复合材料板弹簧

TheAnalysisofCompositeLeafSpringbyFiniteElementMethod

andExperimentalMeasurements

JiashiWang,ZaikeLiandQibinJiang

AbstractTheautomobileindustryhasshownincreasedinterestinthereplacementofsteelspringwithE-Glass/Epoxycompositeleafspringduetothehigherstrength-to-weightratio,superiorfatiguestrengthandexcellentcorrosionresistance.InthisworkthecompositeleafspringwiththerectangularcrosssectiondesignedforthecommercialvehiclewasanalyzedbyusingthefiniteelementsoftwareABAQUS,andtheexperimentaltestshadbeenconductedtoconfirmthefiniteelementanalysisresults.Inthefiniteelementanalysis,thestressanalysisandthespringratecomputationhavebeenconductedforthecompositeleafspringsubjectedtothefullload15,000N.Themaximumcompressivestressis309.1MPaatthemiddleofthecompositeleafspring,andthesafefactorcanreachto2.6comparingwiththematerialcompressivestrengthofE-Glass/Epoxy800MPa.Thespringratecom-putedfromABAQUSis160N/mm,andthemaximumloadcapacityofthecompositeleafspringisapproximately34,000N.Themeasurementsofthespringrateandthemaximumloadcapacitywereconductedonthecompositeleafspringfabricatedwiththehotmoldingprocessmethod,andtheyare157.5N/mmand34,280Nrespectively.Comparingtheresultsobtainedfromthefiniteelementanalysiswiththeexperimentalmeasurements,itcanbeseenthattheerrorsare

1.56%forthespringrateand0.82%forthemaximumcapacityload,andthemainperformancesoffabricatedcompositeleafspringhavethegoodagreementwiththedesignedrequirements.

KeywordsCompositematerial

rateMaximumloadcapacityÁÁLeafspringÁFiniteelementanalysisÁSpringF2012-E07-004

J.Wang(&)ÁZ.LiÁQ.Jiang

ZhuzhouTimesNewMaterialTechnologyCo.Ltd.,Zhuzhou,China

e-mail:[email protected]

SAE-ChinaandFISITA(eds.),ProceedingsoftheFISITA2012World

AutomotiveCongress,LectureNotesinElectricalEngineering195,

DOI:10.1007/978-3-642-33835-9_74,ÓSpringer-VerlagBerlinHeidelberg2013823

824J.Wangetal.1Introduction

Inordertomeettheneedsofnaturalresourcesandeconomizeenergy,weightreductionhasbeenthemainfocusofautomobilemanufacturerinrecentyears[1].Weightreductioncanbeachievedprimarilybytheintroductionofbettermaterial,designoptimizationandbettermanufacturingprocesses.Thesuspensionleafspringisoneofthepotentialitemsforweightreductioninautomobile.Becauseofthehigherstrength-to-weightratio,superiorfatiguestrengthandexcellentcorro-sionresistance,thefiberreinforceplastics(FRP)hasshownincreasedinterestinthereplacementofsteelspring[2].WhenthespringismadeofFRP,suchasE-Glass/Epoxy,theweightofthespringcanreduce60–70%,whichcanleadstoreductionoftheunsprungweight.Theelementswhoseweightisnottransmittedtothesuspensionspringarecalledtheunsprungelementsoftheautomobile,includewheelassembly,axles,andpartoftheweightofsuspensionspringandshockabsorbers[3].Thereductionoftheunsprungweightcouldhelpinachievingthevehiclewithimprovedridingqualitiesandincreasedthefuelefficiency.Therefore,theusingofcompositeleafspringnotonlyleadstotheweightreduction,butalsoimprovestheridingqualities.

Someworkshavebeenconductedwithemphasisonthedesignandapplicationofcompositeleafspring,andpartofthemarereviewedhere.Breadmoreintro-ducedtheapplicationofcompositestructuresforautomobiles[4,5].Moriscon-centratedonusingcompositesintherearsuspensionsystem[6].YuandKim[2]designedandoptimizedadoubletaperedbeamforautomotivesuspensionleafspring.Corvi[7]investigatedapreliminaryapproachtocompositebeamdesignanduseditforacompositeleafspring.RajendranandVijayarangandevelopedthegeneticalgorithmsforthedesignoptimizationoflightweightvehiclecompositeleafspring[8],andShivaShankarandVijayarangan[1]investigatedthelightweightvehiclecompositeleafspringconcentratedontheendjointanalysisandtesting.However,thereisthelimitationfortheaboveresearchthatthedesignedcompositeleafspringisusedforthelightweightvehiclewithstaticfullloadbelow10,000Nforonespring.Nowadays,withthedevelopmentoftheauto-mobileindustrials,thecompositeleafspringwithmoreload-bearingisneeded.Meanwhile,thestructure,materialandthefabricateprocessareallimportant.Therefore,itisnecessarytoinvestigatethecompositeleafspringfromsimulationandexperimentaltest,aswellasverifytheeffectivenessandsafetyfortheheavierload-bearingcompositeleafspring.

