Constitutive Equations for the Description of Creep and Creep Rupture Behavior of Metallic Materials at Temperatures Above 800 °C

At high temperatures, the creep deformation of metallic materials is correlated with the accumulation of creep damage. Creep crack growth leads to a decrease of bearing cross section and an increase in stationary creep. Both variables, creep strain rate and creep damage, are described by a system of coupled differential equations. The solutions of these equations are given for the boundary conditions of creep tests under constant load, for creep rupture behavior, for damage accumulation in the creep region, and for creep-regimed low-cycle fatigue. A general correlation between applied stress, cumulative strain, and cumulative damage is given.