Numercial Analysis Of Wheel/Rail Adhesion Characteristics Considering The Roughness Of Contact Surface

Wheel/Rail contact is the most important contact pair in rail transport system.With the rapid development of high-speed railways inland,the wear of wheels and rails has become worse,and the problem of low adhesion has become more frequent.Controlling wheel-rail adhesion is a guarantee for safe driving and normal operation of the railway.At present,there are not too many researches on wheel-rail adhesion based on rough surface contact at home and abroad;and with the increase of running speed,Coulomb's friction law is more difficult to describe the rolling motion between wheel and rail.Traditional numerical methods assume ideally smooth contact geometry between rail and wheel,namely neglecting surface roughness,and apply Coulomb friction law to every point within the contact patch.Therefore,it is necessary to study the wheel-rail adhesion characteristics of roughness from the perspective of theoretical and numerical simulation.Based on the roughness of the actual wheel and rail surface,this paper uses the Matlab program to generate rough wheel and rail surfaces that are in contact with each other.Through the correction of the Hertz contact theory on the vertical contact,the redistribution of the vertical stress on the pair of the asperity contacted in actual is obtained,and the wheelrail vertical stress distribution considering the roughness is obtained.The elastoplastic contact of the asperity is simulated based on the dynamic friction model and the molecular dynamics on the tangential contact,from the establishment of the contact to the stretching,to the necking to the fracture and the short interval of each microprotrusion contact pair After re-establishing the entire life cycle.A multi-scale wheel-rail adhesion numerical analysis model from micrometer scale to meter scale is established.The main contents and conclusions are as follows:1)Through the comparison of the results of numerical simulation with the indoor wheelto-roller test data and the outdoor test data,it is found that no matter on high speed or low speed,the traction coefficient-creep rate curve of the model can be highly consistent with the test data,which verifies the validity of the model.2)Analyzing of influence of the parameters in the model,get the conclusion how these parameters work on adhesive properties between wheel and rail.Ratio of contour contact area,micro-convex ellipsoid long-axis ratio and tangential contact stiffness coefficient do not change the value of the adhesion coefficient.However,interval time and maximum static friction coefficient of the joint can directly change the value of adhesion coefficient.3)On dry condition,the traction coefficient increases linearly with the increase of the longitudinal creep rate,then slowly increases to the maximum value and starts to decrease;the speed has little effect on the adhesion coefficient;the adhesion coefficient decrease a little with the increase of the axial weight;the wheel diameter does not change the value of the adhesion coefficient.4)The model reproduces the adhesive sliding changing process in which the friction coefficient gradually increases from zero to the maximum static friction coefficient and then decreases to the dynamic friction coefficient.The sliding area and the adhesion area in the contact spot no longer have a clear boundary.