On the damage mechanisms of bending fretting fatigue

TribologyInternational76(2014)133–141

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TribologyInternational

journalhomepage:http://www.77cn.com.cn/locate/triboint

Onthedamagemechanismsofbendingfrettingfatigue

J.F.Peng,M.H.Zhun,Z.B.Cai,J.H.Liu,K.C.Zuo,C.Song,W.J.Wang

TribologyResearchInstitute,TractionPowerStateKeyLaboratory,SouthwestJiaotongUniversity,Chengdu610031,China

articleinfo

Articlehistory:

Received8July2013Receivedinrevisedform22December2013

Accepted28December2013

Availableonline18January2014Keywords:

FrettingfatigueBendingfrettingDamagemechanismDislocation

abstract

Thebendingfrettingfatiguetestsof316Lausteniticstainlesssteel,7075aluminumalloy,LZ50steeland30CrNiMo8steelhavebeencarriedoutunderdifferentbendingstressesandnormalcontactstresses.TheS–Ncurvesofvariedmaterialsaresetupaccordingly,whichpresenttheshapeliketheGreekletter“ε”andcanbedividedintothreerunningregimessimilartofrettingwear.BasedontheOM,SEM,EDSandTEM,thefrettingfatiguedamageshavebeenanalyzedindetail.Thefrettingweardamagemechanismsoffrettingzoneareabrasivewear,oxidativewearanddelamination,adamagephysicalmodelintheMFRisproposed.AccordingtotheTEMresults,twocrackinitiationmechanismshavebeenproposedbasedondifferentmaterialcharacteristics.

&2014ElsevierLtd.Allrightsreserved.

1.Introduction

Frettingisthesmall-amplitudeoscillatorymovementwhichmayoccurbetweencontactingsurfaces[1],andmayleadtosurfacedamage[2–4],whichwas rstreportedintheopenliteratureaboutonecenturyago[5].Frettingresearchiscomposedbyfrettingwear,frettingfatigueandfrettingcorrosion.Asarule,frettingfatiguefailureresultsfromcrackformationandpropaga-tioninacomponentunderthecombinedactionoftwofactors:(a)thetotalcyclicstressonthecomponentand(b)thelocalstressarisingfromtherelativeslipofthesurfacesofthetwoelementsincontactunderthepressure.Contactstressesresultingfromsurfacefrettingcandramaticallyreducethefatiguestrengthofacompo-nentascomparedtothesamecomponentsustainingonlythebulkfatigueloads[6–12].Accordingtothemodesofbodycyclicstress,thefrettingfatiguecanbedividedintothreesampletypes,i.e.tension–compression(ortension–tension)frettingfatigue,bend-ingfrettingfatigueandtorsionalfrettingfatigue,asshowninFig.1.Therearemanyresearchmainlyfocusedontheprioritymodeuptothepresent;however,thestudiesonthetwolattermodesarestillinsuf cient,especiallyonbendingfrettingfatigue[6–10].

Thebendingfrettingfatiguecanbede nedasthedamageistheconsequenceofacyclicbendingloadimposedtothecontact-ingcomponentstoshortenthefatiguestrengthofthecomponentsearly,wheretherelativemovementoffrettingisresultedfromthecyclicalbendingstress.Failurephenomenaofbendingfrettingfatiguebroadlyoccurinthemodernindustrial elds,suchas

electricalmotorshaftandpinionshaftofmotors,dovetailgroovematchinginturbineengines,overheadelectricalwires,andothershrink- ttedcomponents.However,morestudiesextensivelyfocusedonthewheel-on-axleassembly,especiallyaxlesofrailwayvehicles[3–5].

Manyresearchershaveinvestigatedthetension–compressionortension–tensionfrettingfatiguewidely[11–16];however,themechanismsofbendingfrettingfatiguearestillnotclearnow,soitisnecessarytosystematicallystudythebendingfrettingfatigue.Ontheotherhand,inordertoenhancethereliabilityandtheservicelifeofcomponents,thedamagebehaviorsoffrettingfatigueunderbendingconditionsarealsoworthtostudy.Inthepreviousworksoftheauthors0group,thebehaviorsofbendingfrettingfatigueofmediumcarbonsteel(LZ50steel[8]),aluminumalloy(7075[10])andstainlesssteel(316Lsteel[9])havebeeninvestigatedindetail.Recently,otherdifferentsteels(30CrNiMo8and17CrNiMo6alloysteels)havebeeninvestigatedunderthesameconditions.Thus,inthispaper,themechanismsofbendingfrettingfatigueareoutlinedaccordingtotheresultsobtainedfromthevariedmaterials.

2.BendingfrettingfatiguetestersandtestparametersOnahydraulicservofatiguetestmachine,throughthenewdesignofclamps,twocontactcon gurations(i.e.lineandpointcontacts)ofbendingfrettingfatiguecanbeful lledasshowninFig.2[8–10].ThetestrigofbendingfrettingfatigueasshowninFig.2ismountedonaT-slotofthepedestalofthefatiguemachine,andthedetailspecimengeometriesandmechanicalpropertiesofvariedmaterialsarerepresentedinFig.3andTable1.Anormalloadimposedonthefrettingpadsismaintainedataconstant

n

Correspondingauthor.Tel.:þ862887600715;fax:þ862887601304.E-mailaddress:zhuminhao@http://www.77cn.com.cn(M.H.Zhu).

0301-679X/$-seefrontmatter&2014ElsevierLtd.Allrightsreserved.

http://www.77cn.com.cn/10.1016/j.triboint.2013.12.018

134J.F.Pengetal./TribologyInternational76(2014)133–141

Fig.1.Threesimplefrettingfatigue

modes.

Fig.2.Twocontactcon gurationsofbendingfrettingfatiguetestrig.(a)Linecontactand(b)point

contact.

Fig.3.Bendingfrettingfatiguespecimengeometry.(a)30CrNiMo8,(b)7075alloy,(c)LZ50steeland(d)316Lsteel.

Table1

Mainmechanicalpropertiesofthematerials.Mechanicalproperties30CrNiMo8

7075AluminumalloyLZ50Steel316L

s0.2(MPa)

969604.0309.0282

sb(MPa)

1095647.4584.3555

E(GPa)21071210191

HV330150200135

level,whichcanbecalculatedbytheHertzcontacttheory,andthenormalloadismeasuredbyaloadcell.Thebendingstressescanbeloadedbythepistonofthehydraulicservomachine.The

frettingdamageoccursinthecontactzonebetweenthesampleandfrettingpad.

Inthispaper,thebendingfrettingfatiguebehaviorsofvariedcontactpairs,suchasLZ50/52100(sample/frettingpad),7075/52100,316L/52100,30CrNiMo8/17CrNiMo6and17CrNiMo6/40CrNi2MoA,weretestedandanalyzedwithcontactcon gura-tionsofcylinder-on- atandcylinder-on-cylinder.Thenormalcontactloadvariedfrom250Nto1000N,andthebendingloadvariedfrom4.75kNto8kN.Thetestfrequencywas20Hzallthetime.Thefrettingdamagezoneandfracturesurfacewereobservedbyanopticalmicroscopy(OM)andascanningelectricmicroscopy(SEM,Quanta2000)withEDX(EDAX-7760/68ME)

electron

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