Study on bending fatigue damage and life of low speed and heavy duty gears

Robert Basan proposed the mathematical model of slip line contact and the calculation model of multiaxial fatigue life 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 many described gears. The validity of the proposed model is verified. These critical values can be used to estimate the crack shape at the initial stage of crack growth and the damage type expected to develop.

He thinks that the fatigue behavior of gear represents the continuous failure process during high cycle. In his research work, a damage coupled numerical model considering the effect of IRS was developed to study the fatigue performance of gears. Based on continuous damage mechanism (CDM), the user material subroutine (UMAT) in ABAQUS is used to calculate and record the deterioration of gear material, the detailed evolution of damage and stress response during cyclic loading. The tooth contact fatigue and root bending fatigue of the gear are evaluated, and the influence of IRS on stress response and damage evolution is analyzed. The results show that the risk of surface contact fatigue failure is far greater than that of tooth bending fatigue. The initial compressive residual stress has a positive effect on the contact fatigue performance, while the amplitude of the initial tensile residual stress is 380 MPa, which can reduce the contact fatigue life by 20%.

The research of Seyit Mehmet Demet is mainly carried out on the gear with hypocycloid curve on the tooth root. He believes that the experimental study carried out in parallel with these studies is necessary to determine the fatigue life performance of these gears. In its research work, according to the static analysis of the literature, the involute gear root is manufactured by using the circular fillet method, because the root stress is better than the subcycloid tooth stress. The fatigue damage of symmetrical gears under cyclic loading and the effect of material hardness on the fatigue life of gears are studied. A specially designed single tooth bending fatigue test (stbft) device was 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, the residual tensile stress on the tooth root is high, and the crack and the root fatigue lead to fracture under low load and variable load. The residual tensile stress on the root of the teeth with a hardness of 38 HRC is slightly lower, so the fatigue life of these gears is longer than that of the gears with a hardness of 48 HRC.

Jorge M. Louren ç It is believed that the development of laser cladding technology for repairing damage is of high value due to the influence of laser cladding on fatigue and fracture behavior under variable amplitude load. Fatigue damage is the main consideration of complex Aerospace Military key components. The material Aermet was studied ® 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 carried out on 100 fatigue substrate samples. No microcracks and little porosity were observed in the coating. The fatigue test was carried out under variable amplitude load and the maximum stress was 1000 MPa. 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 compared with the baseline sample with notch, laser cladding can significantly improve the fatigue life. However, the fatigue life of the cladding sample is lower than that of the baseline sample without notch. Compressive residual stresses of 300-500 MPa were observed in the cladding area and heat affected zone. The fracture modes of cladding samples mainly include the topological surface of tearing and some debonding fracture areas through columnar austenite grains. However, PHT conditions are ineffective in improving fatigue life. The main fracture mode is cohesive fracture, which reduces the fatigue life.

The relationship between inclusions and bending fatigue behavior of 20cr2ni4 steel under different stress concentration was studied by Xing. He developed a new experimental method to prefabricate stress concentrations of different sizes near inclusions, and then carried out a new type of bending fatigue test to study the inclusions in 20cr2ni4 steel and the stress distribution around them. Combining microhardness tester with laser etching equipment, different stress concentrations were preformed 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 the 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 type was predicted. Then, according to the preformed 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 gear and 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.

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