1) 42CrMo steel was studied by means of experiment and simulation, and various factors affecting fatigue crack propagation under different stress ratios were analyzed. A compact tensile specimen is designed for 42CrMo steel, and the fatigue crack growth test is carried out. According to Paris formula, the relationship between the stress intensity factor at the crack tip and the fatigue crack growth rate in the stable growth stage under different stress ratios is obtained, and the fatigue crack growth behavior in this stage under different stress ratios is described. The microstructure of fatigue fracture at different growth stages was observed and analyzed, and the fracture morphology characteristics at different growth stages and the influencing factors of grain on crack propagation were revealed. The finite element simulation of fatigue crack propagation is carried out, and the corresponding relationship between the stress intensity factor at the crack tip and the area and shape of the plastic zone at the crack tip under different crack lengths is described, which can accurately describe the process of fatigue crack propagation test.

2) Based on the principle of mathematical statistics, the bending fatigue life P-S-N curves of five groups of test gears are accurately obtained. The bending fatigue life of gear teeth under different reliability conditions and the functional relationship between load and bending fatigue life are obtained. It can accurately predict the bending fatigue life under different reliability and different loads.

3) Using ABAQUS software, the bending fatigue of transmission gear of heavy equipment is numerically simulated, and the collaborative comparative study of test and simulation is realized. Through finite element simulation, the stress distribution law of the tensile side and the compression side of the tooth root is revealed, the stress relationship between the tensile side and the compression side is quantitatively analyzed, the reasons for the difference of stress are clarified from the perspectives of material mechanics, geometry and mechanics, and the distribution law of stress intensity factor at the crack tip of gear is revealed from the perspectives of crack size, crack shape and load. The Miner linear cumulative damage criterion is used for simulation, and the distribution of bending fatigue life of tooth root is obtained. Through the comparison with the test, the reliability of numerical analysis is verified.