Damage Coupled Constitutive and Finite Element Modeling of Uniaxial LCF and Ratcheting for Nuclear Piping Steels

Abstract

The objective of this present study is to develop a damage-coupled constitutive and finite element model for the prediction of cyclic plastic behaviors and fatigue life under different uniaxial loading conditions. Uniaxial symmetric and asymmetric strain/stress-controlled loading cycles have been analyzed carefully to understand different cyclic plastic characteristics in the LCF regime which include strain range dependent cyclic hardening/softening, relaxation of mean stress, ratcheting under stress/strain controlled conditions and post ratchet strain cycling, and additional hardening.. Quantitative investigations of yield surface evolution have been carried out for SA333 Gr. 6 carbon steel. The material exhibits cyclic yield variation, depending on range of strain and higher translations of the centre of yield surface (back stress variation) for higher strain ranges. A multi-objective cyclic plastic model has been developed that can predict the hardening and softening behaviour of the material throughout the deformation, i.e., in primary, secondary, and tertiary regions, with reasonable accuracy. The proposed model has incorporated the additional hardening characteristics and demonstrated a good correlation with experiments. Also, the proposed model has showed significant improvement compared to the Ohno-Wang model. newlineThe proposed formulations have been implemented in UMAT of ABAQUS. The proposed damage-coupled model has demonstrated excellent predictions of ratcheting-fatigue behavior and fatigue life under cyclic loading with ratcheting damage for the two different nuclear piping steels. newline newline