资源预览需要最新版本的Flash Player支持。
您尚未安装或版本过低,建议您
1JurnalMekanikalDecember2008,No.26,768576STRESSANALYSISOFHEAVYDUTYTRUCKCHASSISASAPRELIMINARYDATAFORITSFATIGUELIFEPREDICTIONUSINGFEMRoslanAbdRahman,MohdNasirTamin,OjoKurdiFacultyofMechanicalEngineering,UniversitiTeknologiMalaysia,ABSTRACTThispaperpresentsthestressanalysisofheavydutytruckchassis.Thestressanalysisisimportantinfatiguestudyandlifepredictionofcomponentstodeterminethecriticalpointwhichhasthehigheststress.TheanalysiswasdoneforatruckmodelbyutilizingacommercialfiniteelementpackagedABAQUS.Themodelhasalengthof12.35mandwidthof2.45m.ThematerialofchassisisASTMLowAlloySteelA710CClass3with552MPaofyieldstrengthand620MPaoftensilestrength.Theresultshowsthatthecriticalpointofstressoccurredattheopeningofchassiswhichisincontactwiththebolt.Thestressmagnitudeofcriticalpointis386.9MPa.Thiscriticalpointisaninitialtoprobablefailuresincefatiguefailurestartedfromthehigheststresspoint.KeywordStressanalysis,fatiguelifeprediction,truckchassis1.0INTRODUCTIONTheageofmanytruckchassisinMalaysiaareofmorethan20yearsandthereisalwaysaquestionarisingwhetherthechassisisstillsafetouse.Thus,fatiguestudyandlifepredictiononthechassisisnecessaryinordertoverifythesafetyofthischassisduringitsoperation.StressanalysisusingFiniteElementMethodFEMcanbeusedtolocatethecriticalpointwhichhasthehigheststress.Thiscriticalpointisoneofthefactorsthatmaycausethefatiguefailure.Themagnitudeofthestresscanbeusedtopredictthelifespanofthetruckchassis.Theaccuracyofpredictionlifeoftruckchassisisdependingontheresultofitsstressanalysis.Themoreaccurateresultofstressanalysisthemorevalidthepredictedlifeofobject.Inthisstudy,thestressanalysisisaccomplishedbythecommercialfiniteelementpackagedABAQUS.TheautomotiveindustryvehiclesandcomponentsrepresentsastrategicandimportantbusinesssectorinMalaysia.WiththeeventualtradeliberalizationofASEANFreeTradeAreaAFTA,localautomotivemanufacturersandvendorsshallrequirecarsandcomponentsofworldclassstandard.Noiseandvibrationarekeyelementsinsuchstandard.TheautomotiveindustryinMalaysiaismuchrelyingonforeigntechnology.Truckchassis,whichisimportantstructureoflightweightcommercialvehicle,ismostlydesignedandimportedfromforeigncountry.Inordertochangethistrend,itisnecessarytodevelopandbuiltMalaysianownchassisdesign.Studyandresearchontruckchassisisthusrequiredtoachievethisgoal.Thechassisoftrucksisthebackboneofvehiclesandintegratesthemaintruck2componentsystemssuchastheaxles,suspension,powertrain,cabandtrailer.Thetruckchassisisusuallyloadedbystatic,dynamicandalsocyclicloading.Staticloadingcomesfromtheweightofcabin,itscontentandpassengers.Themovementoftruckaffectsadynamicloadingtothechassis.Thevibrationofenginesandtheroughnessofroadgiveacyclicloading.Theexistingtruckchassisdesignisnormallydesignedbasedonstaticanalysis.Theemphasisofdesignisonthestrengthofstructuretosupporttheloadingplaceduponit.However,thetruckchassishasbeenloadedbycomplextypeofloads,includingstatic,dynamicsandfatigueaspects.Itisestimatedthatfatigueisresponsiblefor85to90ofallstructuralfailures.Theknowledgeofdynamicandfatiguebehavioroftruckchassisinsuchenvironmentisthusimportantsothatthemountingpointofthecomponentslikeengine,suspension,transmissionandmorecanbedeterminedandoptimized.Manyresearcherscarriedoutstudyontruckchassis.KaraogluandKuralayinvestigatedstressanalysisofatruckchassiswithrivetedjointsusingFEM.Numericalresultsshowedthatstressesonthesidemembercanbereducedbyincreasingthesidememberthicknesslocally.Ifthethicknesschangeisnotpossible,increasingtheconnectionplatelengthmaybeagoodalternative.FermeretalinvestigatedthefatiguelifeofVolvoS80BiFuelusingMSC/Fatigue.ConleandChudidresearchaboutfatigueanalysisandthelocalstressstrainapproachincomplexvehicularstructures.StructuraloptimizationofautomotivecomponentsappliedtodurabilityproblemshasbeeninvestigatedbyFerreiraetal.FermérandSvenssonstudiedonindustrialexperiencesofFEbasedfatiguelifepredictionsofweldedautomotivestructures.Filhoet.al.haveinvestigatedandoptimizedachassisdesignforanoffroadvehiclewiththeappropriatedynamicandstructuralbehavior,takingintoaccounttheaspectsrelativetotheeconomicalviabilityofaninitialsmallscaleproduction.Thedesignofanoffroadvehiclechassisisoptimizedbyincreasingthetorsionalstiffness,maintenanceofcenterofgravity,totalweightofstructureandsimplergeometryforreductionofproductioncost.TheintegrationofcomputeraideddesignandengineeringsoftwarecodesPro/Engineer,ADAMS,andANSYStosimulatetheeffectofdesignchangestothetruckframehasbeenstudiedbyCosmeetal.Chiewanichakornetalinvestigatedthebehaviorofatrussbridge,whereanFRPdeckreplacedanolddeterioratedconcretedeck,usingexperimentallyvalidatedfiniteelementFEmodels.Numericalresultsshowthatthefatiguelifeofthebridgeafterrehabilitationwouldbedoubledcomparedtoprerehabilitatedreinforcedconcretedecksystem.Basedontheestimatedtrucktrafficthatthebridgecarries,stressrangesoftheFRPdecksystemlieinaninfinitefatigueliferegime,whichimpliesthatnofatiguefailureoftrussesandfloorsystemwouldbeexpectedanytimeduringitsservicelife.YeandMoanhaveinvestigatedthestaticandfatiguebehaviorofaluminiumboxstiffener/webframeconnectionsusingFiniteElementAnalysisFEAtoprovideaconnectionsolutionthatcanreducethefabricationcostsby3changingthecuttingshapesonthewebframeandcorrespondinglytheweldprocessmeanwhilesufficientfatiguestrengthcanbeachieved.FEbasedfatiguewasusedtolocatethecriticalpointofprobablecrackinitiationandtopredictthelifeinadoorhingesystem.Inthisstudy,stressanalysisofheavydutytruckchassisloadedbystaticforcewillbeinvestigatedtodeterminethelocationofcriticalpointofcrackinitiationasapreliminarydataforfatiguelifepredictionofthistruckchassis.2.0FINITEELEMENTANALYSISOFTRUCKCHASSIS2.1BasicConceptofFEMThefiniteelementmethodFEMisacomputationaltechniqueusedtoobtainapproximatesolutionsofboundaryvalueproblemsinengineering.Simplystated,aboundaryvalueproblemisamathematicalprobleminwhichoneormoredependentvariablesmustsatisfyadifferentialequationeverywherewithinaknowndomainofindependentvariablesandsatisfyspecificconditionsontheboundaryofthedomain.AnunsophisticateddescriptionoftheFEmethodisthatitinvolvescuttingastructureintoseveralelementspiecesofstructure,describingthebehaviorofeachelementinasimpleway,thenreconnectingelementsatnodesasifnodeswerepinsordropsofgluethatholdelementstogether.Thisprocessresultsinasetofsimultaneousalgebraicequations.Instressanalysistheseequationareequilibriumequationsofthenodes.Theremaybeseveralhundredorseveralthousandsuchequations,whichmeanthatcomputerimplementationismandatory.2.2AGeneralProcedureforFEATherearecertaincommonstepsinformulatingafiniteelementanalysisofaphysicalproblem,whetherstructural,fluidflow,heattransferandsomeothersproblem.Thesestepsareusuallyembodiedincommercialfiniteelementsoftwarepackages.Therearethreemainsteps,namelypreprocessing,solutionandpostprocessing.Thepreprocessingmodeldefinitionstepiscritical.Aperfectlycomputedfiniteelementsolutionisofabsolutelynovalueifitcorrespondstothewrongproblem.Thisstepincludesdefinethegeometricdomainoftheproblem,theelementtypestobeused,thematerialpropertiesoftheelements,thegeometricpropertiesoftheelementslength,area,andthelike,theelementconnectivitymeshthemodel,thephysicalconstraintsboundaryconditionsandtheloadings.Thenextstepissolution,inthisstepthegoverningalgebraicequationsinmatrixformandcomputestheunknownvaluesoftheprimaryfieldvariablesareassembled.Thecomputedresultsarethenusedbybacksubstitutiontodetermineadditional,derivedvariables,suchasreactionforces,elementstressesandheatflow.Actuallythefeaturesinthisstepsuchasmatrixmanipulation,numericalintegrationandequationsolvingarecarriedoutautomaticallybycommercialsoftware.Thefinalstepispostprocessing,theanalysisandevaluationoftheresultisconductedinthisstep.Examplesofoperationsthatcanbeaccomplishedinclude4sortelementstressesinorderofmagnitude,checkequilibrium,calculatefactorsofsafety,plotdeformedstructuralshape,animatedynamicmodelbehaviorandproducecolorcodedtemperatureplots.Thelargesoftwarehasapreprocessorandpostprocessortoaccompanytheanalysisportionandthebothprocessorcancommunicatewiththeotherlargeprograms.Specificproceduresofpreandpostaredifferentdependentupontheprogram.2.3TruckdefinitionandclassificationGenerally,truckisanyofvariousheavymotorvehiclesdesignedforcarryingorpullingloads.Otherdefinitionofthetruckisanautomotivevehiclesuitableforhauling.Someotherdefinitionarevarieddependingonthetypeoftruck,suchasDumpTruckisatruckwhosecontentscanbeemptiedwithouthandlingthefrontendoftheplatformcanbepneumaticallyraisedsothattheloadisdischargedbygravity.TherearetwoclassificationsmostapplicabletoRecreationalVehicletowtrucks.Thefirstoneistheweightclasses,asdefinedbytheUSgovernment,rangingfromClass1toClass8aslistedinTable1andTable2.ThesecondisclassifiedintoabroadercategoryLightDutyTruckMediumDutyTruckHeavyDutyTruck2.4ModelofTruckChassisThemodelisdepictedinFigure2.Themodelhaslengthof12.35mandwidthof2.45m.ThematerialofchassisisASTMLowAlloySteelA710CClass3with552MPaofyieldstrengthand620MPaoftensilestrength.Theotherpropertiesofchassismaterialaretabulated.2.5LoadingThetruckchassismodelisloadedbystaticforcesfromthetruckbodyandcargo.Forthismodel,themaximumloadedweightoftruckpluscargois36.000kg.Theloadisassumedasauniformpressureobtainedfromthemaximumloadedweightdividedbythetotalcontactareabetweencargoanduppersurfaceofchassis.2.6BoundaryConditionsThereare3boundaryconditionsBCofmodelthefirstBCisappliedinfrontofthechassis,thesecondandthethirdBCareappliedinrearofchassis.Theyareshown.ThetypeofBC1ispinnedthedisplacementisnotallowedinallaxesandtherotationisallowedinallaxesthatrepresentthecontactconditionbetweenchassisandcaboftruckasshown.TheBC2representsthecontactbetweenchassisanduppersideofspringthattransferloadedweightofcargoandchassistoaxle.ThecontactconditionofBC2intheobjectisshown.IntheBC2,thedisplacementonlyoccurredinaxis2andtherotationrespecttoallaxesiszero.InthepositionwheretheBC3applied,thereisacontactbetweeninsidesurfaceofopeningchassisandoutsidesurfaceofbolt.InABAQUS,thiscontactiscalledinteraction.Inthiscase,thetypeoftheinteractionisfrictionlesssurfacetosurfacecontact.IntheBC3,thedisplacementandtherotationiszeroinallaxesonallofboltsbody.Thisconditioniscalledfixedconstrain.Theboltin
个人主页