A unified viscoplastic constitutive model with damage for multi-axial creep-fatigue loading

A unified viscoplastic constitutive model with damage is presented to describe creep-fatigue deformation behavior. The primary improvement on the existing models is to introduce creep and fatigue damage variables into the constitutive equations of adapted complexity. The material model, which is developed from the thermodynamic framework, combines nonlinear isotropic and kinematic hardening variables, and is implemented using a user-defined subroutine. A standard specimen and a hollow cylinder are used to carry out uniaxial and multi-axial creep-fatigue tests to validate the material model. Good agreement is obtained between the simulation and the measurement under various thermo-mechanical loading paths.