Inthispaperthecompositeleafspringwithrectanglecrosssectionthattheconstantthicknessandwidthis28980mmisdesignedfortheCommercialvehiclewith15,000Nfullloadforonespring.Thefiniteelement(FE)methodisusedfortheanalysisofstressstate,computationofnumericalspringrateandthemaximumloadcapacity.Meantime,forthevalidityofthedesignedspring,theexperimentisconductedonthecompositeleafspringfabricatedbythehotmoldingprocess.Themeasuredspringrateandthemaximumloadcapacityare

TheAnalysisofCompositeLeafSpring

Fig.1The3-Dstructureof

compositeleafspring825

comparedwiththeFEanalysisresults.Thisworkdevelopstheapplicationofthecompositeleafspringfortheautomobileindustrial.

2FEModeloftheCompositeLeafSpring

Accordingtotheworkingandassemblyconditionsandconsideringthefacilityofmassproduction,themonospringwithconstantrectanglecrosssectionisemployedfortheCommercialvehicle.Thegeometrystructureofthespringcanbedescribedasfollow.Theconstantthicknessandwidthis28980mm,thetotallengthis1,300mm,thearcradiusis1,080mm.Besides,thefullloadingis15,000N,andthedesignedspringrateis160N/mm.The3-DstructurecanbeobtainedintheABAQUSsoftwareasshowninFig.1,andthemodelismeshedwithC3D8I[9]asshowninFig.2.Thedimensionoftheelementsisapproxi-mately5mm,andthereare20,000elements.Becausethecompositeleafspringismainlysubjectedtothemomentloading,andthetensileandcompressivebendingstressisalongthelongitudinaldirection.Therefore,theunidirectionalfiberglassisselectedtobelaidupalongthelongitudinaldirectionofthespring,andthematerialpropertiesoftheE-Glass/EpoxyarelistedinTable1.

3FEAnalysisoftheCompositeLeafSpring

Accordingtotheloadingcondition,thefullload15,000Nisappliedatthemiddleofthecompositeleafspring,andthestressalongthelongitudinaldirectioncanbeobtainedinFig.3.Itcanbeseenthatthemaximumstressisatthemiddlelocation,compressivestressfortheoutersurfaceandtensilestressfortheinnersurface.Meanwhile,theabsolutevalueoftheinnersurfacestressislargerthantheoneoftheoutersurface,whichmaybeduetothatthecompositeleafspringisthecurvedbeam[10].AccordingtothematerialpropertiesasgiveninTable1,thecom-pressivestrengthofcompositematerialissmallerthantensilestrength,sotheverifyofthestressstrengthshouldbebasedonthecompressivestrength.

The

826J.Wangetal.Fig.2Finiteelementmeshofthecompositeleafspring

Table1MaterialpropertiesofE-glass/epoxy

Properties

TensilemodulusalongXdirection(Ex),MPa

TensilemodulusalongYdirection(Ey),MPa

TensilemodulusalongZdirection(Ez),MPa

Tensilestrength,MPa

Compressivestrength,MPa

ShearmodulusalongXYdirection(Gxy),MPa

ShearmodulusalongYZdirection(Gyz),MPa

ShearmodulusalongZXdirection(Gzx),MPa

PoissonratioalongXYdirection(NUxy)

PoissonratioalongYZ-direction(NUxy)

PoissonratioalongZX-direction(NUxy)

Value6,53045,0006,5301,1008002,4332,4331,6980.2170.2170.366Fig.3Thestresscontour

alongthelongitudinal

directionofthecomposite

leafspringsubjectedto

15,000N

maximumcompressivestressis309.1MPaatthemiddleofthecompositeleafspringasshowninFig.3.CombiningthecompressivestrengthinTable1andthecompressivestressinFig3,itcanbecalculatedthatthesafetyfactoris2.6.

