Research on Creep Constitutive Model and Creep-Life Calculation Method for Steels

Abstract

Creep deformation and creep rupture is essential for the safety of steels working at high temperatures. Considering the practical creep rate curves and classical theta projection method, a generalized creep constitutive model with two critical creep time points and six stress-dependent parameters has then been proposed to describe typical creep curve styles. P92 and T92 steels are taken as the examples to verify that this model can represent and predict creep behaviors in a unified and smooth way. By means of interpolation functions for eight creep parameters, it is found that fitting functions should be separated by a critical creep stress, which is smaller than yield strength of material. Based on creep damage model, two creep-life calculation methods have been established corresponding to considering the creep deformation or not. Comparisons between two creep-life methods illustrate that creep deformation speeds up creep damage accumulation by increasing the true stress. Moreover, critical creep stress is also the turning point in the bilinear graph of creep-life curve, which means that damage accumulation styles are different for stress larger and smaller than critical stress.