An Anisotropic Visco-hyperelastic model for PET Behavior under ISBM Process Conditions

The mechanical behavior of Polyethylene Terephthalate (PET) under the severe loading conditions of the injection stretch blow molding (ISBM) process is strongly dependent on strain rate, strain and temperature. In this process, the PET near the glass transition temperature (Tg) shows a strongly non linear elastic and viscous behavior. In author's previous works, a non linear visco-hyperelastic model has been identified from equi-biaxial tensile experimental results. Despite the good agreement with biaxial test results, the model fails to reproduce the sequential biaxial test (with constant width first step) and the shape evolution during the free blowing of preforms. In this work, an anisotropic version of this visco-hyperelastic model is proposed and identified form both equi and constant width results. The new version of our non linear visco-hyperelastic model is then implemented into the Abaqus environment and used to simulate the free blowing process. The comparison with the experimental results managed in Queen's University Belfast validates the approach.