Numerical analysis of neck propagation in polymeric materials. Part 2 – Neck propagation behaviour of poly (butylene terephthalate) mouldings

Abstract

This paper examines the factors controlling the formation and propagation of a neck in poly (butylene terephthalate) (PBT) mouldings under tensile loading. Tensile tests were used to investigate the load–displacement and deformation behaviour of PBT and the accompanying changes in surface temperature. In parallel with this experimental study, a numerical model was developed for the deformation of PBT mouldings and neck formation under tensile loading analysed using finite element analysis (FEA). The calculated numerical results were compared with the experimental data. This work has shown that formation does not occur in PBT immediately after the yield point. Instead, plastic deformation first progresses homogeneously through the testpiece. Neck formation and propagation, accompanied by a rise in temperature, then follow. The load–displacement behaviour calculated using FEA could be approximated to the experimental data by adapting an elastic–plastic model at a stable temperature to the necking behaviour of PBT moulding. Furthermore, the dependence of neck formation on strain rate is related to the plastic instability, as demonstrated by the numerical results, and does not depend upon heating effects.