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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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
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