Modeling of secondary creep behavior for anisotropic materials with different properties in tension and compression

A constitutive model is developed to describe the anisotropic secondary cre ep response of polycrystalline metals and alloys with different behavior in tension and compression. The equivalent stress in the general anisotropic potential contains the linear and quadratic joint invariants of the stress tensor, and the second order and fourth order material tensors. In describi ng the creep behavior of orthotropic materials for the special case of coin cidence of the coordinate axes with the principal directions of anisotropy, a nine parameter expression for the equivalent stress is proposed with the corresponding constitutive equation of creep. The determination of the mat erial parameters in the proposed creep equation is obtained from a series o f basic experiments outlined in this work. The results generated from the m odel are compared with those from experiments under multiaxial loading for various metallic materials. (C) 1998 Elsevier Science Ltd. All rights reser ved.