Study On Service Performance Degradation Law And Life Prediction Of Axle Box Bearing In High Speed Train

As the key parts of high-speed train running gear,axle box bearing is usually composed of outer ring,inner ring,roller,cage and grease.During the service process,the bearings need to bear the load from the train body,the traction braking load generated in the acceleration and deceleration process and various complex impact loads,which would accelerate bearing wear and reduce the fatigue life.In the face of harsh service conditions,once the bearing fails,it will seriously endanger the safety of train operation.Therefore,in order to ensure the normal operation of high-speed trains,it is very important to accurately predict the service life of axle box bearings.In this thesis,the degradation law of conventional mechanical properties and fatigue properties of axle box bearing rolling body in service of high-speed train is studied,and the remaining service life of axle box bearing is predicted.The main research contents include:(1)By referring to the overhaul standard of our high-speed train,samples of three types of bearings,new bearings,1.2 million km and 2.4 million km service,are selected.A series of experiments on fatigue,tensile and hardness are carried out respectively,and comparative analysis is conducted by combining with the micro-structure.The experimental results show that the tensile strength of three kinds of bearing steels with different service mileage are 2084 MPa,1952 MPa and 1762 MPa respectively.The10~7 cycle fatigue limits were 500±19 MPa,400±19 MPa and 294±23 MPa,respectively.The above experimental results show that the cumulative damage of bearing under alternating load has been reflected in the macroscopic mechanical parameters of materials.(2)From the micro point of view,the tensile and fatigue fracture were analyzed,and the typical features of the fracture were compared,and the frequency distribution method was used for statistics.The results show that with the increase of bearing service distance,the maximum equivalent diameter of tensile fracture surface increases,while the proportion of cleavage surface increases and the proportion of dimple decreases.The proportion of cleavage surface is 4.49%,9.75%and 12.91%respectively.The number and length of secondary cracks in the fatigue fracture increased obviously,and the median fatigue cracks were 8.3μm,9.0μm and 9.8μm,which further explained the degradation of mechanical properties of the axle box bearing after service.(3)The influence of loading sequence on fatigue life of components was analyzed and compared.Based on Miner’s Law,generalized linear cumulative damage theory was proposed,which stated that fatigue damage of components could be linearly superimposed under random load per unit mile.Based on this,the residual strength model of high-speed train bearing was established to evaluate its fatigue life.The service life of bearings calculated according to residual static strength and fatigue strength is 10 million km and 6 million km,respectively.(4)By measuring the actual size of the axle box bearing,a three-dimensional finite element model of the bearing was established,and the simulation was carried out by referring to the actual stress state of the axle box bearing in the service process of high-speed train.According to the actual bearing load and speed,the load and stress distribution of bearing roller under different working conditions were simulated.The results show that there is a linear relationship between the maximum contact stress of the bearing roller and the bearing load,and the rotating speed has little effect.The finite element simulation results were combined with the experimental S-N curves to predict the remaining service life of bearings according to the linear cumulative damage criterion.The service life of the axle box bearing under different working conditions is calculated,and its life range is 757-10.4 million km,which provides a reference for accurately predicting the life of the axle box bearing.