Novel direct method on the life prediction of component under high temperature-creep fatigue conditions

This paper presents a novel direct method, within the Linear Matching Method (LMM) framework, for the direct evaluation of steady state cyclic behaviour of structures subjected to high temperature – creep fatigue conditions. The LMM was originally developed for the evaluation of shakedown and ratchet limits. The latest extension of the LMM makes it capable of predicting the steady state stress strain solutions of component subjected to cyclic thermal and mechanical loads with creep effects. The proposed iterative method directly calculates the creep stress and cyclically enhanced creep strain during the dwell period for the assessment of the creep damage, and also creep enhanced total strain range for the assessment of fatigue damage of each load cycle. To demonstrate the efficiency and applicability of the method to assess the creep fatigue damage, two types of weldments subjected to reverse bending moment at elevated temperature of 550C are simulated by the proposed method considering a Ramberg-Osgood model for plastic strains under saturated cyclic conditions and a power-law model in “time hardening” form for creep strains during the dwell period. Further experimental validation shows that the proposed direct method provides a general purpose technique for the creep fatigue damage assessment with creep fatigue interaction.