Research On Fatigue Load Analysis And Life Prediction Of High Speed Switch Rail

High speed turnout is prone to fatigue damage under the cyclic action of complex alternating load.If improperly handled,the safe service performance of turnout will be seriously affected.Combined with the relevant research results of domestic and foreign scholars,this paper systematically studies the load characteristics of switch rail under the action of complex random parameters in actual operation,the fatigue sensitive area of turnout is also determined for life prediction.The specific work and conclusions of this paper are as follows:(1)The related research methods and theories of vehicle-turnout dynamics and fatigue damage analysis at home and abroad are systematically summarized.And the research significance of load characteristic analysis and fatigue life prediction of straight switch under complex random action is clarified.Meanwhile,the technical route of this paper is drawn up,and the appropriate research methods are selected.(2)Based on the multi-body dynamics software SIMPACK and the finite element software ANSYS,the vehicle-turnout coupled rigid and flexible model is established,the actual wheel-rail contact state and flexible deformation of turnout system are fully simulated.In addition,the load characteristics and vibration performance of the vehicle passing through No.18 high-speed turnout at 350 km/h speed are analyzed.The results show that all the dynamic indexes can satisfy the standard requirement when the vehicle crosses the turnout directly.For the case that the vehicle straight reverse passes through the turnout,the peak value of the wheel-rail vertical force is 127.13 k N,the peak value of the wheel-rail lateral force is 3.33 k N,the peak value of derailment coefficient is 0.06,the peak value of wheel unloading rate is 0.53,The peak value of vertical acceleration of vehicle body is 0.02 m/s~2,The peak value of lateral acceleration of vehicle body is 0.37 m/s~2,and the maximum vibration displacement of turnout sleeper is 1.52 mm.When the vehicle passes through the turnout in straight and forward direction,the wheel rail dynamic response and related dynamic indexes are relatively low.Only the wheel-rail lateral force and derailment coefficient are slightly higher than those in straight and reverse direction,which are 5.88 k N and 0.09,respectively.(3)The key dynamic parameters which have great influence on the load characteristics of turnout in the actual operation process are selected.Combined with the characteristics of parameters,random samples are obtained by using appropriate methods.The multi-dimensional sampling algorithm is used to compile the random simulation condition table to analyze the variation law of load characteristics of switch under complex random conditions.The results show that the change of turnout geometry,wheel-rail wear and key vehicle parameters will cause the change of load characteristics of straight switch rail in complex random conditions.The random irregularity excitation has the greatest influence on the dynamic response of the straight switch rail.The vertical load and vertical vibration displacement of the straight switch rail increase significantly,increasing by 39.63%and 32%respectively compared with the ideal state.The wheel-rail wear will cause the wheel rail force to fluctuate in a small range and delay the wheel load transition zone,while the key parameters of the vehicle have little effect on the change of the initial loading position.(4)Based on ANSYS finite element solid model,S-N curve and Miner linear accumulation rule,the fatigue damage analysis and life prediction of switch rail under complex random excitation are further carried out through multi load step stress cycle analysis.The fatigue sensitive zone of straight switch rail is related to the stress distribution characteristics and load cycle sequence of the structure.Under the standard working conditions,the fatigue sensitive zone of the straight switch rail is near the section with the top width of 37 mm,and the complex random excitation will lead to the change of the load sequence of the straight switch rail,which will delay the fatigue sensitive area to the section with the top width of 45 mm-55 mm.According to multi load step stress analysis and Miner linear fatigue damage accumulation of key section in turnout fatigue sensitive area,the fatigue life of straight switch rail is about 200 million tons under complex random conditions.