Research On The Causes And Preventive Measures Of High-speed Railway Rails Squat

With the transition from the large-scale construction period to the operation period of my country’s high-speed railway,rail squat is more serious due to the relative sliding of the wheel and rail,and the long ramp that affects the traction/braking performance of the train is more prone to the relative sliding of the wheel and rail,which brings great challenges to the maintenance department.Therefore,it is of great significance to reveal the formation mechanism of rail squat in high-speed railway,and then to propose effective rail squat prevention measures to ensure driving safety and reduce maintenance and repair costs.This paper based on multi-body dynamics and finite element theory,a dynamic analysis model for high-speed railway rail squat was established,and the simulation analysis of the whole process of high-speed wheel-rail from adhesion state-large creep state-squat formation was realized.The change of wheel-rail adhesion characteristics of high-speed train running on long ramp was analyzed,and the causes of rail squat in highspeed railway were revealed.Identify the key factors that cause rail squat,on this basis,the preventive measures for rail squat are put forward according to the key factors that cause rail squat.The details are as follows:(1)Establish a dynamic simulation analysis model for rail squat in high-speed railway,including a vehicle-track macro-analysis model and a three-dimensional wheel-rail contact force-thermal coupled micro-analysis model.Based on the multi-body dynamics theory,a vehicle-track macro-dynamic analysis model is established,and is used to study the adhesion characteristics between the highspeed wheel and rail.Based on finite element theory,a three-dimensional wheel-rail contact force-thermal coupling mesoscopic analysis model is established,the model considers the plastic properties and temperature properties of wheel-rail materials,and is used to study the influence of different factors on the formation of rail squat under the state of large creep.(2)The changes of the adhesion characteristics of high-speed trains under the action of long ramps are studied.Based on the established vehicle-track macrodynamic analysis model considering the effect of the ramp,the train running speed,longitudinal creep force,the adhesion area of contact patch and the creep rate of the high-speed train are studied in the process of going up and down the slope.When the friction coefficient of the rail surface is constant,the train running acceleration,longitudinal creep force,and creep rate increase with the increase of the traction/braking coefficient,and the adhesion area of contact patch decreases with the increase of the traction/braking coefficient.When the rail contact patch begins to be in a state of full sliding,it can be judged that the train wheelset has idling/skidding.(3)The causes and main influencing factors of rail squat in high-speed railway are studied.Based on the established 3D wheel-rail contact force-thermal coupled mesoscopic analysis model,the effects of the train axle load,rail surface state,traction and braking states on the rail top surface force-thermal properties are studied.and the influence of the rail squat formation based on the force-thermal coupling mechanism of rail squat formation is discussed.The contact pressure of the wheel and rail presents a nearly ellipsoidal distribution,and the plastic zone on the rail surface is basically a long strip.When the creep rate increases to 40%,the maximum temperature rise of the rail under traction and braking conditions exceeds the phase transition temperature,resulting in squat on the top surface of the rail.(4)A rail scuffing prevention measure based on controlling the creep rate is proposed.Aiming at the key factors causing rail squat in high-speed railways,it is proposed to reduce the occurrence of rail squat by controlling the creep rate.The train traction/braking mode can control the creep rate below the threshold value of the creep rate that causes rail squat to achieve effective control of rail squat.