Chapter 6 – Finite element modelling of foam deformation

Finite Element Analysis (FEA) is used to find the stress distribution for complex geometries. This chapter explores the background to foam material models in FEA. Hyperelastic FEA models for flexible foams, with parameters that describe a range of test data types, can be used to analyze complex strain fields such as those in indentation tests. ABAQUS provides detailed explanations of the foam models. To model hysteresis or rate-dependent behavior, viscoelastic behavior can be associated with a hyperelastic model in ABAQUS Explicit. The response of the crushable foam model in ABAQUS differs from that of low-density extruded polystyrene (XPS), especially when the foam is unloaded, or during shear or tensile deformation. The foam acts as if an elastic volumetric hardening mechanism is in parallel with a plasticity mechanism. The foams are softer in unloading than loading, because cell faces have formed plastic hinges during compressive loading. FEA predictions are approximations because many rigid foams are slightly anisotropic, while FEA is for isotropic materials; the crushable foam model has the same hardening in uniaxial and hydrostatic compression. New material models will combine the behavior of hyperelastic foams and crushable rigid foams.