Cyclic deformation behaviour and morphology of polypropylene

Abstract

The viscoelastic-plastic behaviour and stress relaxation in polypropylene after uniaxial simple tension or cyclic preloading are studied by an electrohydraulic, servo-controlled testing machine. The stress-strain curve data of simple tension at different strain rates show that the magnitude of stress depends strongly on strain rate. The stress relaxation behaviour after simple tension and cyclic preloading indicates complex features and reveals differences in the deformation of molecular chains in polypropylene subjected to different cyclic preloadings. The stress-strain curves and the stress relaxation curves under three mean strains are fairly different from each other. The microstructural changes in samples subjected to different cyclic preloadings were determined by scanning electron microscopy (SEM). The results of the stress-strain curves and the stress relaxation behaviour are discussed in comparison with the observation of SEM fractographs.