Study On Wear Behavior And Debris Particles Emission Characteristics Induced By Wheel-rail Rolling Contact Under Frequent Start-stop Conditions

Wheel/rail as the key foundation of rail transit vehicles running parts,is shouldering the load traction,braking and other important functions,thus to effectively evaluatead adhesion and wear wheel/rail relationship to the economy and safety of rail transportation is of great importance.With the development of modern rail transit,the speed of train is increasing.High acceleration and high deceleration when the vehicles enter and exit the platform are the inevitable choice to further improve the operating speed.Fast start and stop,short station distance and low noise have become the inevitable trend of the development of modern rail transit.Damage of wheel/rail interface is also growing.Compared with constant speed operation,the rolling contact stress at the wheel-rail interface becomes more complex due to acceleration/deceleration during frequent Start-Stop Conditions.At the same time,the emission characteristics of the debris particles are not fully understood.Therefore,study on wear behavior and debris particles emission characteristics induced by wheel-rail rolling contact under frequent start-stop conditions has become one of scientific problems needed to resolve in wheel/rail relations.Using the JD-DRCF/M wheel/rail rolling contact fatigue wear test rig,studied under different accelerations the wheel/rail rolling contact behavior between,and real-time monitoring the particulate emission characteristic of the wheel/rail interface;Then,the optical microscope was used to observe the microstructure,fatigue crack and plastic deformation.Scanning electron microscope（SEM）was used to observe the surface morphology of wear mark,and X ray energy spectrum（EDS）was used to analyze the element distribution on the worn surface.The three-dimensional morphology of wear marks was measured by optical three-dimensional profilometer.At the same time,combining with ABAQUS finite element simulation,the stress and strain behaviors of the wheel-rail interface with different frequent start-stop conditions were analyzed,and the rolling contact wear behavior of the wheel-rail interface under frequent start-stop conditions was further revealed.The main conclusions of this paper are as follows:（1）The wheel-rail rolling contact wear behavior under frequent start-stop conditions with different accelerations was studied.The results show that the adhesive coefficient between wheel/rail is affected by acceleration significantly;Accelerated phase is completed,with the increase of the acceleration adhesive coefficient in turn down before rising trends;At 800r·min^-2 acceleration,the adhesion coefficient shows the minimum value,which is about0.44,less than 70%of that under the condition of no acceleration.（2）Acceleration also has significant influence on the interfacial wear of wheel/rail,but the influence law is different.The wheel-rail wear is closely related to the shear stress at the wheel-rail interface,and moderate acceleration(a_r=800 r·min^-2)can slow down the wheel-rail wear.Frequent start-stop conditions have strong interference effect on the formation mechanism of wear debris.Under the condition of no acceleration,the wear surface is easy to accumulate oxidized wear debris.Combined with finite element analysis shows that in the process of acceleration of wheel/rail interface contact area S-Mise stress,cyclic shear stress increased,and the acceleration increases.Therefore,it will lead to fresh substrate is more exposed,and the wear debris is not easy to accumulate and can not be oxidized in time,and the characteristics of spalling are prominent.Therefore,when no acceleration and acceleration is small,the wheel/rail surface accumulation of wear debris had antifriction effect;When vibration acceleration,wheel/rail peeling layers increase,surface is uneven,spalling characteristics significantly,he acceleration of ascension will aggravate wheel surface damage and wear mechanism of transition from mild wear to severe wear.（3）With the increase of the acceleration,the wheel plastic deformation layer thickness increases gradually,and rail plastic deformation layer thickness basic remain unchanged.According to the finite element analysis shows that the plastic accumulation increases under the influence of acceleration.Under the condition of no acceleration,the crack only appears on the surface of the material with finite cycles,and no obvious crack propagation phenomenon is found.Under the condition of acceleration,the subsurface cracks are initiated under the action of alternating stress,and the surface cracks propagate downward.When the crack propagation process,the part of the crack forming crack.After the crack meets the subsurface crack,it will expand along the ferrite line to the surface in the plastic deformation area.When it reaches the surface,it will form a larger crack.After a period of test,the material above the crack will be broken by fatigue and fall off in the form of abrasive debris.（4）Under the stable operating condition without acceleration,the wear debris is relatively loose and mainly granular.The proportion of large particles（50μm to 100μm）is much lower than that of acceleration condition,but the emission of small particles（d≤1.0μm）is higher than that of acceleration condition.Under the acceleration condition,the debris flakiness characteristic is obvious,and the large particles（50μm to 100μm）are the most at800 r·min^-2 acceleration,and the size is relatively uniform.The start and stop conditions（acceleration）significantly increased the particulate matter（3.0≤d≤10.0μm）of emission of,especially at lower accelerations(400 r·min^-2).