Experimental and theoretical study of uniaxial deformation of amorphous poly(ethyleneterephthalate) above glass transition temperature

Uniaxial deformation of amorphous thick and massive poly(ethylene terephthalate) (PET) samples above the glass transition temperature has been studied in the temperature range relevant to the stretch-blow moulding process of PET bottles. A video controlled system coupled to a novel clamping device, together with accurate control of the thermal gradient in the material. make it possible to determine true stress v. true strain data at constant true strain rate up to very high strains of -2-5. The mechanical response of PET in these conditions is modelled as a molecular network exhibiting a rubberlike behaviour. Sufficiently far from the alpha transition, it is shown that the Edwards and Vilgis model is able to reproduce experimental data accurately, which also offers a relevant insight into the nature of the molecular networks. Closer to the alpha transition, this purely hyperelastic model needs refining and improving to take into account an additional non-elastic contribution.