Study On Damage Tolerance Of Emu Hollow Axle Based On Vehicle System Dynamics

With the continuous increasing of the operating speed and the service time of EMU,the wheel/rail interaction tends to be more severe,and the wheelset axle is more likely subjected to external damage.This could lead to the formation of initial damage/crack on the axle.Due to the service loads,these cracks could propagate and result in the fatigue failure for the wheelset axle,which could significantly affect the operating safety of rail vehicle.Therefore,it is desirable to investigate the residual life of wheelset axle considering the service load conditions.In this thesis,the vehicle system dynamics and fracture mechanics were coupled to better characterize the stress intensity factors of wheelset axle,so as to estimate the damage tolerance of wheelset axle under the service load conditions.The following summarizes the main conclusions:(1)The service load of wheelset axle was investigated,and the deficiencies of the standard design load were analyzed.The results showed that the load on the axle could be divided into static load,low-frequency dynamic load and high-frequency dynamic load.The existing standard adopted an infinite life design based on quasi-static,only low-frequency dynamic loads were considered.To this end,a damage tolerance evaluation method of wheelset axle based on vehicle system dynamics was proposed to study the stress intensity factors and residual life of wheelset axle under the service load conditions.(2)The crack shape factor function was fitted,and a crack stress intensity factor calculation method based on dynamic loads obtained from simulation of vehicle system dynamic model was established.The results showed that the finite element method could be used to solve the stress intensity factor of wheelset axle,and the accuracy of the displacement extrapolation method was higher than that of the stress extrapolation method;considering the evolution characteristics of the crack shape,the crack shape factor function of wheelset axle under the rotating bending load and the press fitting load were obtained by fitting,the stress intensity factor of wheelset axle under dynamic rotary bending load was calculated.(3)The stress spectrum and stress intensity factor spectrum of the initial crack position of wheelset axle were studied,and the whole load spectrum based on the Wuhan-Guangzhou line conditions was compiled.The results showed that the change of vehicle speed had little influence on the maximum stress amplitude and the range of stress intensity factor corresponding to the maximum frequency;with the increasing of vehicle load,the decreasing of the super-elevation of the curve,the decreasing of the radius of the curve,the maximum stress amplitude and the range of stress intensity factor corresponding to the maximum frequency increased;with the increasing of the wheel polygon amplitude,the maximum stress amplitude and the range of stress intensity factor corresponding to the maximum frequency increased significantly.(4)The fatigue life of axle was evaluated based on the nominal stress method.The results showed that the vehicle load and curve radius had a significant influence on the damage of the initial crack position of the axle,and the polygonal wear of the wheel could significantly increase the damage of the axle;based on the load spectrum of the Wuhan-Guangzhou line,the fatigue life of the axle with and without the wear of wheel polygon was compared,it was found that the wheel polygonal wear could significantly increase the equivalent stress of the axle;however,considering the operating mileage of 15 million kilometers,the maximum damage of the axle was still far less than 0.3,indicating that the fatigue life of the axle has a large safety margin.(5)The residual life of axle was estimated based on the damage tolerance method.The results showed that the wheel-rail impact caused by wheel polygonal wear could significantly reduce the residual life of the axle in the case of cracks;when considering the initial crack depth of 1 mm,the residual life of the axle was reduced to 302000 kilometers from 2596000 kilometers in the case of wheel polygonal wear.The effects of initial crack depth,crack growth threshold and interference between the axle and wheel on the residual life of the axle were analyzed,and it was found that the initial crack depth and the crack growth threshold had a greater influence on the residual life of axle;with the increase of interference between the axle and wheel,the residual life of axle decreased gradually.