Abstract
Polymeric material is used in fields such as electricity and electronic parts. In this report, deformation behaviors of polypropylene after pre-straing are investigated under biaxial stresses to establish the constitutive model. A series of equi-strain loci after tensile and torsional pre-straings can be expressed numerically for various strain rates in Mises type stress plane by considering hydrostatic pressure effect in flow stress. By using the obtained equations of the equi-strain loci and the normality rule with respect to plastic strain incremental vector, stress paths are calculated at loading along various strain paths with a corner of various angle. It is confirmed that rather good agreement can be obtained between experimental and predicted results on stress-strain curves of Polypropylene in reloading after pre-straings.
