Numerical analysis of neck propagation in polymeric materials. Part 1 – Neck propagation behaviour of poly (ethylene terephthalate) film

Abstract

Neck formation and propagation in poly (ethylene terephthalate) (PET) films have been investigated using finite element analysis (FEA). First, the criteria for the occurrence of neck propagation are examined and a unique constitutive law for polymers is proposed. Neck propagation is associated with a steep rise of the tangent modulus in the plastic deformation region. The ability of the specimen to form a neck is determined by the ratio of the yield stress to the tangent modulus immediately after the yield point. Next, the characteristic load–displacement behaviour in neck formation and propagation is investigated using FEA. Finally, numerical results are compared with experimental data. The calculated values agree with experimental data on load–displacement behaviour, especially for the decrease in load immediately after yield. An apparent constitutive law representing the load–displacement behaviour of PET film has been successfully obtained. By comparing the experimental results with numerical predictions of the neck localisation and propagation process, it is shown that the decrease in load is related to the recovery of deformation in the region outside the neck.