Research On Wheel Fatigue Reliability Assessment Of The High Speed EMU Under Low Temperature

Wheel tread peeling and rim cracking are the main rolling contact fatigue failure modes of high speed EMU(Electrical Multiple Unit)wheels,which seriously threaten driving safety of EMU.While low-temperature environments have a significant impact on the fatigue limit and crack growth rate of wheel.Therefore,it is of great significance to evaluate the fatigue reliability of EMU wheels under low-temperature service conditions.CRH5 EMU wheels were taken as the research object,and fatigue life prediction and fatigue reliability evaluation under low-temperature service conditions were carried out.A wheel-rail rolling contact model had been established.Further,a method for evaluating high speed EMU wheel fatigue reliability had been proposed;through a combination of experiment and simulation,the low-temperature fatigue life of the wheel was calculated and the influence law of the random wheelset lateral displacement,wheel rail frictional heat and random vertical load was studied.The low-temperature fatigue reliability evaluation results of the wheel were obtained to provide a reference for maintenance strategy formulation of EMU wheels under low-temperature service conditions.Considering the influence of the-40℃ low temperature environment on the fatigue performance of the wheels,the P-C-S-N curves of whole life interval of the EMU wheels were determined by the group method and the up-down method of low-temperature fatigue test of the R8 T steel fatigue specimens,combined with mathematical calculation and extrapolation.Then the wheel strength distribution parameters could be derived.The obtained parameters are used as the basis for wheel fatigue life prediction and fatigue reliability evaluation.Based on the research of the existing finite element wheel-rail contact simulation model,an implicit and explicit co-simulation model of wheel-rail rolling contact had been established to solve the wheel-rail rolling contact problem of EMU under low-temperature service conditions and determine the stress and strain state of the critical part of the wheel.Compared with the calculation speed of the existing contact model,the established co-simulation model can be used to solve the wheel-rail contact problem of elastic-plastic material/elastic-plastic thermal coupling material with different creep rates from rolling to sliding,while the speed of the co-simulation model is increased by 2 times.In order to determine the influence of three common factors including random wheelset lateral displacement,wheel-rail friction heat and random vertical load on the fatigue life of wheels during the operation of the EMU,the co-simulation model was used to perform wheel-rail rolling contact calculation under different working conditions;Combined with Liu’s multiaxial fatigue model and wheel P-C-S-N curves,EMU wheel fatigue life was predicted.Quantitatively study the influence of 3 factors on wheel fatigue life shows that the critical part of wheel is 1.5mm under the thread,the random lateral displacement of the wheelset decreases the predicted value of wheel fatigue life by 57%,and the increase of vertical load reduces the predicted value of wheel fatigue life significantly,while the wheel-rail frictional heat has few effect during the normal operation of the EMU.Based on the analysis of the factors affecting the low temperature fatigue life of EMU wheels,a wheel fatigue reliability evaluation method had been proposed considering the influence of the random lateral displacement of the wheelset and the random vertical load at the same time.The functional relationship among the multiaxial equivalent stress,lateral displacement and vertical load at the critical part was determined by fitting the calculation results of the co-simulation model.Combined with EMU wheel strength distribution,Monte Carlo simulation was used to calculate wheel fatigue reliability.Result shows the reliability is 83.87% at 2.8E5 km mileage with 99% confidence.It means that under the existing maintenance strategy,the wheels of CRH5 EMU have the risk of contact fatigue failure when they are used in low temperature service conditions,failure probability is about 17%.The above research results provide a new method for evaluating the fatigue reliability of EMU wheels,and can provide a reference for the inspection and maintenance strategy formulation of EMU wheels,ensuring EMU operation safety,and can also be promoted to solve bearing rolling contact fatigue reliability evaluation problems.