Study On Wear And Damage Behaviors And Wear Prediction Of U75V Rail Under Dry And Water Medium Conditions

Railway rail,as the key core component of track structure,plays an important role in supporting and guiding the operation of trains.With the increase in axle-load and speed,the wear and damage behaviors of rail are complicated and changeable,which seriously affect the operation safety and reliability of trains.Therefore,in order to extend the service life and ensure the reliability of rails,the research on rolling wear and damage behaviors of rail is of great scientific significance and engineering value.The results can provide theoretical basis and technical support for guiding the scientific operation of rail service and material optimization in China.Based on the MJP-30A wheel-rail rolling wear and contact fatigue testing machine,wheel-rail rolling wear tests in dry and water medium conditions are carried out for U75V rail which is used in China railway lines.The effects of slip ratio,contact stress and water medium on the wear and damage behaviors of U75V rail are studied.The wear behavior of the counterpart wheel and the influence of friction white layer are analyzed.The wear diagram and damage mechanism diagram of U75V rail material are established,and the mechanism of microstructure plastic evolution of rail material is revealed.Based on the wear data,A Tγ/A-wear rate wear model of U75V rail material is established,and the wear behavior of U75V rail under different curve radii,train running parameters and third medium conditions is simulated and analyzed by using the dynamic model.The accuracy of the simulation results is verified by comparing with the on-site rail test results.The main conclusions of this thesis are as follows:（1）With the increase in slip ratio,the wear rate of rail increases,the hardness of rail and the thickness of plastic deformation layer increase first and then decrease,the surface damage changes from slight fatigue wear to slight adhesive wear and severe adhesive wear,and the fatigue crack propagation depth and angle increase first and then decrease.With the increase in contact stress,the wear rate increases when the slip difference is 3%and 12%.When the slip ratio is 25%,the rail wear rate increases first and then decreased with the increase in contact stress.The rail hardness and the plastic deformation layer thickness showe a trend of slight increase.The surface damage is aggreviated gradually.Specifically,the damge is changed gradually from peeling and fatigue crack into spalling,adhesion and oxidation.The rail fatigue crack propagation angle and depth are increased.（2）Compared with the dry condition,the wheel/rail adhesion coefficient,rail wear rate,plastic deformation layer thickness and surface hardening under water medium are smaller.With the increase in slip ratio,the wear of rail first decreases and then increases,the thickness of plastic deformation layer slightly decreases,and the angle and depth of fatigue crack increase obviously.With the increase in contact stress,the wear rate of rail does not change obviously when the slip difference is small,but increases when the slip difference is large.The plastic deformation thickness of rail increases with the increase in contact stress,and the fatigue crack size does not change obviously.With the increase in slip ratio and contact stress,the surface morphology of rail evolves from slight pitting and furrow to severe pitting and furrow until slight spalling.（3）The wear rate of wheel material increases slowly at first and then increases rapidly with the increase in slip ratio,and increases with the increase in contact stress.There is a positive linear correlation between the wear rate of wheel and that of rail.With the increase in slip ratio,the degree of wheel damage first increases and then decreases.The damage is aggravated with the increase in contact stress.The hardness of the friction white layer on the wheel surface is over 800HV_0.5.Compared with the samples without white layer,the wear amount of the wheel wheel white layer is significantly increased.The increase rate reaches200%.Rolling contact fatigue cracks are generated in both the white layer and the matrix,and the continuous propagation of surface cracks leads to material fragmentation and finally to spalling.（4）The U75V rail material wear map in dry condition can be divided into three areas:slight wear,severe wear and catastrophic wear.The main mechanism of rail damage in slight wear area is pitting corrosion,peeling,slight peeling and slight rolling contact fatigue.The main damage mechanism in severe wear area is severe spalling and rolling contact fatigue.The main damage mechanism in catastrophic wear area is that spalling pits and fatigue cracks are worn off,and large area of oxidation burning and furrows appear.The wear map of U75V rail material in water medium can be divided into two regions:extremely slight wear and slight wear.Rail material in dry state is more likely to slip in the area of catastrophic wear,while rail material in water state is more likely to slip in the area of extremely slight wear.After water enters the interface between wheel and rail,the tangential force decreases,and the material is less likely to slip along the tangential direction.The Tγ/A-wear rate wear model of U75V rail material in dry condition can be divided into three regions:（1）Tγ/A<14,Y=0.3+2.59*Tγ/A;（2）14≤Tγ/A<66,Y=34.02+0.16*Tγ/A;（3）Tγ/A≥66,Y=10.86*Tγ/A-672.18.（5）Based on the established U75V rail material Tγ/A-wear rate rate wear model,combined with the dynamic model,a rail wear prediction method is constructed,and the simulation analysis of the wear behavior of U75V rail under different working conditions is carried out.Comparing the simulation results with the field test results,it is found that the values of the two are basically consistent.With the increase in running speed,the wear depth of rail increases.When the running speed is less than 160 km/h,the wear speed increases slowly.The wear depth of rail increases linearly with the increase in train axl-load.The smaller the curve radius is,the more serious the wear of rail top and rail side is.Rail side lubrication can effectively reduce the side wear of rail,and the rail top FM friction control can reduce the wear of rail top to a certain extent.