Research On Crashworthiness Of High Speed Train Axles Under Impact Of Foreign Objects

Axle is an important running component in a train.With the continuous expansion of high-speed train operation areas and improvement of operating speed in China,requirements for impact resistance of axles are becoming higher and higher.During the service process of high-speed trains,it is difficult to avoid damage caused by impact of foreign objects on the track,such as scratches,plastic deformation,and impact craters,which may result in a reduced fatigue strength of axles.Typical foreign objects mainly include metal objects falling from the bottom of the train and ballast rolled up from the track.Coating protection is an important way of axle protection.It achieves impact and corrosion protection on the axle by coating the axle surface with a certain thickness of paint.However,some axles may experience coating loosening after a certain period of operation,resulting in a reduction in the impact resistance of the axles.Therefore,it is of great significance to study the impact damage laws and mechanisms of high-speed train axles under different operating conditions.At the same time,the study of the interface stress between coating and axle under different load conditions can provide a guidance for improving the protection performance and reliability of the coating.Based on numerical simulations,this paper studied the effects of two typical foreign objects,metal objects and ballast,on the impact damage of an uncoated axle of high-speed train under different conditions.For comparison,computational models for the impact of ballast on the axle with polyurea coating protection were established to study the effects of ballast size,impact speed,and coating thickness on the impact damage of the axle.At the same time,the effects of running speed,temperature,and coating thickness on the interfacial stress between the axle and the surface coating were studied.In order to deepen the understanding of the loosening mechanism of axle protection coating and provide a theoretical basis for the design of the axle impact resistant coating.The specific work is detailed below:First,computational models for the impact of steel balls on axle material samples were established,numerical simulations are conducted to obtain the diameter and depth of impact pits formed on the surface of axle material samples.The parameters of the constitutive model of axle material are determined and verified by comparing the simulated results with the experiment ones in the literature.On this basis,computational models for the impact of metal objects on the axle of high-speed trains were established,and the effects of the shape,size,impact speed,and impact angle of metal objects on the impact damage of the axles are analyzed.The research results show that the vertical collision of a metal object with an angle of 90~o between the center line of the axle is the most dangerous situation during high-speed train operation,and it can be found that the tetrahedral metal object has more severe impact damage on the axle surface than the corresponding spherical metal object,and the maximum impact crater depth that can be formed on the axle is about 3.15 mm.Second,based on calculation models of high-speed train axle impacted by metal foreign objects,considering that typical foreign objects are ballast,it uses SPH particle discretization.Computational models for the impact of ballast on an axle of a high-speed train were established,and the effects of the shape,size,and impact speed of the ballast on the impact damage of the axle are analyzed.The research results show that at the same speed,the impact damage of regular tetrahedral ballast on the axle surface is more severe than that of corresponding spherical ballast,and the maximum impact crater depth that can be formed on the axle is about 0.5 mm.Third,in order to study the protective effect of the coating,calculation models for high-speed train axle with polyurea protection coatings subjected to ballast impact were established,and the effects of ballast size,impact speed,and coating thickness on axle impact damage were analyzed.The research results show that the impact resistance of axle with a certain thickness of coating protection is significantly improved,with a 4 mm polyurea coating improving the impact resistance of axles by about 74%,and a 5 mm and 6 mm polyurea coating improving the impact resistance of axles by about 87%and 90%,respectively.Within the range of parameters studied,the difference in protective performance between 5 mm and 6 mm polyurea coatings is not significant,but it is significantly better than the protective performance of 4 mm polyurea coatings.Fourth,in order to study the variation of interface stress between coating and axle under centrifugal load,thermal load and coupling,a computational model for a high-speed train axle with a polyurea coating on its surface was established,and the effects of operating speed,temperature,and coating thickness on the interfacial stress were analyzed.The results show that within the range of parameters studied,the interfacial tensile stress caused by centrifugal load is relatively small,not exceeding 0.2 MPa.The interfacial stress caused by thermal load is very significant.When the temperature is-20 ~oC,the interfacial tensile stress reaches about7 MPa,which poses a significant hazard to the peeling off of the coating.Under the coupling of centrifugal load and thermal load,the influence of thermal load is dominant,and the total interfacial stress will be higher than the sum of the interfacial stresses acting alone.