Characterisation and modelling of anisotropic thermo-mechanical behaviour of oriented polyethylene terephthalate

The long-term and short-term anisotropic mechanical behaviour of a biaxially stretched polyethylene terephthalate foil is measured. The orientation of the crystalline phase is characterized and the representative foil microstructure is discussed. Using the obtained information, a mean-field model is used to simulate the elasto-viscoplastic behaviour of the oriented polymer foil, taking into account the different constitutive behaviour of the phases. The material is modelled as an aggregate of connected two-phase domains. The parameters of the constitutive behaviour of the crystalline and non-crystalline phases have been determined, and the ability to simulate the large-strain anisotropic behaviour of polyethylene terephthalate in the strain-rate-controlled regime and the long-term creep has been demonstrated. The model is extended to include pre-orientation of the non-crystalline phase. In addition, deformation at the microscopic level is analysed using the model results.