The Ratchetting Study Of15CrMoR

The uniaxial tensile test and the uniaxial ratcheting experiment for15CrMoR were studied at20℃,200℃,300℃and400℃. According to the results, the effect of environmental temperature and loading rate on mechanical properties of materials is complex. When the loading rate remains constant, the higher the temperature goes, the shorter the yield platform is. The material yield length and temperature platform exhibits an exponential relationship. According to the result of the experiments of cyclic plasticity within the fatigue life at different temperature, the ratcheting strain rate keeps stable for a long period of the asymmetrical cyclic loading, but increases rapidly near the final failure period. In asymmetrical stress cycling, ratcheting strain rate of the material is increase with the ascendant of the mean stress and stress amplitude. Low cycle fatigue life was influenced by both the mean stress and the stress amplitude, but more by the latter. The prediction of the fatigue life by the MSRS model is more accurate compared with the Coffin-Manson model and the modified Morrow model. The MSRS model with the temperature parameter, which is based on MSRS model and taking the influence of temperature on model parameter, will be more convenient in calculating the fatigue life at different temperature.According to the study of the morphology of fatigue fracture of15CrMoR at different temperature and under different load, we discover that when the material ratcheting strain rate is bigger than0.001%/s, ductile fracture frequently happens, when the material ratcheting strain rate is smaller than0.001%/s, fatigue fracture is the dominant reaction. The study of the crack propagation region reveals that there are many secondary cracks of transgranular fracture. Furthermore, when the stress is bigger, the secondary crack is fewer, although the secondary crack is much longer, deeper.According to the tensile experiment and ratcheting experiment data, we identified parameters of the OW-Ⅱ model. By introducing damage variable, we determined the OW-Ⅱ model with damage. This model will be more effective in predicting the ratcheting effect of15CrMoR at different temperature.