汽车差速器中英文对照外文翻译文献Word文档下载推荐.docx

汽车差速器中英文对照外文翻译文献Word文档下载推荐.docx

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Failureanalysisofanautomobiledifferentialpinionshaft

Abstract

Differentialisusedtodecreasethespeedandtoprovidemomentincreasefortransmittingthemovementcomingfromtheenginetothewheelsbyturningitaccordingtothesuitableangleinvehiclesandtoprovidethatinnerandouterwheelsturndifferently.Piniongearandshaftattheentrancearemanufacturedasasinglepartwhereastheyareindifferentformsaccordingtoautomobiletypes.Mirrorgearwhichwillworkwiththisgearshouldbecomefamiliarbeforetheassembly.Incaseofanybreakdown,theyshouldbechangedasapair.Generally,inthesesystemsthereareweardamagesingears.Thegearinspectedinthisstudyhasdamageasaformofshaftfracture.

Inthisstudy,failureanalysisofthedifferentialpinionshaftiscarriedout.Mechanicalcharacteristicsofthematerialareobtainedfirst.Then,themicrostructureandchemicalcompositionsaredetermined.Somefractographicstudiesare2005ElsevierLtd.Allrightsreserved.

Keywords:

Differential;

Fracture;

Powertransfer;

Pinionshaft

1.Introduction

Thefinal-drivegearsmaybedirectlyorindirectlydrivenfromtheoutputgearingofthegearbox.Directlydrivenfinaldrivesareusedwhentheengineandtransmissionunitsarecombinedtogethertoformanintegralconstruction.Indirectlydrivenfinaldrivesareusedattherearofthevehiclebeingeithersprungandattachedtothebodystructureorunsprungandincorporatedintherear-axlecasing.Thefinal-drivegearsareusedinthetransmissionsystemforthefollowingreasons[1]:

（a）toredirectthedrivefromthegearboxorpropellershaftthrough90°

and,

（b）toprovideapermanentgearreductionbetweentheengineandthedrivingroad-wheels.

Invehicles,differentialisthemainpartwhichtransmitsthemovementcomingfromtheenginetothewheelsOnasmoothroad,themovementcomestobothwheelsevenly.Theinnerwheelshouldturnlessandtheouterwheelshouldturnmoretodotheturningwithoutlateralslippingandbeingflung.Differential,whichisgenerallyplacedinthemiddlepartoftherearbridge,consistsofpiniongear,mirrorgear,differentialbox,twoaxlegearandtwopinionspidergears.

AschematicillustrationofadifferentialisgiveninFig,1.ThetechnicaldrawingofpinionthefracturedpinionshaftisalsogiveninFig,2,Fig.3showsthephotographofthefracturedpinionshaftandthefracturesectionisindicated.

Indifferentials,mirrorandpiniongeararemadetogetusedtoeachotherduringmanufacturingandthesameserialnumberisgiven.Bothofthemarechangedonconditionthatthereareanyproblems.Inthesesystems,thecommondamageisthewearofgears[2-4].Inthisstudy,thepinionshaftofthedifferentialofaminibushasbeeninspected.Theminibusisadieselvehicledrivenattherearaxleandhasapassengercapacityof15people.Maximumenginepoweris90/4000HP/rpm,andmaximumtorqueis205/1600Nm/rpm.Itstransmissionboxhasmanualsystem（5forward,1back）.Thedamagewascausedbystoppingandstartingtheminibusatatrafficlights.Inthisdifferential,entranceshaftwhichcarriesthepiniongearwasbroken.Variousstudieshavebeenmadetodeterminethetypeandpossiblereasonsofthedamage.Theseare:

•studiescarriedouttodeterminethematerialoftheshaft;

•studiescarriedouttodeterminethemicro-structure;

•studiesrelatedtothefracturesurface.

ThereisacloserphotographofthefracturedsurfacesandfractureareainFig.4.Thefracturewascausedbytakingoutcircularmarkgearseeninthemiddleofsurfaces.

2.Experimentalprocedure

Specimensextractedfromtheshaftweresubjectedtovarioustestsincludinghardnesstestsandmetallographicandscanningelectronmicroscopyaswellasthedeterminationofchemicalcomposition.Alltestswerecarriedoutatroomtemperature.

2.1Chemicalandmetallurgicalanalysis

Chemicalanalysisofthefractureddifferentialmaterialwascarriedoutusingaspectrometer.ThechemicalcompositionofthematerialisgiveninTable1.ChemicalcompositionshowsthatthematerialisalowalloycarburizingsteeloftheAISI8620type.

Hardenabilityofthissteelisverylowbecauseoflowcarbonproportion.Therefore,surfaceareabecomeshardandhighlyenduring,andinnerareasbecomestoughbyincreasingcarbonproportiononthesurfaceareawithcementationoperation.Thisisthekindofsteelwhichisgenerallyusedinmechanicalpartssubjecteddotorsionandbending.Highresistanceisobtainedonthesurfaceandhighfatigueendurancevaluecanbeobtainedwithcompressiveresidualstressbymakingthesurfaceharder[5-7].

