Hysteretic energy damage coupled elastoplastic constitutive model and its application to low-cycle fatigue life prediction of martensitic steel

The microstructure of martensitic steel is analyzed by transmission electron microscopy and X-ray diffraction. The low-cycle fatigue (LCF) test of martensitic steel with different strain amplitudes is carried out by MTS universal hydraulic servo testing machine. The damage accumulation and cyclic elastic-plastic constitutive model of martensitic steel are studied. The influence of tempering on hysteretic loop and fatigue damage is discussed. With the tempering temperature increasing, the area of hysteresis loop increase, the hysteresis energy increases, and the fatigue life decreases. According to the fatigue damage accumulation model of the hysteresis energy method, an improved kinematic and isotropic composite hardening model is proposed in tempering temperature. This model is used to simulate the LCF behavior before fracture under LCF load and to predict the fatigue life with the variation of applied strain amplitude and tempering temperature. The verification results show that the modified model can well describe the phenomenon of acceleration of cyclic softening and great reduction of cyclic stress.