Nonlinear constitutive equation for polyethylene under combined tension and torsion

In order to investigate a viscoelastic‐plastic nonlinear constitutive equation for polymer solids, combined tension and torsion tests were performed using polyethylene (PE) hollow cylinders. The experimental data were compared with the numerical results derived from a multiaxial constitutive equation developed from the uniaxial one proposed by Krempl. It is shown that the proposed theory fairly well describes the stress–strain curves of PE up to relatively high strain ranges not only in simple torsion, but also under combined tension–torsion, provided that the current strain is not below the maximum previous strain.