Mechanical behaviour of a semicrystalline polymer before necking

The behaviour of semicrystalline polypropylene (PP) was studied in the pre- necking domain. Mechanical tests were performed to characterize the behavio ur of this multiphase material. Test results have distinctly characterized both its viscoelastic and its viscoplastic behaviour. The usual approach to studying metals was adopted to investigate the effect of heterogeneities c aused by spherulitic morphology. By this macroscopic approach, the macrosco pic stress was split into an effective stress and a back stress so that the interactions between crystalline lamellae and amorphous phases could be ta ken into account. This improved knowledge of the macroscopic mechanical beh aviour was used to develop both viscoelastic and viscoplastic models.