Research On Rail Contact Fatigue Crack Initiation Life Considering Stochastic Factor

With the rapid development of heavy-haul railway in China,the rail contact fatigue damage becomes more and more serious,which increases the maintenance cost.Rail rolling contact fatigue damage is one of the main types of rail damage in heavy-haul railway.The research on the initiation and propagation mechanism of rail rolling contact fatigue crack will provide a theoretical basis for mitigating rolling contact fatigue damage.In the actual situation,fatigue crack initiation life is affected by many factors which are often random.Only when the randomness of factors is fully considered,can the prediction of fatigue crack initiation life of the rail be more reasonable and effective.Considering the randomness of the factors,the cumulative fatigue damage of rail is studied.Firstly,a three-dimensional wheel-rail contact finite element model is established by using the finite element theory.In view of the wheel-rail contact position,wheel load,friction coefficient on the surface of the rail,temperature stress,the longitudinal stiffness of the track,lateral stiffness of the track,a scheme is established by means of cross orthogonal test method to analyse the effect of these factors to fatigue crack initiation life of the rail.According to the study: the contact position of wheel and rail,wheel load,the friction coefficient of the surface of the rail are the significant factors of the fatigue crack initiation life of the rail.The influence of wheel-rail contact position and wheel load on the fatigue crack initiation life of the rail is analyzed.Research shows that: when the wheel load doesn’t change but wheel-rail contact position changes,the fatigue crack initiation life of the rail is mainly influenced by the shape of wheel-rail contact patch and the wheel-rail contact area;When the wheel load changes but wheel-rail contact position doesn’t change,the fatigue crack initiation life of the rail has a great correlation with the normal contact stress of wheel-rail.The greater the normal contact stress of wheel-rail,the shorter the fatigue crack initiation life of the rail.When the sliding area in the wheel-rail contact patch increases,the fatigue crack initiation life of the rail would be longer.Finally,considering the randomness of wheel-rail contact position and wheel load,a prediction model of the fatigue crack initiation life of the rail under random parameters was established based on the critical plane method and the Miner theorem.Research suggests that: when the reliability is 50%,the fatigue crack initial life of rail considering multiple random factors is 47 680 times;For each point of the rail head,there are 2 angular regions with serious fatigue damage.On the plane corresponding to the angle of the angular region,the fatigue damage changes continuously;According to the statistics of the critical plane of all the points of the rail head,the angle between the these critical planes and the longitudinal cross section of rail and the angle between these cants and the surface of the rail are not almost distributed in a certain Angle range,but the angle between these critical planes and the rail cross-section are mainly distributed in the range of 55° ~ 114°;The more frequently the wheel-rail contact position appears within a certain range,the more serious the fatigue damage will be in these positions.