The Effect Of Grinding Marks On Contact Fatigue Damage Of Rail Materials Under The Water And Oil Medium Conditions

Rail grinding use the high-speed rotating grindstone installed on the grinding train to remove the rail surface material.The grinding stone used for grinding is composed of one grain of abrasive grains.The process of rotating the grinding stone to remove the mater ial is a single grinding process.After rail grinding,the rail surface will leave a large number of visible grinding marks.It makes the the rail surface very uneven,and stress concentration will tend to occur during the service process,which affects the the rail service life.When there is a third medium such as water and oil on the rail face,the grinding marks make the pressure distribution extremely uneven between the contact surfaces of the wheel and rail,which greatly accelerates the rails fatigue failure.Therefore,studying the effect of grinding marks has important reference significance for the quality control of grinding rails.A MMS-2A wheel/rail friction wear testing apparatus was used to carry out experiments on rolling contact fatigue dama ge of rail materials with the rail grinding marks.Based on various instruments in the laboratory: roughness profiler,Vickers hardness tester,optical microscope,scanning electron microscopy,etc.,the paper analyzes the rail grinding marks parameters that affect the contact fatigue damage of rail materials,and elaborates the differences and disciplines of contact fatigue damage of rail materials caused by rail grinding marks parameters.The main conclusions of the paper are as follows:(1)Under the dry conditions,the rail grinding marks will wear quickly,and it has little effect on the contact fatigue damage of the rail material in the subsequent operation.The rail grinding marks in different directions do not have significant contact fatigue damage to the rail material.(2)Under the oil medium,severe spalling pits appear on the rail specimens surface which the end of grinding marks with the angle of 0°,45° to the running direction.And the profile cracks in the area are also very serious.In the area where the grinding marks with the angle of 90° to the running direction,the damage perpendicular to grinding marks on the surface of rail specimen,but the damage is more slight than the 0° and 45° grinding marks area.And the end of the grinding marks on the rail specimens surface,the spalling pits and profile cracks are very slight.(3)When there is water medium during the running of the wheel-rail specimen,The grinding marks with the angle of 0° ~ 45° to the running direction can accelerate the fatigue cracks propagation compared with the smooth area on rail specimen without prefabricated grinding marks.And the crack propagation is particularly serious on the rail specimen surface with the angle of 20° grinding marks which has a lot of branch cracks.The growth of the fatigue cracks slows down for the rail specimen with the grinding marks angle of 70°,90°,and there are only surface cracks on the rail specimen with the angle of 90° grinding marks(4)Under the water medium condition,the influence of grinding marks roughness is the same on the contact fatigue damage of the rail when the angle between the grinding marks and running direction is 0°,20° and 90°.As the roughness increases,damage is reduced(5)When there are grinding cross marks on the surface of the rail face,the flow of water medium is more disordered in the grinding marks,so the contact fatigue damage is less severe to the area of the single direction grinding marks.