Research On Fatigue Life Prediction Of Axle Box Cover Bolts Of Metro Vehicles

With the development of economy and the expansion of cities,the subway has become an increasingly important means of transportation.In the operation of metro vehicles,the axle box cover is subjected to the alternating load,which causes the fracture of the axle box cover bolt,which affects the safety of the vehicle operation.In order to determine the cause of the fracture of axle box cover bolt and evaluate the effect of the potential governance measures,it is necessary to carry out systematic research.After field investigation,the basic situation of the fracture of axle box cover bolt was mastered.The bolt fracture morphology is analyzed and the working strength of bolts is checked,and it is found that the fracture of axle box cover bolt belongs to high cycle low stress fatigue fracture.It is one of the main reasons for the failure of the axle box cover bolt that the vibration of the axle box caused by the wheel rail is not smooth,and the vibration is passed through the bolt to the cover of the axle box.Through the analysis of the wheel out of roundness,rail irregularity,vehicle speed and axle box vibration acceleration,the relationship between rail irregularities found the influence of vibration of axle box dominate,also found that change the vehicle running speed can significantly reduce axle box vibration level.The fatigue life prediction model of axle box cover bolts with axial box vibration acceleration is established.The model takes the vibration acceleration of the measured axle box as the input condition,and the bolt hazard point stress calculated by the three dimensional solid finite element calculation of the axle box,axle box cover and axle box cover bolt is the evaluation object.With fracture bolt should be determined on the basis of the statistical life bolt structure fatigue damage coefficient.Bolt fatigue life prediction model with finite element method to calculate the transient bolt stress of the dangerous point time course load(history),with the rain flow count method statistics statistical bolt stress load spectrum,the linear cumulative damage theory was used to assess the load and the relationship between the damage accumulation,finally,produce the damage equivalent mileage conversion bolt fatigue life.Determining the structure fatigue damage coefficient,fracture bolt will predict life and life expectancy fixed bolt structure fatigue damage coefficient,the difference between the repeated iteration,until the predicted life and fracture bolt the difference between the average life expectancy in the allowable error range.Using axle box cover bolt fatigue life prediction model is established,and studied the rail irregularity amplitude,vehicle speed,material and bolt connection status of bolt fatigue life are studied.This paper analyzes the contribution of improving the fatigue life of the bolt by controlling the rail wave mill,changing the speed of the vehicle,or improving the bolt material.