Large Deformations of Semicrystalline Polymer Modeled Using the Necking Network Concept

Previously, a physically-based elastic model has been used in the modeling of high temperature polymer deformation. While this has been successful in producing realistic shapes and forces in necking polymers, the elastic nature of the theory causes some discrepancies between the predictions and the experimental observations. The theory does not describe the observed rate dependence of drawing forces, and at some stages of deformation the predicted inhomogeneity is greater than is observed. The latter effect is the result of the elastic theory’s ability to change instantaneously from a homogeneous to an inhomogeneous state of strain, corresponding to the development of a neck. In this paper, we model the development of necks in tensile specimens using an extension of the model in which rate dependence has been incorporated in a simple way. The incorporation of rate dependence results in a model of neck development in which the changes in strain are less abrupt and the predicted shapes more realistic. To evaluate the model, specimens of polypropylene were stretched at 150°C and their images captured and analysed digitally. Predictions of the shapes were generated by incorporating the model into the finite element package ABAQUS.