The influence of preliminary rolling on the mechanical properties of polyethylene terephthalate

The influence of preliminary rolling on the mechanical behavior of amorphous polyethylene terephthalate (PET) has been studied. Samples were oriented via rolling at room temperature on laboratoryscale rolls. After low rolling degrees (lambda = 1.15), the tensile yield point decreases; i.e., the effect of strain softening is observed. With time, the yield point recovers gradually, a behavior that is similar to that of polystyrene described in the literature. Rolling suppresses the tendency of polyethylene terephthalate to brittle fracture. This result is due to the decrease in the degree of inhomogeneity of deformation in the neck. At rolling degree lambda = 2 necking is completely suppressed. The dependence of the true yield stress of polyethylene terephthalate on the degree of orientation has been obtained. It has been shown that the Konsider diagram describes not the stress of the transition from neck propagation to homogeneous deformation but the degree of orientation at which necking ceases.