Robert Basan proposed a mathematical model of slip line contact and a multiaxial fatigue life calculation model based on Fatemi society critical interface crack initiation criterion. The developed model is applied to the meshing teeth of gears, and compared with the fatigue life of gears described in many literatures to confirm the effectiveness of the proposed model. These critical values can be used to estimate the crack shape and the damage type expected to develop in the initial stage of crack propagation.

GA 〇, Tiantang believed that the gear fatigue behavior represents a continuous failure process during high cycle. In his research work, a damage coupling numerical model considering the influence of IRS is developed to study the fatigue performance of gears. Using the user material subroutine (UMAT) in ABAQUS and based on the continuous damage mechanism (CDM), the deterioration of gear material, the detailed evolution of damage and stress response during cyclic loading are calculated and recorded. The tooth surface contact fatigue and tooth root bending fatigue of gears are evaluated, and the effects of IRS on stress response and damage evolution are analyzed. The results show that the risk of surface contact fatigue failure of the gear is much greater than that of tooth bending fatigue. The initial compressive residual stress has a positive effect on the contact fatigue performance, and the amplitude of the initial tensile residual stress is 380MPa, which will reduce the contact fatigue life of the gear by 20%.

Seyit mehmetdemet’s research is mainly carried out on gears with hypocycloid curve on the tooth root. He believes that the experimental study conducted with this well n is necessary to determine the fatigue life performance of these gears. In its research work, according to the static analysis of literature, the root of involute gear is manufactured by circular fillet method because the root stress is better than that of hypocycloid gear. The fatigue damage of symmetrical gear under cyclic load and the effect of material hardness on the fatigue life of gear are studied. A specially designed single tooth bending fatigue test (stbft) device is used for fatigue test. The results obtained from fatigue tests at low and high cycles were compared and evaluated. The results show that in the gear with HRC hardness of 48, due to the high residual tensile stress on the tooth root, cracks and root fatigue under low load and variable load. In the teeth with HRC hardness of 38, the residual tensile stress on the root is slightly lower, so the fatigue life of these gears is longer than that of gears with HRC hardness of 48.

Jorge M. louren believes that under the influence of laser cladding on fatigue and fracture behavior under variable amplitude load, it is of high value to develop laser cladding process to repair damage. Fatigue damage is the main consideration of complex Aerospace Military key components. Studied material Aermet ® 100 is an ultra-high strength steel widely used in current and next-generation aerospace components (such as landing gear). Using Aermet ® 100 powder in Aermet ® Laser cladding was performed on 100 fatigue substrate samples. No microcracks and little porosity were observed in the cladding. The fatigue test is carried out under variable amplitude load, and the maximum stress is looompa. Residual stress, microstructure and hardness were also evaluated. Cladding samples and post heat treatment (PHT) samples were compared with baseline samples with artificial notches to simulate damage. The results show that laser cladding can significantly improve the fatigue life compared with the baseline sample with notch. However, the fatigue life of cladding samples is lower than that of baseline samples without notch. Compressive residual stresses of 300-500mpa were observed in the cladding area and heat affected zone. The fracture modes of cladding specimens mainly include torn topological surfaces and some debonding fracture areas through columnar austenite grains. However, PHT conditions are ineffective in improving fatigue life. The fracture mode is mainly cohesive fracture, which reduces the fatigue life.

Xing studied the relationship between inclusions and bending fatigue behavior of 20cr2ni4 steel under different stress concentrations. It is a new experimental method to prefabricate stress concentrations of different sizes near inclusions, and then carry out a new bending fatigue test to study the inclusions in 20cr2ni4 steel and the stress distribution around them. The microhardness tester is combined with laser etching equipment to prefabricate different stress concentrations at any position around any inclusion on the surface of gear steel. This method provides an experimental basis for quantitative analysis of the relationship between stress distribution around inclusions and fatigue life of heavy gear steel. The bending fatigue life of heavy gear steel with different inclusion, stress state and spatial distribution types is predicted. Then, according to the prefabricated notch parameters and the state of inclusions in the steel, a mathematical model for quantitative analysis is proposed, which can accurately predict the fatigue limit of heavy gear steel. The research results can be applied to the actual use of heavy gears and the accurate life estimation based on gear stress state, so as to provide a quantitative reference model for subsequent gear steel production and gear parts processing.

Shi uses the software perdynamic (PD) for analyzing crack propagation in engineering material fracture to form the constitutive relationship of circumferential dynamics. The broken bond represents material fracture, but it can not be used for fatigue analysis. Based on miner’s linear cumulative damage theory, a junction medium fatigue failure criterion is proposed, which replaces the old failure criterion, and a PD fatigue failure model of high cycle fatigue is established. Finally, the bending fatigue fracture analysis of standard involute gear is carried out. The results show that the fatigue fracture process of gear by PD fatigue fracture model is consistent with the experiment. PD fatigue fracture model provides a method for fatigue crack propagation prediction and fatigue life prediction.