Inwhichalloyelementsdistributethemselvesincarbonsteelsdependsprimarilyonthecompoundandcarbideformingtendenciesofeachelement.NickeldissolvesintheαferriteofthesteelsinceithaslesstendencytoformcarbidesthanironSiliconcombinestoalimitedextentwiththeoxygenpresentinthesteeltoformnonmetallicinclusionsbutotherwisedissolvesintheferrite.Mostofthemanganeseaddedtocarbonsteelsdissolvesintheferrite.Chromium,whichhasasomewhatstrongercarbide-formingdependsontheiron,partitionsbetweentheferriteandcarbidephases.Thedistributionofchromiumdependsontheamountofcarbonpresentandifotherstrongercarbide-formingelementssuchastitaniumandcolumbiumamountofcarbonpresentandifotherstrongercarbide-formingelementssuchastitaniumandcolumbiumareabsent.Tungstenandmolybdenumcombinewithcarbontoformcarbidesisthereissufficientcarbonpresentandifotherstrongercarbide-formingelementssuchdatitaniumandcolumbiumareabsent.Manganeseandnickellowertheeutectoidtemperature[8].

PreliminarymicrostructuralexaminationofthefaileddifferentialmaterialisshowninFig.5.ItcanbeseenthatthematerialhasamixedstructureinwhichsomeferriteexistprobablyasaresultofslowcoolingandhighSicontent.HighSicontentinthistypeofsteelimprovestheheattreatmentsusceptibilityaswellas

animprovementofyieldstrengthandmaximumstresswithoutanyreductionofductility[9].Ifthemicro-structurecannotbeinvertedtomartensitebyquenching,areductionoffatiguelimitisobserved.

ThereareareaswithcarbonphaseinFig.5（a）.ThereisthetransitionboundaryofcarburizationinFig.5（b）and（c）showsthematrixregionwithoutcarburization.Asfarasitisseenintherephotographs,thepiecewasfirstcarburized,thenthequenchingoperationwasdonethantempered.Thissituationcanbeunderstoodfromblindmartensiteplates.

2.2Hardnesstests

ThehardnessmeasurementsarecarriedoutbyaMetTest-HTtypecomputerintegratedhardnesstester.Theloadis1471N.Themediumhardnessvalueoftheinteriorregionsisobtainedasobtainedas43HRC.Microhard-nessmeasurementshavebeenmadetodeterminethechanceofhardnessvaluesalongcross-sectionbe-causeofthehardeningofsurfaceareaduetocarburization.TheresultsofVickershardnessmeasurementunderaloadof4.903NareillustratedinTable2.

2.3Inspectionofthefracture

ThedirectobservationsofthepiecewithfracturedsurfacesandSEManalysesaregiveninthischapter.Thecrackstartedbecauseofapossibleprobleminthebottomofnotchcausedtheshafttobebrokencompletely.Thecrackstartedontheouterpart,aftersometimeitcontinuedbeyondthecentreandtherewasonlyalittlepartleft.Andthispartwasbrokenstaticallyduringsuddenstartingofthevehicleatthetrafficlights.Asacharacteristicofthefatigue,therearetworegionsinthefracturedsurface.Theseareasmoothsurfacecreatedbycrackpropagationandaroughsurfacecreatedbysuddenfracture.ThesetworegionscanbeseenclearlyfortheentireproblemasinFig.4.Thefatiguecrackpropagationregioncoversmorethan80%ofthecross-section.

Shaftworksundertheeffectofbending,torsionandaxialforceswhichaffectrepeatedlydependingontheusageplace.Thereisasharpfilletatlevelonthefracturedsection.Forthisreason,stressconcentrationfactorsoftheareahavebeendetermined.Kt=2.4value（forbendingandtension）,andKt=1.9value（fortorsion）havebeenacquiredaccordingtocalculations.Thesearequitehighvaluesforareasexposedtocombinedloading.

Theseobservationsandanalysisshowthatthepiecewasbrokenundertheinfluenceoftorsionwithlownominalstresseselectronmicroscopyshowsthatthefracturehastakenplaceinaductilemanner（Fig.6）.Therearesomeshearlipsinthecrackpropagationregionwhichisaglueoftheplasticsheardeformations.Fig.7showsthebeachmarksofthefatiguecrackpropagation.Thedistancebetweenanylinesisnearly133nm.

3.Conclusions

Afaileddifferentialpinionshaftisanalysedinthisstudy.ThepinionshaftisproducedfromAISI8620lowcarboncarburisingsteelwhichhadacarbursing,quenchingandtemperingheattreatmentprocess.Mechanicalproperties,microstructuralproperties,chemicalcompositionsandfractographicanalysesarecarriedouttodeterminethepossiblefracturereasonsofthecomponent.Asaconclusion,thefollowingstatementscanbedrawn:

•Thefracturehastakenplaceataregionhavingahighstressconcentrationbyafatigueprocedureunderacombinedbending,torsionandaxialstresseshavinghighlyreversiblenature.

•Thecrackofthefractureisinitiatedprobablyatamaterialdefectregionatthecriticallocation.

•Thefractureistakenplaceinaductilemanner.

•Possiblelaterfailuresmayeasilybepreventedbyreducingthestressconcentrationatthecriticallocation

Acknowledgement

Theauthorisveryind