| In the service process of domestic intercity EMUs with a designed speed of 200 km/h,class I and class II rolling contact fatigue damage of wheels occurred accompanied by problems such as asymmetric wear of wheel flange and so on.In view of the above problems,an intercity EMU was selected,and a wheel profile comparison monitering in one re–profiling period was carried out on an operation line.LM and LMA wheel profiles were used to study their influence on wheel rolling contact fatigue damage behavior.Taking the above field test as background,this thesis showed the wheel tracking test results during the test in detail,summarized the differences and trends of the rolling contact fatigue damage of the two profiles of wheels.Using the survey results,a dynamics model of EMU with the ability of wheel rolling contact fatigue prediction was established and revealed the root causes of the differences of the rolling contact fatigue damage of the two profiles of wheels from the mechanism level.Finally,the influencing factors of wheel rolling contact fatigue are studied.The specific research contents are as follows:Firstly,the research literatures related to wheel rolling contact fatigue were summarized,including the mechanism and classification,research methods and prevention measures of wheel rolling contact fatigue,and the research ideas of this thesis were determined by referring to the commonly used research methods in relevant fields.In the wheel profile comparison test,an intercity EMU with a designed speed of 200 km/h was selected,the first vehicle to the fourth vehicle used LMA wheel profile and the fifth vehicle to the eighth vehicle used LM wheel profile,and equipped with corresponding anti hunting shock absorbers.A total of 10 tracking tests were carried out for 11 months,and the wear profile and tread state of the two profile wheels were recorded.Through statistics and correlation analysis,the profile evolution law and rolling contact fatigue damage law of the two profile wheels were summarized,and the correlation conclusions among rolling contact fatigue and running mileage,motor as well as trailer,wheel position and profile evolution were obtained.The results showed that in the tracking re–profiling period,the rolling contact fatigue of LMA profile wheel basically did not appear,while the rolling contact fatigue of class I and class II occured in LM profile wheel.The fatigue area of class Ⅰ and Ⅱ was located at 5–17mm outside the nominal rolling circle and 16–28 mm inside the nominal rolling circle respectively.With the increase of running mileage,class I and II fatigue areas gradually moved away from the nominal rolling circle.However,the condition of rolling contact fatigue remained basically stable.Class I and II rolling contact fatigue on LM profile wheels were concentrated on even and odd side wheels respectively,and mainly occured on the wheels of the first as well as last vehicles and motor vehicles.Based on the tracking test data,the vehicle dynamics simulation model for the above intercity EMUs is established,and the prediction results of the dynamics model are introduced into the damage function model to realize the initiation prediction of class I and class II rolling contact fatigue of wheels under different working conditions.Using this numerical simulation method,the influence of LM and LMA wheel profile on class I rolling contact fatigue is analyzed in detail.Based on the conclusion of statistics and correlation analysis,the research focuses on the influence of curve radius,wheel rail profile evolution,motor as well as trailer and other factors.The research showed that:(1)The sharp curves with a radius less than 550 m on the service delivery road of intercity EMUs were all right curves.When the EMUs ran at a constant speed through the sharp curves,the wheel–rail interaction on the low rail side of the guiding wheelsets caused the wheel appearing clsss I rolling contact fatigue.Before 80,000 km after wheel reprofiling,there was no significant difference in the rolling contact fatigue damage peak of the two profiles,but after that,the class I rolling contact fatigue damage peak of LM profile was higher than that of LMA profile.The difference of class I rolling contact fatigue damage between the two profiles was mainly due to the different wear and deformation process of the profile.For example,after 80,000 km after wheel reprofiling,the contact spot of LM profile wheel was narrower than LMA profile,resulting in higher damage peak value.With the increase of running mileage,the peak value of rolling contact fatigue damage of the two profiles basically fluctuated in a certain range.(2)When the new wheel was matched with the new rail,the class I rolling contact fatigue zone of LM and LMA profile wheels was located at 0–24 mm and 14–25 mm outside the nominal rolling circle respectively;Compared with the working condition of new wheel and new rail,with the increase of running mileage,the wear deformation made the fatigue zone gradually move outward,as far as 33 mm.Compared with trailer wheels,motor vehicle wheels with two profiles were more prone to producing class I rolling contact fatigue.(3)Properly increasing the axle load,reducing the longitudinal stiffness of the primary suspension and reducing the friction coefficient could reduce the severity of class I rolling contact fatigue of wheels in a certain range.It should be pointed out that the above simulation results were in good agreement with the field observation results,but the damage function used in the prediction model underestimated the wear in reality.Therefore,the simulation predicted that the LMA profile would appear class I rolling contact fatigue,but it was not observed in practice.In addition,the fatigue area observed in the field was usually narrower and less fatigue than that predicted by the simulation.In addition to the above class Ⅰ rolling contact fatigue,the influence of LM and LMA profiles on class II rolling contact fatigue was also simulated and studied in this thesis.The research indicated that:(1)When the vehicles passed through the sharp curves,the wheel–rail interaction on the high rail side of the guiding wheelsets was the root cause of class II fatigue at the root of the wheel flange.(2)Before 40,000 km after wheel reprofiling,there was no obvious difference in rolling contact fatigue resistance between the two profiles,but after that,the damage peak of LM profile was always higher than LMA profile,and the fundamental reason was also the difference of wear and deformation between the two profiles in service.With the increase of running mileage,the peak value of class II rolling contact fatigue damage of the two profiles basically fluctuated in a certain range without obvious jump.(3)When the new wheel was matched with the new rail,the class II rolling contact fatigue zone of LM and LMA profile wheels was located within the range of 10–25 mm and 10–30 mm inside the nominal rolling circle respectively.With the increase of running mileage,the fatigue zone gradually moved to the root of the wheel flange on the basis of the above range.The possibility of class II rolling contact fatigue of motor vehicle wheels was also higher than that of trailer wheels.(4)Properly increasing the axle load,reducing the longitudinal stiffness of the primary suspension and reducing the friction coefficient could alleviate class II rolling contact fatigue in a certain range.It should be pointed out that the above simulation results were also consistent with the field observation results.Considering the on–site wheel wear effect,it could be explained that there was no class II rolling contact fatigue crack in the LMA profile in the test.Finally,the main task of this thesis was summarized and the future research direction was proposed. |
PDF Full Text Request