Structural Fatigue Reliability Research On Motor Bogie Frame Of China Standard EMUs

As the key bearing component of high speed EMUs,bogies are subjected to complex alternating loads in practical application.Long-term effects of alternating loads will cause damage to the bogie and accumulated gradually.When the damage reaches a critical value,the fatigue failure will occur,which seriously endangers driving safety.Standard EMU,as a newly designed iconic product with completely independent intellectual property rights,it’s profoundly significant to set up a database of stress changes over time in service of its key components for optimizing the design,setting a reasonable maintenance cycle and formulating structural strength design specifications and reliability test evaluation standard.Therefore,it’s very important to evaluate the fatigue life and strength of the vehicle bogie frame.In this paper,motor bogie frame of CR400BF standard EMU was taken as the research object,and the long term on-track dynamic stress test of the high-speed train was carried out on Daxi,Zhengxu,Hada,Jingguang passenger dedicated lines to obtain the measuring data.Combining FEA and other research methods with on-track test,the research for the fatigue reliability of the frame was carried out.The main contents are as follows:(1)The structrual characteristics and basic parameters of the motor bogie frame were introduced,the dynamic stress analysis methods and stress spectrum compilation method and some calculation results were elaborated as well.According to the relevent research experience,the distribution of measuring points was determined,and the on-track dynamic stress test equipments and test contents were explained.(2)Combined with the results of modal and wheel-rail disturbance,the dynamic stress characteristics and the relationship between stress and load in typical conditions were analyzed by time domain and frequence domain.The factors significantly affect the fatigue life were discussed from the time-frequence point of view.(3)Based on the equivalent stresses,the reliability evaluation measuring points of the frame were selected,and the regularity of the equivalent stresses of the evaluation measuring points under typical conditions were determined,and the measuring data of Hada line was selected to evaluate the fatigue reliability of the frame.The measured stress spectrums of typical measuring points on Hada line were prepared,then fitted and tested by Weibull distribution.The maximum stresses and expanded stress spectrums at total number of 106 cycles were deduced.Based on the finite element calculation results,the amplitudes of the expanded spectrums were converted to equivalent symmetrical cycle stress amplitudes and the modified spectrums were obtained.On the basis of this,the extended stress spectrums of 15-million-kilometer operating mileage were obtained by utilizing the proportional relationship between the number of cycles and the operationg mileage.And the damage values of typical measuring points were calculated to predict the fatigue life of the frame by using the Miner linear cumulative damage theory and IIW standard.The research results provide references for the development of the serialized products of standard EMUs,which has important significance in engineering applications.