Springrateisanimportantparameterforthespringassembledinthevehiclesuspension,anditcanbecomputedfromtheFEanalysisasdescribedasfollow.DuringtheFEanalysis,thevariablessuchastheappliedloadandthedisplacementofthecompositeleafspringcanberecorded,andtheload–displacementcurve

can

TheAnalysisofCompositeLeafSpring

Fig.4Theload–

displacementcurveofthe

compositeleafspring

obtainedfromABAQUS827

beplottedinFig4.Itcanbeseenthattheslopeisalmostconstantduringtheanalysisprocess,andtherelationshipoftheloadandthedisplacementcanbefittedasthelinearfunctionbytheoriginsoftware

y¼160xþ59:6ð1Þ

wherexandyrepresentthedisplacementandloadrespectively,and160shouldbethespringrate.Thesecondpart59.6shouldbethedeviationwhichisintroducebytheFEsimulationandthefunctionfitting.Theerrorcanbecalculatedas59.6/15,0009100%=0.40%,anditcanbeneglectintheengineerapplication.Themaximumloadcapacityisanotherimportantparameterforapplicationofthecompositeleafspring.Theoretically,whenthemaximumcompressivestressofthecompositeleafspringisequaltothecompressivestrength,thespringwillbefractured,andtheloadshouldbethemaximumloadcapacity.DuringtheFEanalysis,themaximumloadissetfrom20,000to70,000N,andtheincreasingstepissetas2,000N.Whentheloadisincreasedto34,000N,thestressstateofthecompositeleafspringcanbeobtainedasshowninFig.5.Themaximumcompressivestressis819.0MPa,whichisjustlargerthanthestressstrength800MPa.Therefore,itissuggestedthat34,000isthemaximumloadcapacityofthecompositeleafspring.

4ExperimentalTesting

Thedesignedcompositeleafspringhadbeenfabricatedwiththehotmoldingprocessmethod,andthethree-pointbendingexperimentisconductedtomeasurethespringrate.Thecompositeleafspringisloadedfromzerototheprescribedmaximumload15,000Nandbacktozerowithloadingspeed200N/s.Afterfivecycles,theload–displacementcurvescanbeobtainedasgiveninFig.6,andfivespringrateswerecomputedfromthecurves,listedas160.2,154.9,156.2,

157.0

828

Fig.5Thestresscontour

alongthelongitudinal

directionofthecomposite

leafspringasthemaximum

compressivestresscloseto

thecompressive

strengthJ.Wangetal.

Fig.6Theload–

displacementcurvesofthe

compositeleafspring

obtainedfromthe

experimentaltests

and159.2N/mm.Theaveragedvalueiscomputedandtakenasthefinalspringrate,whichis157.5N/mm.Comparingtheexperimentalresultswiththevalue160N/mmobtainedfromFEanalysisinSect.3,theerroris1.56%,andtheyhavethegoodagreement.

Afterthemeasurementofthespringrate,themaximumloadismodifiedas70,000N,whichisabouttwotimesofthemaximumloadcapacitytheoretically.Theloadingspeedissetas200N/s,andtheloadingprocessisstoppedautomaticallywhenthecompositeleafspringisfractured.Therecordedload–displacementcurveisobtainedasshowninFig.7,andthemaximumloadcapacitycanbeextractedfromthecurve,whichis34,280N.Comparingtheexperimentalresultwiththevalue34,000NcomputedbyABAQUS,theerroris0.82

%.

TheAnalysisofCompositeLeafSpring

Fig.7Themaximumload

capacitytestofthecomposite

leafspring829

5Conclusions

ThedesignedcompositeleafspringforthecommercialvehiclesisanalyzedbytheFEanalysisandexperimentaltest.IntheFEanalysis,thespringrateandthemax-imumloadcapacityarecomputedbyABAQUSsoftware,andtheyare160N/mmand34,000Nrespectively.Intheexperimentaltests,thethree-pointbendingexperimentsofcompositeleafspringfabricatedwiththehotmoldingprocessareconducted,andthetestedspringrateandmaximumloadcapacityare157.5N/mmand34,280N.ComparingtheresultsobtainedfromtheFEanalysiswiththeexperimentaltests,itcanbeseenthattheerroris1.56%forthespringrateand0.82%forthemaximumcapacityload,andthemainperformancesoffabricatedcompositeleafspringmeetthedesignedrequirements.Inthisworkthedelaminationdamagebetweenthelayersinthecompositeleafspringisnotconsidered,whichwillbeinvestigatedinthenextstep.

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