The fatigue crack growth mechanism of 42CrMo steel was studied by fatigue crack growth test. The law of fatigue crack growth rate under different stress levels was compared and analyzed. Paris formula of fatigue crack growth in stable growth stage was calculated and verified by numerical simulation; The fatigue life of low speed and heavy load gear was deduced by bending fatigue test. The fatigue fracture was observed and analyzed by scanning electron microscope, and the effect of microstructure on crack propagation and fatigue life was obtained. The main research contents are as follows
1) The fatigue crack growth test of 42CrMo steel compact tensile specimen under different stress levels and the data characteristics at different growth stages were studied. The Paris formula of stable growth stage was obtained.
2) Through the numerical simulation method, the fatigue crack growth process of compact tensile specimen is simulated, and the relevant data in the fatigue crack growth process are obtained, and compared with the test results to verify the accuracy of the test, which lays the foundation for the following low-speed and heavy-duty gear bending fatigue test and gear fatigue life inference.
3) The bending fatigue test of the low-speed and heavy-duty gear designed and manufactured under different stress levels is carried out, and the relevant test data are recorded. The fatigue life and fatigue limit of the test gear under different reliability are obtained by analyzing the S-N curve with relevant mathematical statistics knowledge.
4) The macro and micro morphology of fatigue fracture of low speed and heavy load gear after fatigue failure were observed and analyzed, and the effects of microstructure characteristics and material defects on crack initiation and fatigue life at different growth stages were obtained.