Constitutive Equation for Plastic Behavior of Hydrostatic-Pressure-Dependent Polymers

Abstract

Hydrostatic pressure dependence of the mechanical behavior of polymers is studied, using constitutive modeling of the yield surface described by the first and the second invariants of stress and the nonassociated flow rule that satisfies the incompressible hypothesis. An internal variable theory of rate-independent plasticity is presented, which incorporates isotropic hardening as a function of accumulated plastic strain. After the determination of material constants under uniaxial tension and compression, the model shows that the von Mises-type effective stress - plastic strain curves under multiaxial load are quite different from those under uniaxial load. The model is compared with the experimental results of uniaxial tension and compression obtained by Spitzig and Richmond and those of torsion obtained by Silano et al. under high pressure.