Stress regime-dependent creep constitutive model considerations in finite element continuum damage mechanics

Structural analysis and the design of high-temperature components require the consideration of material inelastic deformation and damage accumulation characteristics for a wide range of stresses and temperatures. For many engineering alloys, the creep deformation/damage accumulation mechanism exhibited at high stresses are not the same as those at lower stresses. This article explains the importance of considering this stress regime dependency in the creep model formulations and introduces a new (primary-secondary-tertiary) creep model which considers a gradual change of creep deformation/damage accumulation mechanism with stress variation. Application of the new stress regime-dependent creep model formulation in finite element continuum damage mechanics to simulate creep deformation/damage accumulation in a series of creep crack incubation tests involving fracture mechanics compact tension specimens shows a good agreement with experimental observations which was not achievable by considering conventional single-regime creep model equations.