Fatigue Reliability Improvement Of B-type Metro Frame Based On Damage Uniform Load Spectrum

With the high-speed development of industrialization and urbanization,as the most important part of urban traffic,more and more attention are paid to the safety of metro vehicles.With the increase of operating mileage,the insufficient fatigue strength of some domestic metro vehicles' bogies has gradually come out.Therefore,it is very necessary to analyze the operating status and load characteristics of metro vehicles,so as to accurately evaluate the fatigue reliability of the frame.In this paper the B-type metro bogie of a certain line is taken as the research object,and the following research work is carried out:Firstly,the finite element model of the motor bogie frame is established.Based on the strength design standard JIS E4207,the static strength and fatigue strength of the motor bogie frame are analyzed.The results show that under the action of supernormal load,the maximum stress on the frame occurs at the angle end between the upper cover plate of the gear box hanger and the cross beam;under the action of supernormal load with 5 g longitudinal acceleration of the bogie,the maximum stress on the frame occurs at the angle end between the cover plate of the traction tie rod seat and the cross beam,and these stresses are less than the yield stress in the welded zone of the bogie material,and the static strength of the frame meets the requirements.The dynamic stress amplitude of the whole frame are less than the fatigue limit of the corresponding base metal and the grinding weld,and the fatigue strength of the frame meets the requirements.Secondly,based on the line test,the dynamic stress response characteristics of the bogie frame are obtained,the main frequencies at each measuring point in the connecting area are 42Hz and 51Hz,which are basically consistent with the first and second natural frequencies of the frame.It shows that the resonance phenomenon occurs in the cross-beam area and the connection area of cross-beam and side-beam during the running of the vehicle.The fatigue life of each bogie frame in the cross-beam connection part,the vertical stop and cross-beam connection part,the motor suspension plate and cross-beam connection part,and the gear box suspension plate and cross-beam connection part is less than 3.6 million kilometers.Thirdly,The load spectrum of metro bogie is obtained through the processes of calibration test,main line test,statistical compilation and damage consistency check.The proofed load spectrum stress and the measured equivalent stress of the bogie frame almost distribute between 1.0 and 1.5,which shows that the load spectrum can not only satisfy the damage condition of the structure in service,but also very close to the true stress condition of the frame.Under EN and UIC Standard,the ratio of stress to measured equivalent stress distributes in a wide range from 0.5 to 3.Both of them can not effectively evaluate the damage condition of the bogie structure in service.Fourthly,The structure of bogie is improved and re-tested.The results showed that the fatigue reliability of some measuring points can not meet the service requirements of 3.6 million kilometers,which are at the connection position of cross-beam and side-beam,otherwise at the connection position of cross-beam and motor hanger or at the variable cross-section position of side-beam.The fatigue reliability of all measuring points at the connection position of cross-beam and small longitudinal beam or at the connection position of cross-beam and gear box hanger can meet the service requirements of 3.6 million kilometers.Almost all measuring points meet the service requirements of 2 million kilometers.