In traditional elastoplastic constitutive equation with a single smooth pla
stic potential surface, the plastic stretching is independent of the tangen
tial 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 compon
ent tangential to the subloading surface is formulated by extending the sub
loading surface model with a smooth elastic-plastic transition. This model
is applicable to the analysis of deformation in a general loading process o
f materials with an arbitrary yield surface. Based on this equation, a cons
titutive equation of metals with isotropic-kinematic hardening is formulate
d and its basic characteristics are examined in detail. (C) 2001 Elsevier S
cience Ltd. All rights reserved.