Research On The Nonlinear Characteristics Of A New Mesh-type Rail Pad And Its Influence On Dynamic Performance Of Wheel-rail System

Ballastless track is widely used in high-speed railway in China,and the elasticity of track structure is mainly provided by fastening system.Fastener system plays an important role in rail fastening,reasonable rigidity providing,line resistance,etc.The stiffness and damping of the fastener system are provided by the elastic rail pad,which is closely related to the running stability,safety and the long-term maintenance of the healthy service capacity of the track structure.Therefore,it is significance for the design and maintenance of high-speed railway in China to optimize the structure of elastic rail pads and analyze its dynamic performance.The main contents of this paper are as follows:(1)A new type of mesh elastic pad structure is proposed.In this paper,the threedimensional finite element model of mesh type elastic pad is established,and Mooney-Rivlin hyperelastic model is selected to simulate the characteristics of rubber material.Under the condition of constant parameters material of elastic pad,the effects of key geometric parameters such as mesh spacing,mesh diameter,plate thickness and chamfer radius on the static stiffness of mesh type elastic pad are studied,and compared with the traditional groove type elastic pad.The results show that the maximum stress of the mesh type elastic pad is obviously reduced compared with the traditional groove type elastic pad with similar static stiffness,which effectively improves its durability.At the same time,the static stiffness of the mesh type elastic pad would be flexibly adjusted by changing the mesh spacing,mesh diameter and plate thickness.Therefore,it is feasible to apply the mesh structure to the railway fastener system.(2)The temperature variation characteristics of dynamic stiffness and damping coefficient of mesh type elastic pad in extremely cold environment are studied in this paper.Based on the vehicle-track coupling dynamics theory,the driving safety and stability of the mesh type elastic pad under the extremely cold condition are studied,and the applicability of the mesh type elastic pad in the extremely cold environment is evaluated.The results show that the wheel/rail force and wheel load reduction rate increase significantly with the decrease of environment temperature and the vertical displacement of rail decreases with the decrease of temperature.In extremely cold environment,the wheel load reduction rate of high-speed train increases sharply.In order to ensure the safety of train operation,the train operation speed should be reduced.(3)In order to study the influence of the nonlinear stiffness amplitude of the mesh type elastic rail pad on the dynamic response of the interaction between the vehicle and the track system,the displacement-load curve of the mesh type elastic pad is measured by the SUNS fatigue testing machine.The nonlinear stiffness expression of the pad is fitted by the least square method.Based on the coupling model of high-speed railway vehicle-ballastless track,the influence of the linear stiffness and nonlinear stiffness of the mesh type elastic pad on the wheel/rail force,vehicle body vibration acceleration,rail vibration acceleration and other indicators is studied.The results show that: after linearizing the stiffness,the wheel/rail force and rail vibration acceleration will be overestimated in the middle and low frequency segment,while the wheel/rail force and rail vibration acceleration will be underestimated in the middle and high frequency segment;the linearity of the pad stiffness has little impact on the vehicle vibration acceleration.(4)The nonlinear behavior of a new mesh-type elastic pad under the influence of dynamic frequency and amplitude is studied.The fractional derivative viscoelastic element(FDV)is used to simulate the frequency dependence of the new mesh-type elastic pad,and the friction element is used to characterize the amplitude dependence.The frequency and amplitude dependent parameters of the proposed pad were measured.Temperature factor and MooneyRivlin strain energy density were introduced to simulate the mechanical properties of rubber materials at low environment temperature.Based on the coupled dynamics theory of vehicleslab ballastless track,the influence of the amplitude/frequency dependence of mesh type elastic pad on the dynamics of vehicle-track system in extremely cold environment is studied.The results show that with the increase of frequency,the dynamic stiffness and damping coefficient of mesh type elastic pad increase.Considering the temperature,frequency and the amplitude dependence,mesh type elastic pad model predicts the dynamic response of vehicle-slab ballastless track system under random irregularity and polygonal wheel excitation more accurately.