Study On Bending Fretting Fatigue Damage Behavior And Risk Assessment System Of EA4T Axle Steel

Fretting fatigue is common in automobile,rail transit,mechanical engineering equipment,aerospace and other fields.The occurrence of fretting fatigue will aggravate the damage of mechanical parts in contact,including the accelerated initiation and propagation of micro cracks,the increase of wear degree of contact area,and the significant reduction of service life of contact parts.As a key part of the running gear of railway passenger and freight vehicles,the axle plays a vital role in ensuring the safe operation of railway vehicles.To explore the bending fatigue fretting damage mechanism of EA4T axle material and study its risk assessment system have important reference and guiding significance for targeted protection of axle,prolonging service life of axle and improving safety performance of railway vehicles.In this thesis,the EA4T axle steel is taken as the research object,and the bending fretting fatigue test of EA4T axle steel is carried out with the 100 k N Shimadzu electro-hydraulic servo fatigue testing machine and the self-designed bending fretting fatigue test fixture.According to the test data,the S～N fatigue life curve of EA4T axle steel is constructed.Scanning electron microscope(SEM),energy dispersive spectrometer(EDS),electron probe micro-analyzer(EPMA)and white light interferometer(WLI)are used to systematically analyse the damage area of the samples and explore the damage mechanism.Then,the risk assessment system of bending fretting fatigue damage of EA4T axle steel is established based on analytic hierarchy process(AHP).The main conclusions are shown as following:(1)With the increase of fatigue load,the bending fretting fatigue life of EA4T axle steel firstly decreases,then increases,and abnormally decreases.The fretting region of bending fatigue S～N curve of EA4T axle steel can be divided into three parts: partial slip regime(PSR),mixed fretting regime(MFR)and slip regime(SR).The initiation and growth speed of micro crack in mixed fretting regime is fast,so the fatigue life of the sample in mixed fretting regime is the lowest;(2)In mixed fretting regime,the main crack appears in the contact area toward the loading end of fretting fatigue damage zone,and the secondary crack appears near the fixed end of main crack,while no crack appears near the loading end.This is because the deformation energy at the fixed end unable to release in time,and the plastic flow and plastic deformation unable develop to the right of the main crack due to the existence of the main crack;(3)The damage areas of EA4T axle steel bending fretting fatigue present asymmetric ellipse.The damage degree of the damage area near the loading end is the largest,followed by the fixed end,and the damage degree in the center of the contact area is the smallest.The fretting fatigue cracks usually initiate near the loading end.The wear volume,maximum wear depth and oxidation wear degree increase with the cycle times increasing;(4)Based on the analytic hierarchy process(AHP),the weight scores of partial slip region: 0.6491861,mixed fretting regime: 0.1365806,slip regime: 0.2042219,similar to the weight scores obtained by arithmetic average method and geometric average method.The minimum risk is partial slip regime,the slip regime is relatively high risk,and highest risk is the mixed fretting regime,which is consistent with the trend of EA4T axle steel bending fretting fatigue S～N curve.