A Constitutive Model for Anisotropic Creep Deformation

Anisotropic creep behavior of polycrystalline metals under repeated stress changes is modeled from a phenomenological point of view. The creep model consists of basic constitutive equations (BCE) and an auxiliary hardening rule (AUX) to enhance the predictive capability of the BCE. The BCE is characterized by a kinematic hardening variable which is defined as the sum of two component variables; one represents the back stress and the other a flow resistance in the opposite direction of the stress deviator. The AUX is governed by a memory region in which only the evolution of the back stress takes place. The validity of the creep model is discussed on the basis of simulations for multiaxial nonproportional repeated creep of type 304 stainless steel at 650°C.