A description of creep anisotropy induced by plastic pre-strain. 1st report. A form based on the representation theorem.

Abstract

To describe the directional effect of plastic pre-strain on creep an anisotropic creep constitutive equation was formulated on the basis of the representation theorem of rational continuum mechanics. Creep strain rate function was first assumed to be an isotropic tensor function and was written as a linear combination of tensor generators formed from deviatoric stress tensor and a second rank symmetric tensor in accordance with the polynomial representation theorem. From the general polynomial representation, a reduced constitutive relation was derived which only consisted of linear terms of the argument tensors. Special forms of a integrity basis and tensor generator were given to the reduced version which showed a similar form to the conventional kinematic hardening model. With the similar procedure, a simple evolution equation of the internal state variable tensor was also defined. The evolution equation was physically characterized so as to incorporate, in a natural way, a combined isotropic and kinematic hardening. The model was embodied by using the Bailey-Norton creep law. A comparison between predictions due to the proposed model and the experimental results for 316 Stainless Steel at an elevated temperature showed reasonable agreement with each other.