Two-steps clinching of aluminum and Carbon Fiber Reinforced Polymer sheets.pdf
铝和碳纤维增强聚合物片材的两步紧固【中文8873字】
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铝和碳纤维增强聚合物片材的两步紧固【中文8873字】,以及,碳纤维,增强,聚合物,紧固,中文
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VIAITALYKOREACFRPMECHANICALBEHAVIOROFTHEJOINTSTHEMORPHOLOGYANDGEOMETRYOFJOINTSWEREANALYZEDTOUNDERSTANDALFAROMEO4C,BMW7SERIESANDCHEVROLETCORVETTEZ06HYBRIDREPAIRINGANDSTRENGTHENINGSTRUCTURALCOMPONENTS3ANDEVENPROTECTINGFROMFIREANDTHERMALLYINSULATINGLIGHTWEIGHTSTRUCTURALMATERIALS4BECAUSEOFTHEGREATDIFFERENCE,JOININGSUCHMATERIALSSTILLREPRESENTSACHALLENGINGISSUEANDITISGENERALLYMADEBYMEANSOFADHESIVEBONDINGANDMECHANICALJOININGPROCESSESCOMPAREDTOADHESIVEBONDS,MECHANICALJOINTSGENERALLYENSUREHIGHERSTATICSEQUENTINSERTIONOFEXTRAJOININGELEMENTSANDREQUIREADDITIONALPRODUCTIONTIME,ENABLESINGTHEINTEGRITYOFTHECOMPOSITEPARTNOFIBERSINTERRUPTIONPRODUCEDANDTHELOADISDISTRIBUTEDMOREUNIFORMLYSINCEABSENCEOFHOLES5INTHISCASE,THESTRESSISALMOSTUNIFORMWIDTHDIRECTIONWHILEITFOLLOWSAU”SHAPEDISTRIBUTIONALONGTHEBONDINGLENGTH6INTHESEJOINTS,THEDEBONDINGGENERALLYINITIATESATORNEARONEOFTHEBONDEXTREMITIES7COUPLINGMECHANICALJOININGANDADHESIVEBONDINGLEADINGTOHYBRIDJOINTSREPRESENTSANINTERESTINGIMPROVEMENT,SINCEITBRINGSTOGETHERTHEADVANTAGESOFBOTHTHESEJOININGTECHNOLOGIESHYBRIDJOININGHASPROVENTOIMPROVEBOTHTHESTATIC8ANDFATICORRESPONDINGAUTHORATMONTELUCODIROIO,67040AQ,ITALYEMAILADDRESSFRANCESCOLAMBIASEUNIVAQITFLAMBIASECOMPOSITESTRUCTURES1642017180188CONTENTSLISTSAVAILABLESTRUMETALCOMPOSITESTRUCTURESAREALSOWIDELYEMPLOYEDINCIVILAPPLICATIONSWITHDIFFERENTSCOPESREINFORCINGBRIDGECONSTRUCTIONS1,INCREASINGFLEXURALRIGIDITYOFALUMINUMBEAMS2,MATERIALRIVETS,BOLTS,ETCTHATINCREASETHECOSTS,ANDSTRUCTUREWEIGHTDESPITEOFMECHANICALJOINTS,ADHESIVEBONDINGHTTP/DXDOIORG/101016/JCOMPSTRUCT20161207202638223/C2112016ELSEVIERLTDALLRIGHTSRESERVEDENSURISTHEINEMPLOYEDINSEVERALFIELDSINCLUDINGTRANSPORTATIONINDUSTRIES,CIVILINFRASTRUCTUREANDCONSTRUCTIONASTHEYENABLEGREATREDUCTIONINPRODUCTWEIGHT,FUELSAVINGS,INERTIAREDUCTIONANDTHUSHIGHERPERFORMANCESAUTOMOTIVEINDUSTRIESAREINVESTINGHIGHEFFORTSTOREPRODUCEONLARGERSCALETHEBENEFITSOFUSINGHYBRIDMETALCOMPOSITECHASSISINRECENTYEARS,SUCHCHASSISAREBEINGEMPLOYEDONANUMBEROFVEHICLESOFMASSPRODUCTION,INCLUDINGRONMENTALLYFRIENDLYDUETOLOWENERGYREQUIREMENTS,LOWNOISEANDFUMESEMISSIONANDDONOTREQUIRECURINGTIMEHOWEVER,MECHANICALJOININGPROCESSESUSUALLYREQUIREPRELIMINARYDRILLINGOFTHESHEETSTHATMAYDAMAGETHECOMPOSITEMATERIAL,CAUSEFIBERINTERRUPTION,ANDPRODUCESTRESSCONCENTRATIONALTHOUGHTHEYREQUIRESHORTERTIMEASCOMPAREDTOADHESIVEBONDING,MECHANICALJOININGPROCESSESINVOLVEMANUALSTEPSSUCHASPREDRILLINGANDSUBKEYWORDSJOININGMETALCLINCHINGCFRPHYBRIDJOINTSCOMPOSITE1INTRODUCTIONHYBRIDMETALCOMPOSITESTRUCTURESHOWTHERESHAPINGSTEPINFLUENCESTHEMAINQUALITYCRITERIAOFTHEJOINTSANDTHEDAMAGEPRODUCEDONTHECFRPSHEETACCORDINGTOTHEEXPERIMENTALRESULTS,SIMPLECLINCHEDCONNECTIONFAILEDBYPULLOUTTHUS,THECRITICALPARAMETERWASTHEUNDERCUTTHERESHAPINGMETHOD,USINGOPTIMIZEDTOOLSENABLEDTOINCREASETHESTRENGTHOFTHEJOINTSBY32SUCHANIMPROVEMENTWASDUETOANINCREASEINTHEUNDERCUTTHATRESULTEDFROMAHIGHERANDIMPROVEDMATERIALFLOWTHEMAINDEFECTSTHATMAYAPPEARINTHESEJOINTSHAVEBEENIDENTIFIEDASWELLASTHEIRCAUSESC2112016ELSEVIERLTDALLRIGHTSRESERVEDAREMOREANDMOREANDDYNAMICLOADCAPACITYINADDITION,THESEJOINTSAREPERFORMEDINSHORTERTIMEBECAUSETHEYDONOTREQUIREEXTENSIVESURFACEPREPARATIONINCLUDINGETCHING,GRINDING,ANDDEGREASING,ISENVIREVISED12DECEMBER2016ACCEPTED27DECEMBER2016AVAILABLEONLINE28DECEMBER2016CLINCHINGWITHSPLITDIESTHERESHAPINGFORCEWASALSOVARIEDSINGLELAPSHEARTESTSOFSIMPLECLINCHEDANDRESHAPEDSPECIMENSWEREPERFORMEDTODETERMINETHEINFLUENCEOFTHEPROCESSCONDITIONSONTHETWOSTEPSCLINCHINGOFALUMINUMANDCARBONSHEETSFRANCESCOLAMBIASEA,B,DAECHEOLKOCADEPTOFINDUSTRIALANDINFORMATIONENGINEERINGANDECONOMICS,UNIVERSITYOFLAQUILA,BUNIVERSITYOFNAPLESFEDERICOII,CIRTIBSRESEARCHCENTRE,PLETECCHIO80,80125NAPLES,CGRADUATESCHOOLOFCONVERGENCESCIENCE,PUSANNATIONALUNIVERSITY,BUSAN46241,SOUTHARTICLEINFOARTICLEHISTORYRECEIVED27OCTOBER2016ABSTRACTTHEPRESENTPAPERINVESTIGATESFIBERREINFORCEDPOLYMERCOMPOSITEJOURNALHOMEPAGEWWWELSEVIFIBERREINFORCEDPOLYMERGGRONCHI18,ZONAINDUSTRIALEDIPILE,67100AQ,ITALYTHEEFFECTIVENESSOFTWOSTEPSCLINCHINGFORJOININGALUMINUMANDCARBONTOTHISEND,DIFFERENTRESHAPINGTOOLSWEREINVOLVEDAFTERJOININGBYATSCIENCEDIRECTCTURESERCOM/LOCATE/COMPSTRUCTTIGATIONHASBEENPERFORMEDTODETERMINETHEINFLUENCEOFARESHAPINGSTEPWHILEJOININGBYCLINCHINGMETALWITHCOMPOSITESHEETS,INTERMSOFMATERIALFLOW,DAMAGEOFTHECOMPOSITE,CHARACTERISTICDIMENSIONSANDSTRENGTHSTRUCTURES1642017180188181GUESTRENGTH9,DUETOLOWERSTRESSCONCENTRATIONDEVELOPINGDURINGSERVICELIFEBECAUSEOFTHELARGEVARIETYOFMECHANICALJOININGPROCESSES,DIFFERENTMECHANICALCONNECTIONSCANBECOUPLEDWITHADHESIVEBONDING,INCLUDINGBOLTED8,RIVETED10,LASERRIVETING,ANDSELFPIERCERIVETS11SINCETHEINCREASINGEMPLOYMENTOFHYBRIDSTRUCTURESFORMASSPRODUCTIONS,FASTERJOININGPROCESSESAREREQUIREDANUMBEROFNEWPROCESSESHAVEBEENDEVELOPEDTOJOINFIBERREINFORCEDTHERMOPLASTICSFRICTIONSPOTJOINING12,FRICTIONLAPWELDING,13,ULTRASONICWELDING14,ANDLASERASSISTEDDIRECTJOINING15THESEPROCESSESPRODUCEMECHANICALANDCHEMICALADHESIONBETWEENTHETHERMOPLASTICMATRIXOFTHECOMPOSITEANDTHEMETALSURFACEINADDITION,ADVANCEDTHERMOFORMINGPROCESSES,WHICHPRODUCEAMECHANICALINTERLOCKBETWEENTHECOMPONENTSBYPLASTICALLYDEFORMINGTHECOMPOSITEAREALSOSUITABLEFORTHISPURPOSETHERMOFORMINGPROCESSESINCLUDEFRICTIONBASEDSTACKING16,INFRAREDSTACKING17,FRICTIONRIVETING18,ANDFLOWDRILLING19NEVERTHELESS,THESEPROCESSESARENOTSUITABLEFORJOININGCOMPOSITESWITHTHERMOSETTINGMATRICES,SINCETHEYWOULDPRODUCETHERMALDEGRADATIONOFTHEPOLYMERANDMECHANICALDAMAGEOFBOTHTHEFIBERANDTHEMATRIX,TEARINGOFTHEFIBERS,ANDDELAMINATIONOFTHECOMPOSITEONTHEOTHERHAND,FASTMECHANICALJOININGPROCESSESSUCHASCLINCHING2026ANDSELFPIERCERIVETING2729ENABLETOOVERCOMESOMEOFTHEABOVEMENTIONEDCONCERNSINDEED,DESPITEOFCOMMONMECHANICALJOININGMETHODS,WHICHINVOLVERIVETSANDBOLTS,BOTHTHESEPROCESSESDONOTREQUIREPRELIMINARYDRILLINGOFAHOLEINTHESHEETSBEINGJOINED30,31INADDITION,CLINCHINGENABLESADDITIONALADVANTAGES,ASITDOESNOTREQUIREEXTERNALJOININGELEMENTS,WHICHINVOLVEHIGHERCOSTSASWELLASINCREASETHESTRUCTUREWEIGHTMECHANICALCLINCHINGCONSISTSINTHEFORMATIONOFANUNDERCUTTHATFASTENSTWOORMORESHEETSTHEUNDERCUTISPRODUCEDBYAPLASTICDEFORMATIONBYUSINGAPUNCHANDADIECLINCHINGHASBEENORIGINALLYDEVELOPEDTOJOINMETALSHEETSINCLUDINGHIGHSTRENGTHSTEELSANDALUMINUMALLOYSTHEN,ITHASBEENEXTENDEDTOJOINADVANCEDMETALSMAGNESIUMANDTITANIUMALLOYS,ASWELLASTHERMOPLASTICPOLYMERS32,WOODMATERIALS33ANDALSOCOMPOSITESSHEETSWITHFIBERREINFORCEDPOLYMERFRPWITHTHERMOPLASTICMATRIXANDSHORTFIBERS34ANDTHERMOSETTINGMATRIX35WITHLONGFIBERSTHEPROPERDESIGNOFTHECLINCHINGTOOLSISAIMEDATINCREASINGTHEMAINJOINTQUALITYPARAMETERSTHEUNDERCUTANDTHENECKTHICKNESS,WITHOUTDAMAGINGTHESHEETS36MECHANICALCLINCHINGOFCOMPOSITESINTRODUCESFURTHERCONCERNSSINCEDELAMINATIONOFTHECOMPOSITESHOULDBEALSOLIMITEDORPOSSIBLYAVOIDEDTHUS,SPECIFICCONFIGURATIONSSUCHASHOLECLINCHINGHASBEENPROPOSED37,WHICHCONSISTSINPRELIMINARYDRILLINGOFTHECOMPOSITEHOWEVER,HOLECLINCHINGINTRODUCESFURTHERCONCERNSSUCHASLONGERPROCESSINGTIMESOWINGTOTHEPREDRILLINGOPERATION,ANDECCENTRICITYBETWEENTHEPUNCHANDTHEHOLE38FURTHERMORE,DURINGHOLECLINCHING,THEPUNCHSIDEDSHEETISSUBJECTEDTOHIGHERTEARINGSTRESSTHATMAYCOMPROMISETHEINTEGRITYOFTHESHEETSFORMATERIALSWITHPOORFORMABILITY39ASABOVEMENTIONED,THEMECHANICALBEHAVIOROFCLINCHEDJOINTSDEPENDSONGEOMETRICALCHARACTERISTICSTHEUNDERCUTANDTHENECKTHICKNESSTHATDEPENDSONTHEMATERIALFLOWTHUS,TOIMPROVETHESTRENGTHOFTHOSEJOINTS,DIFFERENTAPPROACHESAREPOTENTIALLYSUITABLEINCLUDINGTHEOPTIMIZATIONOFTHETOOLSSETS,ASWELLASTHEDEVELOPMENTOFATWOSTEPSCLINCHINGTHATINVOLVESARESHAPINGSTEPAFTERCLINCHINGTHELATTERMETHODHASBEENINITIALLYPROPOSEDTOREDUCETHEPROTRUSIONHEIGHTANDTHUSTOIMPROVETHEAESTHETICALCHARACTERISTICSOFSUCHJOINTS40HOWEVER,FURTHERRESEARCHESHAVEDEMONSTRATEDTHATFLAMBIASE,DCKO/COMPOSITETWOSTEPSCLINCHINGCANALSOIMPROVETHEMECHANICALSTRENGTHOFCLINCHEDJOINTSMADEONALUMINUMSHEETS41THISRESULTSFROMTHEINCREASEINNECKTHICKNESSANDUNDERCUT24SOFAR,ANYINVESTHEPRESENTINVESTIGATIONANALYZESTWOSTEPSCLINCHINGBASEDONRESHAPINGDEFORMATIONTHATFOLLOWSMECHANICALCLINCHING,ASAMETHODTOIMPROVETHEMECHANICALBEHAVIOROFCLINCHEDCONNECTIONSPERFORMEDONHYBRIDMETALCOMPOSITESJOINTSINPARTICULAR,ALUMINUMALLOYSERIESAA6XXXANDCARBONFIBERREINFORCEDPOLYMERCFRPSHEETSWITHLONGFIBERSANDTHERMOSETTINGMATRIXWEREJOINEDBYCLINCHINGDIFFERENTTYPESOFRESHAPINGTOOLSANDVALUESOFJOININGFORCESWERETESTEDINORDERTODETERMINETHEOPTIMALPROCESSWINDOWMECHANICALTESTSBASEDONSINGLELAPSHEARTESTSWEREPERFORMEDTOCHARACTERIZETHEMECHANICALBEHAVIOROFTHEJOINTSANDTOVERIFYTHEEFFECTIVENESSOFTHERESHAPINGMETHODINADDITION,MORPHOLOGICALANALYSISWASCONDUCTEDTOUNDERSTANDHOWTHERESHAPINGSTEPINFLUENCESTHEMECHANICALBEHAVIOR,THEMAINJOINTSDIMENSIONSANDTHEDAMAGEONCFRPSHEET2MATERIALSANDMETHODS21MATERIALSROLLEDSHEETSOF30MMTHICKALUMINUMALLOYAA6024WEREUSEDINTHISSTUDYTHISISAPRECIPITATIONHARDENABLEALUMINUMALLOYWITHSIANDMGASTHEMAINALLOYINGELEMENTSTHECHEMICALCOMPOSITIONOFTHEALUMINUMWASDETERMINEDBYMEANSOFAXRAYFLUORESCENCESPECTROMETERTHEMAINCHEMICALELEMENTSOFTHEALLOYAREREPORTEDINTABLE1THEALUMINUMSHEETWASCOUPLEDWITHACFRPSHEETWITHATHICKNESSOF14MMTHECFRPLAMINATESWEREMANUFACTUREDUSINGPLAINWEAVESKCHEMICAL,UGN200THECARBONFIBERPREPREGSMRCPYROFILTM,TR30SANDATHERMOSETTINGEPOXYRESINBISPHENOLATYPEEPOXYPHENOLNOVOLACTYPEEPOXYWERECUREDFOR2HAT130C176CTHEINITIALTHICKNESSOFPREPREGFORAPLYWAS03MMBEFORETHEPRESSUREWASAPPLIEDTHEFINALRESINCONTENTWASESTIMATEDTOBEABOUT53,ASREPORTEDINTABLE2THEMECHANICALPROPERTIESANDFABRICATIONPROCEDUREOFTHECFRPSHEETAREREPORTEDIN39THEMAINCHARACTERISTICSANDMECHANICALPROPERTIESOFTHECFRPAREREPORTEDINTABLES2AND322CLINCHINGEQUIPMENTCLINCHEDTESTSWERECARRIEDOUTBYMEANSOFAPORTABLECLINCHINGMACHINEMODELPYTHONBYJURADOSRLRIVOTORTOPERUGIA,ITALYINTHISINVESTIGATION,THECLINCHINGCONFIGURATIONUSEDINTHEFIRSTSTEPWASKEPTUNCHANGEDINTHISSTEPMECHANICALCLINCHING,ASPLITDIEWITHTHREESECTORS,DIEANVILDEPTHH11MMANDINITIALDIAMETERD52MMWASUSED,ASSCHEMATICALLYDEPICTEDINFIG1ATHESPLITDIEWASPREFERREDTOFIXEDGROOVEDONEBECAUSEITGENERALLYPRODUCESLARGERUNDERCUTSWITHLOWERFORMINGFORCESANDITENABLESANEASIEREXTRACTIONOFCOMPOSITECRUMBLESFROMTHEDIECAVITY42THETOOLSETOFTHEFIRSTSTEPALSOINCLUDEDAPUNCHWITHTAPERANGLEOF6C176,DIAMETERD4MMANDFILLETRADIUSOF02MMAFTERPERFORMINGTHEFIRSTJOININGSTEP,THECLINCHINGTOOLSWERESUBSTITUTEDANDTHESECONDSTEPWASPERFORMEDINTHESECONDSTEPRESHAPING,THEHEIGHTOFTHEPUNCHWASVARIEDINORDERTOPRODUCEDIFFERENTPUNCHDIECAVITYGEOMETRIESRESHAPINGDEPTH,RDTHISWASDONEBYCHANGINGTHEHEIGHTHROFANADJUSTABLERING,ASDEPICTEDINFIG1BTHESTUDYALSOINVESTIGATEDTHEEFFECTOFTHETABLE1CHEMICALCOMPOSITIONOFALUMINUMALLOYELEMENTMGSIMNALCONCENTRATION0330960879662STRUCTURESTABLE2MANUFACTURINGCONDITIONSOFCFRPTYPEOFWOVENFABRICTHICKNESSOFLAMINATEMMNUMBERPLAINWEAVE3K147TABLE3MECHANICALPROPERTIESOFCFRPANDAA6082T6ALLOY182FLAMBIASE,DCKO/COMPOSITERESHAPINGFORCEINTHESECONDSTEP,WHICHWASVARIEDOVERTWOLEVELSFJ205KNANDFJ288KN,WHILETHEFORMINGFORCEINTHEFIRSTSTEPKEPTUNCHANGEDFJ288KNTHESEVALUESWERESELECTEDACCORDINGTOPRELIMINARYTESTRESULTSANDTHEMAXIMUMAVAILABLEFORCEOFTHECLINCHINGMACHINETHEEXPERIMENTALPLANISSUMMARIZEDINTABLE4INALLTHETESTS,THEALUMINUMWASPLACEDATTHEPUNCHSIDE23MECHANICALCHARACTERIZATIONOFTHEJOINTSTHEMECHANICALBEHAVIOROFTHEJOINTSWASASSESSEDBYMEANSOFSINGLELAPSHEARTESTSTOTHISEND,AUNIVERSALTESTMACHINEMODELMATERIALELASTICMODULUSGPAYIELDSTRENGTH,R02MPAULTIMATETENSILEAA602469282380CFRP17539627FIG1SCHEMATICOFTHEADOPTEDCLINCHINGTOOLSTABLE4EXPERIMENTALPLANCASERESHAPINGDEPTH,RDMMRESHAPINGFORCE,FJKNNONORESHAPEP20RD22205P28RD22288P20RD11205P28RD