Research On The Vibraton Fagtigue Of A High-speed Train Carbody Based On The Rigid-flexible Coupled Theory

In recent years,China’s high-speed railway has developed rapidly and completed an important stage from introduction,digestion and absorption to independent innovation.The body of high-speed train is an important bearing part of the train,and its structural reliability is directly related to the overall reliability of the vehicle system.With the increase of train running speed and the reduction of body stiffness caused by lightweight,the fatigue failure problem of body structure occurs frequently.Therefore,how to identify the weak position of vehicle body structure in service at the early stage of design.At the same time,it is important to simulate the vehicle service conditions as accurately as possible so as to accurately evaluate the fatigue life of the key weak points of the vehicle body.In this thesis,combining the rigid and flexible coupling dynamics theory of vehicle system and the modal stress recovery method,the research on the dynamic weak position identification method of vehicle body is carried out,the research on the key position characteristic stress spectrum and the extrapolation method considering the characteristics of line and wheel and rail,as well as the life assessment of key parts based on the actual line conditions of beijing-guangzhou line.Work is as follows:Firstly,based on vehicle system dynamics,finite element theory and rigid and flexible coupling theory,the dynamic model of high frequency rigid and flexible coupling and vehicle body sweeping model are established.Based on the high frequency rigid-flexible coupling dynamic model of high-speed train,the influence of high frequency elastic vibration on vehicle dynamic performance index is analyzed.At the same time,the influence of modal cutoff frequency and damping ratio on vehicle system dynamic performance was investigated.The results show that the high frequency modes of the vehicle body are easily excited at high speed,which has a great influence on the dynamic performance of the vehicle.Large modal damping ratio can effectively suppress the modal vibration of the system.Therefore,the accuracy of the rigid-flexible coupling dynamics model is very important for the appropriate modal cutoff frequency and damping ratio.Secondly,the dynamic weak position(window Angle,door frame,pillow beam,traction beam and floor connection area,etc.)under the condition of vehicle body service was studied and identified by using the modal stress recovery method and the vehicle body sweeping model.These weak positions are more sensitive to the local modes of the frame sinking and floating,the first-order sag of the body,the rhombus of the body,the body torsion,the body underframe,the side wall and the roof.Based on the high frequency rigid flexible coupling dynamic model of high-speed train,the characteristic stress spectrum at the weak dynamic position of the train body is further studied.The results show that with the increase of vehicle operating speed,the decrease of curve radius and the increase of equivalent taper of tread,the modal vibration of vehicle body intensifies and the stress amplitude of dynamic weak position of vehicle body increases.The influence of curve radius and wheel-rail matching equivalent taper on characteristic stress spectrum distribution is studied by using three-parameter weibull distribution.Then,based on the actual line conditions of beijing-guangzhou railway,the dynamic weak position stress spectrum of the vehicle body under different wheel and rail matching equivalent taper is studied by using the high frequency rigid-flexible coupling dynamic model of high-speed train.In this thesis,the stress spectrum compilation method considering the equivalent taper evolution of wheel-rail matching is studied by non-parametric rain flow extrapolation method.The results show that the stress amplitude of the dynamic weak position of the vehicle body increases with the increase of the equivalent taper of wheel and rail matching.Considering the dynamic evolution of wheel-rail matching equivalent taper,the amplitude of the stress spectrum is larger than that if the equivalent taper is constant.Finally,based on the stress spectrum obtained by extrapolation,the fatigue life of high-speed train body at weak position is evaluated by using s-n curve of critical weak position.The results show that the fatigue damage calculated based on the stress spectrum of the dynamic evolution of the equivalent taper of wheel and rail matching is larger and more conservative than that obtained under the condition of constant equivalent taper of wheel and rail matching.