NONLINEAR CONSTITUTIVE EQUATION OF POLYPROPYLENE UNDER COMBINED TENSION AND TORSION

Combined tension and torsion tests were performed at various strain histories using polypropylene (PP) hollow cylinders. The experimental stress-strain curves were compared with the multiaxial constitutive equation which is extended from the uniaxial one based on the overstress concept of Krempl. It is shown that the theory agrees with the experimental curves under pure torsion as well as combined tension-torsion, provided that the current strain is not below the maximum strain. © 1990 Chapman and Hall Ltd.