Study On Bending Fretting Fatigue Damage Of 15-5PH Martensitic Precipitation Hardening Stainless Steel

Fretting fatigue is widespread in various "fastening" joints in the fields of machinery,transportation,electric power,military industry,aerospace,nuclear reactors and even biomedicine.Fretting fatigue will significantly reduce the service life of mechanical components,resulting in premature failure.Due to its excellent performance,15-5PH stainless steel is widely used in important fields such as aerospace,military industry,marine industry,and nuclear industry.Therefore,the fatigue test of 15-5PH stainless steel is of great engineering practical significance for the anti-fatigue design of the material and the improvement of its service performance.In this research,by means of a self-designed bending fretting fatigue test rig,we focused on 15-5PH stainless steel,which is the main material of aerospace spline shaft,and systematically investigated the bending fretting fatigue S～N curves and the bending fretting fatigue life characteristic curves.Moreover,a detailed microscopic analysis on the damage area of all tested samples was performed by a combination of the optical microscope(OM),scanning electron microscope(SEM),residual stress analyzer,white light interferometer(WLI),energy spectrometer(EDS)and electron probe microscope analyzer(EPMA).Lastly,the bending fretting fatigue damage mechanism of 15-5PH stainless steel was systematically explored and proposed.The main conclusions are summarized below:(1)The bending fretting fatigue life of 15-5PH stainless steel was much lower than that of conventional bending fatigue life,and its bending fretting fatigue S～N curve presents a inclined "Z" curve characteristic.This indicates that the bending fretting fatigue life of this material varies with the fatigue load gradually increasing,it first decreases,then abnormal increases,and finally shows decreasing trend.As the fatigue load increases,the fretting runs in the partial slip regime(PSR),mixed fretting regime(MFR)and slip regime(SR)in sequence;(2)After the test,the surface residual stress of 15-5PH stainless steel sample on both sides of the fretting contact area presents a similar "bell" trend.The surface residual tensile stress gradually decreases with the increase of the distance from the fretting contact area,and finally transits to the compressive stress.At the same distance from the fretting contact area,the surface residual tensile stress near the loading end is always larger than that at the fixed end;(3)The overall damage morphology of the contact area in bending fretting fatigue is an asymmetrical ellipse.The damage is the severest at the loading end,followed by the fixed end,and the center of the contact area is the mildest.The crack source nucleates in the damage area toward to the loading end on the contact area.The crack source nucleated on the subsurface of the damage zone,which was about 50μm ～ 100μm from the loading end.According to the different effects of normal contact stress and bending fatigue stress on the crack initiation and propagation,the crack initiation and propagation were divided into three stages,and finally resulted in the fracture failure of the specimen;(4)As the normal load increases,the bending fretting fatigue life of 15-5PH stainless steel shows a trend of first decreasing,then increasing,and finally becoming stable.The normal load has a negligible effect on the oxidation degree of the contact damage zone.And the influences of normal load on the bending fretting fatigue life of the material are mainly ascribed to the plastic deformation,stress concentration and the degree of wear between the fretting pad and specimen.