A constitutive model taking account of non-symmetric creep behavior in tension and compression

A multiaxial constitute model that distinguishes between creep-damage behaviors of a class of polycrystalline metallic materials under tensile and compressive stress states is developed from phenomenological points of view. The formulation is achieved by modifying the coupled creep-damage model based on the von Mises stress criterion. The effective stresses of the von Mises type that control the rates of creep and damage are scaled, respectively, to show asymmetry in tension and compression. For this purpose, anisotropic scaling parameters are introduced which depend on the hydrostatic stress and the third invariant of the stress deviator. Two kinds of modified version of the coupled creep-damage model are presented which consider kinematic and isotropic hardening of materials, respectively. These new models describe the primary, secondary and tertiary creep behavior with asymmetry in tension and compression. Numerical simulations of creep behavior under constant and variable stress conditions are also carried out.