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外文资料--Failure analysis of the suspension spring of a light duty truck.pdf

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外文资料--Failure analysis of the suspension spring of a light duty truck.pdf

endprecautionstobetakentopreventasimilarfailureisrecommended.fromthebottomoftherightrearsuspensionsystem.aroundthepinholeFig.3.Bytheanalysisofthefracturesurfaceitisconcludedthatfailureoccurredbysuddenbrittlefracture.Correspondingauthor.Tel.902122931300x2428fax902122450795.Emailaddressgoksenliitu.edu.trA.Go¨ksenli.www.elsevier.com/locate/engfailanalEngineeringFailureAnalysis142007170–17813506307/seefrontmatterC2112005ElsevierLtd.Allrightsreserved.ThefunctionofthemultileadspringMLSistotransmitandpartlyabsorbtheforcescomingfromtheaxestothechassis.TheMLSconsistsofleadspringswhicharejoinedtogetherwithashacklebushandstabilisiedbyashacklepinFig.21.Bythissuspensionsystem,parabolicflatspringsareused.2.AnalysisofsuspensionsystemofthetruckThetruckwaslifted,rearsuspensionandMLSwasinvestigatedintheUniversitylaboratory.NooverloadingandimpacteffectsontheMLSandloadtransmittingpointsweredetected.BrittlefracturehasoccurredC2112005ElsevierLtd.Allrightsreserved.KeywordsSuspensionspringfailureBrittlefractureInclusionsNotcheffectChangingdesignparameters1.IntroductionThevehicleisa2003modelN2classlightdutytruck.Thetruckhasaclosedrearcabintopreventanoverloadingduringwovenmaterialtransportation.Themaximumpermittableloadis10.300kg.Onlythreetimesthetruckwasoverloaded,butonly1–2overthepermittableload.Theaverageloadingofthetruckwas7.204kgFig.1.After3monthsusageofthetruckat17.251km,fractureoccuredattheflatspringsecondFailureanalysisofthesuspensionspringofalightdutytruckI.B.Eryu¨rek,M.Ereke,A.Go¨ksenliDepartmentofMechanicalEngineering,IstanbulTechnicalUniversity,Gu¨mu¨ssuyu,Istanbul,TurkeyReceived20April2005accepted2November2005Availableonline13February2006AbstractInthispaperthefailureoftherearsuspensionspringisanalyzedindetail.Therearaxlesuspensionsystemofthetruckandfracturedflatspringisinvestigated.Fracturesurface,mechanicalandchemicalpropertiesandmicrostructureofthespringmaterialisanalyzed.Forcesactingonthespringisdeterminedandstrengthcalculationsarecarriedout.Later,failurebehaviourandcauseoffractureisrevealedaftercarefullyanalysisofmicrostructureandresultsofcalculations.Atthedoi10.1016/j.engfailanal.2005.11.007I.B.Eryu¨reketal./EngineeringFailureAnalysis142007170–178171Fig.1.Loadingofthetruck.3.PropertiesofmaterialTwoflatsprings,onedamagedandoneundamaged,wereinvestigatedaccordingchemicalandmechanicalpropertiesandmicroscopicanalyzeresults.3.1.ChemicalanalysisThechemicalanalysisofmaterialsfrombothundamagedanddamagedspringswerecarriedoutbyAtomicAbsorptionSpectroscopyandarereportedinTable1.3.2.MechanicalpropertiesTensileandhardnesstestswereperformedtocomparethemechanicalpropertiesoftwoflatspringswhichcanbeseeninTable2.TheendurancelimitSeofthespringcanbeestimatedusingthesimplifiedequation2Fig.2.Rearsuspensionandmultileadspringsystem.Fig.3.Macroscopyoffracturesurface.Forlimit3.3.MicroscopyThenitralspring4.StressTheinalaxleroughnesstionforcesTable1CarbonandsulfurcontentofthespringsCSFracturedspring0.6750.212Undamagedspring0.7250.028Table2Mechanicalpropertiesofflatsprings172I.B.Eryu¨reketal./EngineeringFailureAnalysis142007170–178theAISI6170springmaterial,thespecifiedUTSis1680MPa3,forwhichtheachievableenduranceSe¼05C2UTSðUltimateTensileStrengthÞ¼810MPað1ÞSpringYieldstrengthMPaTensilestrengthMPaRaptureelongationHardnessHRCFractured14651620636Undamaged155017101032Fig.4.Microstructureofflatsprings.is780MPa.Thisvalueisquiteclosetoourcalculatedvalue.microstructureofthespringmaterialsweredevelopedbyetching,afterdiamondpolishing,with2solutionandwereobservedunderthemicroscopeFig.4.ThephaseswhichcanbeseenintherupturedareMnSenclusions.analysisofthefracturedspringspringsareundertheeffectofdifferentforcesFig.5.StaticforceFZ,Stat,whichiscausedbythenomloadofthevehicle,isactingtotheZdirection.DynamicforceFZ,DynoccursbecauseoftheroadwhichiscausedbyFZ,StatandisactingtotheZdirection.BrakingforceFXactingtotheXdireciscausedbythebrakingdecelerationbofthevehicle.AlinearrelationbetweenbrakingforcesandactingtotheZdirectionexistsintheform4Fig.5.Forcesactingontheflatsprings.l¼bgð2ÞFX¼lðFZStatþFZDynÞð3Þwherebisdecelerationbrakingacceleration2m/s2andlcoefficientofadhesivefrictionl0.2.ThetotalstresssesrwhereoftheberofTheByByanalyzietry,4.1.FatiguwhichTableForcesFZ,Stat36,000I.B.Eryu¨reketal./EngineeringFailureAnalysis142007170–1781733andstressesactingonthespringNFZ,DynNFXNrStatMParDynMParBrakeMParTMPa39,60015,12014315761361rer¼mtC1mdC1msKTC1rUTSð11Þnofatiguefailureisexpected.Thisfatiguelimitstresscanbecalculatedusingthesimplifiedequation8,FordetailedfatigueanalysisS–Ncurveofthespringisestimated.First,alifeNeisspecified,suchas106cyclesforsteel,beyondwhichtheS–Ncurveisassumedtobehorizontal.Hence,afatiguelimit,orstressbelowelifeanalysisStaticsafetyfactorSsisSs¼rYieldrMAX¼1465632¼232ð10ÞKTisdeterminedas1.757.rMAX¼rTC1KT¼361C1175¼632MPað9Þnotcheffectoftheholeistakenintoaccounttoo.Byconsideringthegeometryoftheholeandspringgeomconsideringimpactfactoru1.1theforcesandstressesactingonthespringcanbeseeninTable3.ngthemaximumstressrMAXactingonthefracturedsurface,thestressconcentrationeffectKTrT¼rStat1þFZDynþFXFZStatð8ÞtotalstressesrTactingonthespringisC18C19FZStatDuringbrakingasupplementstressisformed.ThisbrakingstressrBrakecanbecalculatedasrBrake¼FXC1rStatFZStatð7ÞrZDyn¼FZdynC1rStatð6Þnessactingintheformofdynamicloadsonthesprings.Itcanbeexpressedasla,lb,bandh0aregeometricalparametersoftheasymmetricparabolicspring.lalb1700mmlengthspring,b80mmwidthofthespringandh040mmthicknessofthespring,nreferstothenumspringsatthemultileadspringsystemn5.DynamicstressrDynoccursbecauseoftheroadroughrT¼rStatþrDynþrBrakeð4ÞThestaticstressrStatwhichoccurs,becauseofmaximumnominalaxleload,canbecalculatedas5,6rStat¼6FZStatC1lalbnbh20ðlaþlbÞð5ÞrTactingonthespringcanbecalculatedasthesumofstaticrStat,dynamicrDynandbrakingstresBrake.

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