Elastoplastic constitutive equation with tangential stress rate effect

In traditional elastoplastic constitutive equation with a single smooth plastic potential surface, the plastic stretching is independent of the tangential stress rate, i.e. the component of stress rate which is tangential to the yield surface. This traditional model predicts an unrealistically stiff response when a loading path deviates significantly from the proportional loading. In order to overcome this defect various constitutive models have been proposed. However, a pertinent model applicable to the description of the deformation behavior in a general loading process has not been proposed up to the present. In this article, an elastoplastic constitutive equation with the inelastic stretching induced by the deviatoric stress rate component tangential to the subloading surface is formulated by extending the subloading surface model with a smooth elastic–plastic transition. This model is applicable to the analysis of deformation in a general loading process of materials with an arbitrary yield surface. Based on this equation, a constitutive equation of metals with isotropic-kinematic hardening is formulated and its basic characteristics are examined in detail.