Modification of Isotropic Hardening Model and Application of Kinematic Hardening Model to Constitutive Equation for Plastic Behavior of Hydrostatic-Pressure-Dependent Polymers

摘要

Hydrostatic pressure dependence of the mechanical behavior of polymers is studied by three constitutive modeling, in which the yield surface is described by the first and the second invariant of stress and the nonassociated flow rule satisfies the incompressible hypothesis. An internal variable theory of rate-independent plasticity is presented, which incorporates isotropic hardening and kinematic hardening. Both evolution equations of isotropic hardening variable and hydrostatic-pressure-dependent variable are formulated and the previous model is modified. The predicted results of the model are compared with the experimental ones of uniaxial tension and compression obtained by Spitzig and Richmond under high pressure. Another plasticity constitutive equation with isotropic hardening model is derived from assuming a different yield function which also expresses the hydrostatic pressure dependence. The predicted results of the model are compared with the experimental ones of torsion obtained by Silano et. al under high pressure. Finally, plasticity constitutive equation is formulated by the application of kinematic hardening theory to hydrostatic pressure dependence. The predicted results of the model are compared with the experimental ones of reversed torsion under high pressure and compression after tension obtained by Kitagawa et. al.