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

Uniaxial deformation of amorphous thick and massive poly(ethylene terephtha late) ( PET) samples above the glass transition temperature has been studie d 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, ma ke it possible to determine true stress nn true strain data at constant tru e strain rate up to very high strains of similar to2.5. The mechanical resp onse of PET in these conditions is modelled as a molecular network exhibiti ng a rubberlike behaviour. Sufficiently far from the alpha transition, it i s shown that the Edwards and Vilgis model is able to reproduce experimental data accurately, which also offers a relevant insight into the nature of t he molecular networks. Closer to the alpha transition, this purely hyperela stic model needs refining and improving to take into account an additional non-elastic contribution.