Material modelling considering the pressure dependence and the volume change for plastics with applications to the interior parts of a vehicle

The nature of the contact between the occupants and the interior structure of a vehicle following a collision is the primary cause of injury in car accidents. The interior parts of vehicles are typically made from various kinds of plastic. The deformation and failure of these materials largely determine the injury risk to the occupants. Among the various materials used to fabricate the interior parts of vehicles, plastics exhibit softening, dilatational, pressure-dependent and anisotropic characteristics, which should be considered in the design of the interior parts of those vehicles. However, it is difficult to describe the mechanical behaviour of plastics because classical models (e.g. the piecewise-linear plasticity model) using the isotropic yield criterion and the hardening rule are typically applied. Therefore, the objective of this study was to advance the numerical modelling technique for the interior materials of a vehicle and to suggest the test process for obtaining the material parameters. This paper compares the various material models that can be applied to plastics and describes a phenomenological model that includes a variable Poisson’s ratio, damage and stress–strain characteristics which are dependent on the rate of change in the applied load. Several tests were carried out to evaluate the mechanical characteristics of plastics and to obtain the parameters of the phenomenological material model. Free-motion headform impact in a pillar trim was analysed to compare the differences between the classical model and the phenomenological model.