DETERMINATION OF THE TRUE STRESS-STRAIN BEHAVIOR OF POLYPROPYLENE

The true tensile and compressive stress-strain curves for a typical se micrystalline polymer (polypropylene) were constructed with a new expe rimental technique. This is based on a non-contact method of strain me asurement along the specimen gauge length. The viscoplastic behaviour obtained in this manner was then described with a nonlinear viscoelast ic constitutive model mentioned analytically elsewhere. This considera tion leads to a satisfactory description of yield and post yield behav iour, including strain softening, and strain hardening. The rate effec t was also predicted with a high accuracy.