Crack Growth Analysis And Residual Life Prediction Of Helical Gear In Transmission System Of Metro Vehicle

The development of urban rail transit plays an important role in the rapid development of society.As an important part of urban rail transit,the operation quality of metro vehicles is particularly important.As an important part of metro vehicle transmission system,gear plays an important role in the normal operation of metro vehicle transmission system.Its operation directly determines whether the subway vehicles can run safely.With the continuous increase of the total operating mileage of urban rail transit in China,the probability of bending fatigue fracture of gear teeth i n the transmission system of metro vehicles is increased,which seriously affects the operation safety of metro vehicles.Once the subway vehicle in the operation process,the transmission system gear bending fatigue damage,will bring huge economic losses to the country and society.Therefore,it is of great significance for the development of urban rail transit to carry out the research on the bending fatigue mechanism of helical gears in the gearbox of metro vehicles and to propose a new method for predi cting the bending fatigue life of gears.The research content of this paper is as follows:1.The finite element model of helical gear engagement of metro vehicle gearbox is established by using ANSYS software,and the transient dynamic analysis of helical gear engagement process is carried out.According to the output torque of AC motor in the start-up stage of metro vehicle,the stress distribution and change of helical gear in different speed range are analyzed,and the crack initiation position of helic al gear root of metro vehicle is obtained The speed range at which the train has the greatest influence on the root crack initiation at the start-up stage.Then,by establishing a local coordinate system at the node where the maximum main stress occurs,the distribution of the root stress along the normal direction and the end direction of the helical gear is further analyzed,and the failure mode of the root crack initiation is obtained.2.Taking the helical gear box of metro vehicle as the research objec t,the propagation and change rule of the crack at the end surface of the root of the helical gear is studied.The finite element model of three-dimensional crack growth with initial crack at the tooth root end surface is established by using ANSYS softwar e,and then the three-dimensional crack growth path at the tooth root end surface of helical gear is simulated by using XFEM theory,and the propagation law of the crack at the tooth root of helical gear is deeply explored.Finally,the load,the angle of initial crack and the change of crack growth path are deeply analyzed Change the relationship between laws.3.Based on the finite element model with initial crack at the end face of the tooth root,the stress intensity factor of the leading edge of the semi elliptical crack is calculated by the finite element method.The key parameter stress intensity factor in the process of crack growth is analyzed in detail,and the change rule of the stress intensity factor of the crack initiated at the end face of the tooth root is obtained.On this basis,the influence of the load,the radius of the short axis of the crack and the angle of the initial crack on the change of the stress intensity factor is studied.4.On the basis of the prediction model of gear residual strength put forward by predecessors,considering the influence of the size influence relationship between high and low cycle loads on the gear residual strength,the influence coefficient between loads is introduced into the model to improve the model,and the improved prediction model of gear residual strength is obtained after detailed formula derivation.Finally,the two-stage loading of gear is adopted In the experiment,20%,40%,60% and 80% are selected as the damage of the gear under the first level load to verify the accuracy of the improved model in predicting the residual strength of the gear under the second level load,so as to verify the accuracy of the improved model.The test results show that under the condition of two-stage loading,no matter the loading sequence is high-low or low-high,the improved model proposed in this paper is more accurate than the former model in the fitting between the predicted value and the test value of gear residual strength.Based on the operation condition of metro vehicles,this paper analyzes the stress distribution and change mode of the helical gear pair in the operation process of metro vehicles,explores the law of the crack propagation path of the helical gear root,analyzes the stress intensity factor of the crack initiation at the helical gear root,and puts forward a kind of gear bending The prediction model of residual strength of bending fatigue is established,and the effect of the model is verified by experiments.