Structural analysis of a power plant component using a stress-range-dependent creep-damage constitutive model

Structural analysis and design of power plant components requires us to take into account inelastic deformation and material damage processes for wide stress and temperature ranges. The aim of this paper is to discuss a stress-range-dependent model of creep and damage for advanced heat resistant steels under stationary loading conditions. An emphasis is placed on the transition from the power law to the viscous creep as well as the ductile–brittle transition of the damage mode. The creep constitutive equation is proposed which includes both the linear and power-law response functions of stress. Two internal state variables are introduced to account for the material softening and brittle damage, respectively. The corresponding evolution equations are developed to fit the stress-range dependence of the creep rupture strength. To evaluate the response functions of stress and the material constants, recently published experimental data for a 9% Cr steel are applied. Examples are presented to illustrate basic features of the stress redistribution and the damage evolution in pressurized thick-walled structures. The analysis shows that for a certain specified range of internal pressure the character of the stress distribution is essentially influenced by the change of the creep deformation mechanisms. The corresponding stress levels in the steady creep state suggest that the brittle damage processes should be taken into account for the life-time estimations.