21288P20RD0505205P28RD0505288OFPLIESFIBERVOLUMEFRACTIONLAYUPANGLEC1765330450STRENGTHMPAFLOWSTRESSMPABEARINGSTRENGTHMPAILSSMPARP459E0088366191164201718018832231BYMTSWASUSEDUSING25KNFULLSCALEUNDERQUASISTATICCONDITIONSCONSTANTCROSSHEADSPEED1MM/MINTHEGEOMETRYANDSPECIMENDIMENSIONSAREREPORTEDINFIG2AFOREACHJOININGCONDITION,FIVEREPLICATESWEREPERFORMEDANDTHEAVERAGEANDSTANDARDDEVIATIONOFTHEULTIMATELAPSHEARFORCEFRMAXIMUMLOADRECORDEDDURINGTHESHEARTESTANDABSORBEDENERGYW,CALCULATEDASTHEAREAUNDERLYINGTHELOADDISPLACEMENTCURVEOFASHEARTEST,WEREDETERMINEDTOEXAMINETHEDEFORMATIONOFTHEJOINTANDCRACKPROPAGATIONTHROUGHOUTTHECFRPSHEETDURINGTHESINGLELAPSHEARTESTS,ADOUBLEHALVESJOINTSPECIMENTYPEIIWASADOPTED,ASSCHEMATIZEDINFIG2BTHISSPECIMENISCONSTITUTEDBYTWOHALVESJOINTSWHICHWERESECTIONEDAFTERJOININGBYCLINCHINGWHENPRODUCINGTHESESPECIMENSGREATCAREWASPAIDINORDERTOPRODUCETHECROSSSECTIONSPARALLELTOTHELOADINGDIRECTION,ANDTHELINELC1C2,WHICHPASSESBYTHEJOINTSCENTERSC1ANDC2,PERPENDICULARTOTHELOADINGDIRECTION,ASSCHEMATIZEDINFIG2BTHREEREPLICATIONSWEREPERFORMEDFORSPECIMENSTYPEIITOENSUREREPLICABILITYOFTHESETESTSTHISSHAPECONSTRAINEDTHEROTATIONOFTHESPECIMENAROUNDTHEJOINTDURINGTHESHEARTESTTHECROSSSECTIONEVOLUTIONDURINGTHESHEARTESTWASTHUSRECORDEDUSINGA16BITDSLCAMERAMODELINAFIRSTSTEPANDBSECONDSTEPSTRUCTURESFLAMBIASE,DCKO/COMPOSITED5200BYNIKONWITHRESOLUTIONOF6000C24000MOUNTEDONASTEREOMICROSCOPEMODELSTEMIDV4BYZEISS24ANALYSISOFJOINTSMORPHOLOGYTOINVESTIGATETHEINFLUENCEOFTHEAFOREMENTIONEDPROCESSPARAMETERSANDPARTICULARLYTHEDIFFERENCEBETWEENCLINCHEDANDRESHAPEDJOINTS,THECROSSSECTIONSFORALLTHESPECIMENSWEREANALYZEDTHEJOINTSWERECUTINTHEMIDDLEBYMEANSOFALOWSPEEDSAWWITHDIAMONDBLADETHECROSSSECTIONSWERETHUSANALYZEDBYMEANSOFOPTICALMETALLOGRAPHICMICROSCOPEMODELDM5000BYLEICAMICROSYSTEMSANDTHEABOVEMENTIONEDSTEREOSCOPEUNDERREFLECTIVELIGHTFOREACHTOOLSET,THEMAINGEOMETRICALPARAMETERS,NAMELYTHEUNDERCUTTS,NECKTHICKNESSTN,ANDBULGEHEIGHTHDEPICTEDINFIG3,WEREMEASURED3RESULTSANDDISCUSSION31GEOMETRYOFTHEJOINTTHECROSSSECTIONSOFTHECLINCHEDJOINTSMADEBYSINGLESTEPCLINCHINGNORESHAPEANDTWOSTEPSCLINCHINGAREREPORTEDINFIG4THECROSSSECTIONSOFTHEJOINTSSHOWACERTAINASYMMETRYDIFFERENTUNDERCUTANDNECKTHICKNESSVALUESOFTHELEFTANDRIGHTHANDSIDESOFTHEJOINTSTHISISDUETOTHEHIGHSTIFFNESSANDANISOTROPYOFTHECFRPSHEETTHATDRIVESTHEALUMINUMMATERIALTOWARDSDIRECTIONSOFLESSRESISTANCEBETWEENFIBERPLIESTOTHISEND,FIVECROSSSECTIONSFOREACHPROCESSINGCONDITIONWEREANALYZEDASCANBEOBSERVEDFROMFIG4,NOCRACKAPPEARONTHEALUMINUMSHEETATTHENECKREGIONREGARDLESSTHEJOININGCONDITIONCOMPARINGTHECROSSSECTIONSOFTWOSTEPS”JOINTSWITHFIG2SCHEMATICOFTHESPECIMENSUSEDFORCHARACTERIZATIONTESTSASINGLELAPSHEARTEST1642017180188183NORESHAPEONES,SOMEDIFFERENCESCANBEAPPRECIATEDINDEED,THECONTACTSURFACEOFALUMINUMCFRPSHOWNINFIG4AISRELATIVELYREGULAR,WHILE,ONTHEOTHERHAND,BYINCREASINGTHERESHAPINGDEPTHRDTHECONTACTSURFACEBECOMESMOREIRREGULARSHOWINGINTERMEDIATESIDEPROTRUSIONSASALSODEPICTEDINFIG5BINADDITION,EXCESSIVERESHAPINGDEPTHSPRODUCEDSMALLERCONTACTSURFACETHISWASPARTICULARLYEVIDENTINFIG4F,GANDHIGHERMAGNIFICATIONREPORTEDINFIG5CANDBULGEHEIGHTEGFORP28RD2JOINTSH16007MMTHISHASPOTENTIALDETRIMENTALEFFECTSOFTHEMECHANICALBEHAVIOROFTHECLINCHEDJOINTSASREPORTEDIN32INADDITION,WHENHISSMALLERTHANTHETHICKNESSOFTHECFRP,THELASTPLIESOFTHECFRPHOLEARENOTINCONTACTWITHTHEALUMINUMBULGEPROMOTINGTHEONSETOFDELAMINATIONANDCONSEQUENTREDUCTIONINLOADCAPACITYTHEMECHANICALBEHAVIOROFCLINCHEDJOINTSISDETERMINEDBYSEVERALFACTORSINCLUDINGTHEGEOMETRYOFTHEJOINTS,THELENGTHOFANDBTWOHALVES”SPECIMENUSEDFORANALYSISOFMATERIALFLOWOFCROSSSECTIONFIG3MAINGEOMETRICALCHARACTERISTICSOFALUMINUM/CFRPCLINCHEDJOINTSFIG4CROSSSECTIONSOFTHEJOINTSPRODUCEDUNDERDIFFERENTPROCESSINGCONDITIONSFIG5EFFECTOFRESHAPINGONTHECONTACTBETWEENTHEALUMINUMBULGEANDCFRPHOLEBYRESHAPINGTHEAREASREFERTOSELECTIONSDEPICTEDINFIG4184FLAMBIASE,DCKO/COMPOSITESTRUCTURES1642017180188CONTACTARC,THEBULGEHEIGHT,NECKTHICKNESSANDUNDERCUTDIMENSIONS20,THEDAMAGETHATMAYDEVELOPDURINGTHEJOINTFORMATION36ANDSTRAINHARDENINGSINCETHEPROCESSISGENERALLYCARRIEDOUTATROOMTEMPERATUREASWELLASTHEDAMAGEOFTHECFRPNEARTHEHOLETOUNDERSTANDTHEINFLUENCEOFTHERESHAPINGTOOLSONTHEMECHANICALBEHAVIOROFTHEJOINTS,THECHARACTERISTICDIMENSIONS,NAMELYTHEUNDERCUTTS,NECKTHICKNESSTNWERECOMPAREDINFIG6COMPARINGTHECRITICALJOINTDIMENSIONS,ITISEVIDENTTHATTHEUNDERCUT,WHICHISMUCHSMALLERTHANTHENECKTHICKNESS,REPRESENTSTHEKEYPARAMETERTHATDETERMINESTHEMECHANICALBEHAVIOROFTHEJOINTSTHERESHAPINGFORCEISMAINLYEXERTEDONTHEALUMINUMSIDEWALLSOFTHEJOINTDEPENDINGONTHERESHAPINGVALUERD,THISMAYRESULTINDIFFERENTMATERIALFLOWSWHENSMALLVALUESOFRDAREADOPTED,THERESHAPINGSTEPPRODUCESANINCREASEINTHEUNDERCUTANDHIGHERCONTACTPRESSUREBETWEENTHEALUMINUMANDCFRPASALSOSHOWNINTHEMACROGRAPHDEPICTEDINFIG5WHENLARGEVALUESOFRDAREUSED,THEBULGEHEIGHTHREDUCESSINCETHEDIEPUSHESTHEALUMINUMBULGETOWARDSTHEJOINTAXISRATHERTHANEXPANDINGTHEUNDERCUT,ASSHOWNINFIG5C32MATERIALFLOWDURINGTHERESHAPINGSTEP,THEALUMINUMSIDEWALLISPARTIALLYINCONTACTWITHTHEPUNCHGUIDEDALUMINUMASSHOWNINFIG7,WHILETHEBOTTOMPARTOFTHEALUMINUMBULGEISLESSCONSTRAINEDFREEALUMINUMWHENLOWVALUESOFRDAREADOPTEDEGRD05MM,THEFREEALUMINUMREGIONISCHARACTERIZEDBYAREDUCEDHEIGHTTHUS,THISREGIONISMAINLYSUBJECTEDTOUPSETTINGTHATPROMOTESANINCREASEINTHEUNDERCUTANDCONTACTPRESSUREBETWEENTHEALUMINUMANDTHESURROUNDINGCFRP,ASSCHEMATIZEDINFIG7AONTHEOTHERHAND,WHENLARGERVALUESOFRDAREUSEDEGRD10MMANDRD20MMADIFFERENTMATERIALFLOWISPRODUCEDINDEED,UNDERSUCHCONDITIONS,THEGREATERHEIGHTOFTHEFREEALUMINUMREGIONINVOLVESALOWERSTIFFNESSTHUS,AHIGHERINSTABILITYISPRODUCEDTHATPROMOTESANINWARDBENDINGOFTHEALUMINUMBULGE,WHICHRESULTSINREDUCTIONOFTHEUNDERCUTTSANDTHEBULGEHEIGHTHTHEMATERIALFLOWPRODUCEDUNDERSUCHCONDITIONSISSCHEMATIZEDINFIG7BWHENTHEHIGHERLEVELSOFRESHAPINGFORCEWEREUSED,THEMATERIALFLOWISACCENTUATEDTHEN,ITRESULTEDINHIGHERINCREASEINTHEUNDERCUTWHENRD05MMANDAHIGHERREDUCTIONINTHEUNDERCUTFORRD10AND20MMFIG6VARIATIONOFTHENECKTHICKNESSANDUNDERCUTBYADOPTINGDIFFERENTRESHAPINGTOOLSANDJOININGFORCESFLAMBIASE,DCKO/COMPOSITESTRUCTURES1642017180188185FIG7SCHEMATICOFMATERIALFLOWUSINGASMALL33MECHANICALBEHAVIOROFTHEJOINTSLOADDISPLACEMENTCURVESOFCLINCHEDJOINTSMADEBYDIFFERENTTOOLSAREREPORTEDINFIG8ALLTHEJOINTSFAILEDBYPULLOUT,WHICHISATYPICALFAILUREMODEOFCLINCHEDCONNECTIONSCHARACTERIZEDBYRELATIVELYSMALLUNDERCUTSTHECURVESREPORTEDINFIG8SHAREACOMMONBEHAVIORESPECIALLYINTHEFIRSTPATH,WHICHSUGGESTSTHATTHESTIFFNESSOFTHEJOINTISNEGLIGIBLYINFLUENCEDBYTHERESHAPINGSTEPONTHEOTHERHAND,THEJOINTSARECHARACTERIZEDBYDIFFERENTVALUESOFSHEARSTRENGTHANDABSORBEDENERGY,WHICHDEMONSTRATESTHATTHERESHAPINGSTEPCANBEPOSITIVELYEMPLOYEDTOIMPROVETHEMECHANICALBEHAVIOROFCLINCHEDJOINTSBECAUSEOFTHEPULLOUTFAILUREMODE,LOADDISPLACEMENTCURVESSHOWSAGRADUALLOADREDUCTIONAFTERREACHINGTHEPEAKLOADSHEARSTRENGTHOFTHEJOINTUPTOTHECOMPLETELOSSOFTHECARRYINGLOADCAPABILITYTHISBEHAVIORISCOMMONLYPREFERABLEASCOMPAREDTOSTEEPERLOADREDUCTIONTRENDSBRITTLEBEHAVIOROFTHEJOINTASITENABLESMOREENERGYVALU
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