| In the process of train operation,rail or wheel vibration could be caused by wheel-rail irregularity and other reasons,which will directly affect the wheel-rail rolling contact fatigue damage and train operation safety and comfort.Therefore,the study on the rolling contact fatigue damage of rail under vibration condition has great scientific significance and engineering value to ensure the safety and reliability of wheel-rail system service.The rolling contact fatigue tests of rail was carried out using the MJP-30 A rail rolling wear and contact fatigue testing machine under the water condition.The effects of vibration amplitude and axle load on the rolling contact fatigue performance of rail were studied.The fatigue damage law was quantitatively characterized,and the fatigue crack damage mechanism of rail material under the vibration condition was revealed.The main conclusions of this thesis are as follows:(1)Compared with the condition without vibration,with the increase in vibration amplitude,the fluctuation amplitude of wheel-rail adhesion coefficient was increased under the vibration condition.With the increase in axle load,the fluctuation amplitude of adhesion coefficient was decreased gradually.With the increase in the number of cycles,the adhesion coefficient was changed slightly.There was no significant difference in the average adhesion coefficient between wheel and rail under both conditions(with and without vibration).(2)With the increase in the vibration amplitude,the thickness of plastic deformation layer was decreased,while the wear rate,surface damage degree,length and depth of fatigue cracks were increased slowly.When the amplitude was increased to 2100 N of the normal force,the thickness of plastic deformation layer was decreased greatly.The wear rate and surface damage were increased sharply,and the length,depth and density of fatigue cracks were decreased significantly.(3)When the axle load was smaller than or equal to 17 t,the rail surface damage mode was mainly slight spalling.With the increase in the axle load,the thickness of the plastic deformation layer was decreased,the fatigue damage of the surface was gradually intensified,and the average length and depth of the cracks were increased.When axle load was larger than or equal to 21 t,the rail damage was mainly characterized by severe spalling.The decreasing rate of plastic deformation layer thickness was accelerated,and the increasing rates of average length and depth of fatigue cracks on rail surface were accelerated.(4)With the increase in the number of cycles,the rail surface and subsurface fatigue crack damage was intensified.Under the same number of cycles,the surface and subsurface fatigue damage without vibration was milder than that under the vibration condition.When the number of cycles increased to 20,000 cycles,net-like cracks began to form.Compared with the condition without vibration,the density of net-like cracks was higher under the vibration condition.There was a certain angle deflection for the main crack when a branch crack was generated.(5)Compared with the condition without vibration,under the vibration condition,the surface hardening hardness was increased,the thickness of plastic deformation layer was decreased,the average tangential force and adhesion coefficient were similar,and the wear rate was increased.The propagation mode of cracks in the sample was mainly along the grain boundaries,and was supplemented by transgranular propagation.The numbers of branch cracks and transgranular propagation cracks were increased,and the fatigue damage of rail was aggravated. |
