strain-rate and temperature dependent. Thus, a new viscoplastic foam model was developed to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This paper includes a description of recent experiments and experimental findings. Next, development of a foam plasticity model and a viscoplastic foam model is described. Finite element simulations with the new models are compared with experimental results to show behavior that can and cannot be captured with these models.