Damage-Coupled Cyclic Plasticity Model for Prediction of Ratcheting–Fatigue Behavior under Strain and Stress Controlled Ratcheting for Two Different Nuclear Piping Steels.

In this present work, a damage-coupled cyclic plasticity model has been developed for more accurate ratcheting–fatigue life estimation under strain and stress controlled ratcheting. Ratcheting–fatigue damage behavior under uniaxial multistep strain-controlled ratcheting shows that the incremental mean ratcheting strain deteriorates the elastic slopes cycle by cycle, by means of ratcheting damage. Severe ratcheting strain accumulation rate has been observed in tertiary region under uniaxial stress controlled ratcheting. The proposed damage-coupled model has been constructed which incorporates both fatigue damage and damaging effect of the accumulated mean plastic strain. The proposed model incorporates a critical fatigue damage parameter which can predict effects of early fatigue crack nucleation due to combined ratcheting and fatigue damages. The performance of the proposed damage-coupled model has been investigated in the present study based on the critical fatigue damage parameter. The proposed model is calibrated on experimental data of SA333 Gr. 6 carbon steel and SA508 Gr. 3 steel. The proposed formulations have been applied in user material subroutine UMAT of finite element software, ABAQUS. The proposed model has been validated by comparing predicted ratcheting behavior with experiments for the two different steels. All the predicted number of cycles to failure are located within 0.5 times error band. The proposed damage-coupled model has demonstrated excellent capabilities of predicting ratcheting–fatigue life under cyclic loading with ratcheting damage. [ABSTRACT FROM AUTHOR]