Research On Fatigue Damage Of Bogie Frame Weld Of Urban Rail Rolling Stock Based On Spectrum Load

With the increasing proportion of urban rail transit in urban traffic in China,the design requirements of urban rail vehicles are becoming more and more stringent,especially for the frame structure of urban rail vehicle bogie,which not only bears the directional load from the car body,but also transmits the traction and braking load of rail vehicle.Therefore,the study of fatigue strength of bogie welded frame of urban rail vehicle is the key and difficult point of bogie design,and the result of fatigue strength evaluation is an important index of structural fatigue performance evaluation.Currently,in engineering practice,there are two types of engineering methods for evaluating fatigue strength of load-bearing structures,that is,fatigue strength evaluation based on infinite life design and fatigue strength cumulative damage calculation based on finite life design.The former uses Smith and Haigh forms of Goodman fatigue limit diagram or MKJ diagram.The latter adopts Miner linear fatigue cumulative damage theory based on S-N curve.Both fatigue strength assessment methods are used by the relevant structural fatigue strength assessment criteria,such as rail transit industry commonly used DVS1612 standard,IIW norm,BS7608 standard and EN1993-1-9 standard.To solve the local stress tensor of bogie in fatigue strength calculation,the local coordinate system of the weld structure of bogie frame is established by writing APDL language program,and the flow chart of each sub-program is given;Based on the theory of elastic mechanics,the local stress tensor of bogie frame weld structure is solved by writing FORTRAN language program.Taking the bogie frame of a city rail vehicle as the research object,combining the strength analysis load condition of the EN13749 standard and the VDV152 standard,the stress analysis of the bogie frame is carried out.According to the fatigue strength evaluation method proposed in the ERRI B12/RP17 report and the UIC510-5 standard,the projection method is used to evaluate the fatigue strength of the bogie frame.To meet the design requirements,the calculated load of the relevant standards is transformed into the spectral load of fatigue strength evaluation.Based on the fatigue evaluation methods of the BS7608 standard and the EN1993-1-9 standard,the linear cumulative damage calculation of the weld structure of the bogie frame is carried out.The two evaluation results are compared and analyzed.Finally,the fatigue strength evaluation results of "projection method" and two linear cumulative damage methods are compared,and the work flow of weld fatigue strength evaluation for urban rail bogie frame is given.The results show that the "projection method" is the same as the linear cumulative damage evaluation,and the "projection method" is the most conservative,the evaluation value based on BS7608 standard is conservative,and the evaluation value based on EN1993-1-9 standard is related to the fatigue strength coefficient.