Analysis On Turning Surface Texture Of Wheel-axle And Experimental Study On Fatigue Property

In the operation of high-speed railway,the fatigue damage of the axle is the main cause of the accident.The surface roughness of the axle and the crack affect the fatigue life of the axle.Therefore,it is necessary to improve the surface machining quality.During the fatigue test of the wheel set parts of the EMU,the transition arc of the wheel seat and the wheel seat is cracked.Because of the long process of the test wheel production from the axle,wheel set to wheel set,there are many influencing factors.In order to find out the cause of the crack in the condition of wheelset press fatigue test,the influence of the surface texture of the axle on the fatigue performance was analyzed from the beginning of the axle production.Firstly,the key parts of the surface of the current production of EA4 T axle are conducted on roughness test,residual stress test.Using optical microscope and scanning electron microscope,surface texture and surface structure of the key parts of the axle are conducted on observation and comparison;then machining four different process turning specimen with the roughness within 0.8?m four types of samples,the roughness and residual stress of them are measured.Conducting on rotating bending fatigue test,the fatigue life will be obtained.Then analyse fracture?near fracture surface texture and surface microstructure.At last,analyse the reasons of fatigue fracture.The results show that the surface texture is more regular,the turning quality is high,the surface of the majority of turning marks straight,smooth and evenly distributed,every two deep turning marks have a uniform distance,a few areas of the turning marks have burr,turning sticking wear and material peeling.The surface of the axle of the two materials has a layer of uniform fine crystal layer,the number of granular cementite gradually decreases from the inside to the outside,the surface fine grain layer is almost no granular carbide;ferrite of the sub-size gradually reduces from the inside to outside.ER8 wheel from the surface to the heart can be divided into:fine crystal area,transition zone,fibrous deformation zone and substrate.Increasing the axle speed,or reducing the depth of cutting,can reduce the sample surface roughness.The axial residual stresses of the four kinds of turning processes are compressive stresses,and the circumferential residual stresses are tensile stresses.When the turning depth and feed rate remain unchanged,the axle speed increases,the specimen surface axial residual stress decreases,while the circumferential tensile stress increases slightly.When the axle speed and feed rate remain unchanged,increasing the depth of the cutting,the specimen surface axial residual stress increases,the circumferential residual tensile stress decreases.Under the condition of satisfying the surface roughness of the sample within 0.8?m,the influence of the turning process parameters on the fatigue life of the axle specimen is not significant(2.9%).The fatigue crack source of the axle turning specimen is sprouted and expanded inward at the root of the surface deep turning marks.