Study On Impact Fatigue Life Of High Speed EMU Under Low Temperature Service Condition

The speed of high speed EMU is becoming faster and faster and the environment of the line is increasingly harsh.While the wheel is one of the key parts of high-speed EMU,and its safety and reliability requirements are increasingly high.The performance of high speed EMU wheel is acceptable at room temperature,while high speed EMU wheel easy to form the flat at low temperature,which is safe and reliable under low temperature conditions are not verified.Therefore,the paper takes the wheel of high speed EMU as the research object under the low temperature condition,analyzing the mechanism and influence of wheel forming flats,the wheel-rail impact caused by wheel flats,and fatigue failure of wheel caused by periodic wheel-rail impact after wheel forming flats.They have important engineering significance to the operation safety of high-speed EMUs in China.Based on the study of the CRH5 type high speed EMUs in Harbin to Dalian passenger dedicated line,the cause of the wheel flat is determined by force analysis and fault tree analysis.And taking the effect of non steady state heat conduction between the wheel and rail,thermal convection between the wheel/rail and the environment and the thermal radiation of the wheel/rail into account,considering the material properties changing with the temperature,the paper uses the direct coupling method establishing a three-dimensional wheel/rail contact elastic plastic thermal-structural coupling finite element model to analyze the mechanism and influence of wheel forming flats.Furthermore,the paper researches the influence of different friction coefficient,low environment temperature and relative sliding/rotating speed on the wheel forming flats.Finally,the cause of wheel-rail impact after wheel forming flats is analyzed by using analytical method,which provides basis for subsequent analysis of wheel-rail impact caused by wheel flats at low temperature.According to the basic parameters of the Harbin passenger dedicated line CRH5 type EMU,the dynamic model of vehicle track system is established based on multi-body dynamics software SIMPACK,and the model considers the influence of wheel radial size changes on the wheel rail contact.The paper uses variable wheel diameter method to simulate the wheel flats,using the change of suspension parameters to simulate the change of low temperature.The paper analyzes the wheel-rail impact response caused by the single wheel flat and multiple wheel flats.Furthermore,the influence of the low temperature environment temperature,flat length and vehicle speed on the wheel rail impact is analyzed.In addition,the allowable limit of wheel flats of CRH5 type high speed EMU is also given.The study provides the basis for the study of the wheel rail impact characteristics of the high speed EMU and provides the conditions for the subsequent analysis of the abrasion wheel fatigue life.The paper modifies the previous vehicle track system model to obtain the random load time history of the wheel without flats.And the wheel-rail impact load time history is obtained in the front analysis.According to the material S-N curve,combined with finite element quasi-static superposition method,by using FATIGUE tool in ANSYS WORKBENCH,the fatigue life of the wheel without flats and the wheel having flats are analyzed,and the fatigue life of the abrasion wheel is evaluated.The results of this study can be used to evaluate the impact fatigue life of the CRH5 type high speed EMUs in Harbin to Dalian Passenger Dedicated Line.And it can be applied to the study of the impact fatigue life of other typological high speed EMU.