A multi-scale crystal plasticity model for cyclic plasticity and low-cycle fatigue in a precipitate-strengthened steel at elevated temperature. (2017) - Li, Dong-Feng
Abstract: In this paper, a multi-scale crystal plasticity model is presented for cyclic plasticity and low-cycle fatigue in a tempered martensite ferritic steel at elevated temperature. The model explicitly represents the geometry of grains, sub-grains and precipitates in the material, with strain gradient effects and kinematic hardening included in the crystal plasticity formulation. With the multiscale model, the cyclic behaviour at the sub-grain level is predicted with the effect of lath and precipitate sizes examined. A crystallographic, accumulated slip (strain) parameter, modulated by triaxiality, is implemented at the micro-scale, to predict crack initiation in precipitate-strengthened laths. The predicted numbers of cycles to crack initiation agree well with experimental data. A strong dependence on the precipitate size is demonstrated, indicating a detrimental effect of coarsening of precipitates on fatigue at elevated temperature. Abstract : Highlights: Multi-scale strain-gradient micromechanical modelling of cyclic plasticity and fatigue for P91 steel. EBSD measured microstructures represented in meso-scale finite element model. Lath-precipitate unit cell represented in micro-scale model. Calibration and validation against measured cyclic stress-strain evolution and fatigue crack initiation. Predicted detrimental effect of M23 C6 precipitate coarsening on cyclic strength and fatigue resistance.