| At present,solving the problem of effective evaluation of fatigue life of urban rail vehicles under the condition of line operation has become an arduous challenge to promote the high-quality development of urban rail transit in China.Therefore,based on the rigid-flexible coupling dynamic model,this paper takes the dynamic performance of a certain urban rail vehicle and the fatigue of bogie frame as the research object,and makes dynamic analysis of the vehicle and fatigue evaluation of the frame in the whole life cycle.Combined with the evaluation results,the structure of the framework is improved.This paper mainly carried out the following research:(1)Firstly,the finite element method is used to discretize the frame structure.Considering that the local stress concentration of the weld will affect the fatigue life of the frame,the tunnel introduces the local details of the weld into the finite element model.Then,Lanczos method is used to calculate the low-order free modes of the frame,and the rationality of the structural design is judged by comparing and analyzing the relationship between the ups and downs modal frequency of the car body and the modal frequency of the frame.It lays a foundation for rigid-flexible coupling dynamic analysis and the introduction of modal structure stress method.(2)Based on the improved Craig-Bampton modal synthesis method,the flexible bogie frame model is established.Combined with the design parameters of an urban rail vehicle,the substructure models of primary and secondary suspension,nonlinear air spring(simulated by Krettek element,because this element can better restore the nonlinear stiffness and damping characteristics of air spring)and rigid car body are established.A rigid-flexible coupling dynamic model is established by connecting the car body with the flexible body frame through air springs,traction rods and other substructures.(3)In order to accurately simulate the operation conditions of the whole life cycle of the vehicle,the actual operation line data of the vehicle were counted.Considering that the actual operating line conditions of this urban rail vehicle are rather bad,the corresponding straight line and curve R280/R300/R360/R400/R450/R500/R600 line conditions were compiled with the U.S.Level 4 irregularity spectrum as the excitation,and the empty car and its capacity were investigated.The results show that the safety,stability and other indicators of the car meet the requirements of operation design.(4)Aiming at the fatigue problem of the key welding seam of the welded bogie,the quasi-static standard load in the design standard of railway bogies was used to evaluate the fatigue of the key welding seam of the frame,and then the modal structural stress method is introduced to evaluate the fatigue life of the welding seam of the frame again.The evaluation results of 66 key welds in the frame show that the fatigue life of the frame evaluated by modal structural stress method is lower,and the analysis shows that the evaluation results are closer to the actual situation because this method can consider the influence of vibration on the fatigue of the structure.Finally,based on this analysis,the structure of the frame is improved.In this paper,a rigid-flexible coupling dynamic model of a certain urban rail vehicle is established,and the modal structural stress method is introduced into the fatigue evaluation of the key welding seam of the vehicle’s welded frame.The influence of modal vibration of the frame structure on the fatigue life of the welding seam is considered,and the problem of effective evaluation of the welding seam fatigue of the bogie frame of urban rail vehicle under the condition of line operation is solved.This technology not only provides technical support for the anti-fatigue design of the welded frame of rail vehicles in China,but also can be used in other fields such as automobile,navigation and aviation. |
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