Modelling the large strain constitutive behaviour of polycarbonate under isothermal and anisothermal conditions

Abstract

We have studied the tensile behaviour of polycarbonate at large strains below the glass transition temperature. Experiments have been carried out at a series of constant temperatures and also under conditions of falling temperature. The specimens neck with a natural draw ratio of ~2, and the study focuses mainly on the necked material. Isothermal experiments reveal an elastic mechanism that initiates beyond the natural draw ratio. A model consisting of an Eyring process and two Gaussian elastic mechanisms is shown to be applicable to both the isothermal and anisothermal stress relaxation and stress-strain results. The same model also produces reasonable estimates of the stresses generated during the necking process. In addition, a simple relationship between isothermal and anisothermal stress relaxation is demonstrated.