Effect Of Rail Weld Irregularities On Dynamic Stress Of Heavy-Haul Railway Fastening Spring Clip

The rail fastenings are important components of the track structure, which are intended for clamping down the rail at the right position, preventing the rail from moving in the lateral and longitudinal direction, bearing and transferring the longitudinal, the vertical as well as the lateral train forces, and providing a certain degree of elasticity for the track. In recent years, track structure damage becomes more serious due to the continuous rapid increase of the axle load, the traffic density, the operating speed as well as the traction load of freight train, which cause the track load conditions to become worse and worse. Thereinto, a number of fatigue damage, even broken of the fastening clip appears caused by rail weld irregularities. Against the background of heavy haul railway development, this thesis aimed at the spring clip type II fastening widely used on Chinese heavy haul railways, analyzed the fastening clip dynamic stress and the fatigue life using the finite element method and the vehicle-track coupled dynamic theory.Based on the nonlinear contact theory, a detailed finite element analysis model of the rail fastening system including the plain washer, the spring clip, the gauge apron and the insulated block had been established. Mechanical characteristics of the fastening clip under different preload pressure were studied with the finite element model. When the fastening is installed in the right place, the fastening clip’s von Mises stress and stress distribution on the cross-section were analyzed. The results show that the fastening system will complete the installation when the preload force reaches 25kN, the clamping force of fastening clip is 10.2kN and the vertical displacement of the fastening clip middle part is 10.7mm, which satisfy the design requirements of the spring clip type II fastening. Besides, there exits slight local plastic yields located in the 0.4mm-depth surface layer of the rear bent parts, this phenomena are consistent with the engineering practical experiences. This indicates the FEM can reflect accurately the fastening clip stress and strain status.Dynamic loads of the fastening system excited by rail weld irregularities were calculated using the vehicle-track coupled dynamic theory and its method, dynamic stresses and vertical displacements response of the fastening clip were analyzed. Numerical results indicate that the running speed of freight train has little influence on the fastening clip dynamic stresses and vertical displacements under ideal smooth track condition, and the axle load is the main factor affecting spring clip stresses. If there exits rail weld irregularities, both dynamic stresses and vertical displacements of the fastening clip increase with the increase of the axle load and the running speed of the train. When the wheelset passes the rail weld irregularities, the von Mises stress amplitude and the vertical displacement of the fastening clip have little change with the growth of the axle load, but increase rapidly with the growth of vehicle speed. At the condition which wave depth is the same, the amplitude of the von Mises stress and the vertical displacement of the fastening clip as well as their sudden change value increase rapidly as the wave length decreases, the dramatic increase of the fastening clip’s von Mises stress when wave length smaller than 0.2m. At the condition which wave length is the same, the amplitude of the von Mises stress and the vertical displacement of the fastening clip as well as their sudden change value increase linearly with the growth of the wave depth when the wheelset passing rail weld irregularities.Based on the result of statics and dynamics calculations of the fastening clip, the fatigue life of the fastening clip under the excitation of constant amplitude load and rail weld irregularities were analyzed. The results show that the fatigue life of the fastening clip type II satisfies the requirement of 5 million times under specific load condition according to the fatigue test standard. The fatigue life of the fastening spring clip decreases with the growth of the axle load, the running speed and rail weld irregularity wave depth and increases with the growth of the irregularity wave length when there exits rail weld irregularities. In addition, the high stress amplitude caused by the axle load and rail weld irregularity plays a dominant role in the fatigue life of the fastening clip.