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首页 Early-age tensile properties of structural epox…

Early-age tensile properties of structural epoxy adhesives subjected to low-temperature curing .pdf

Early-age tensile properties of…

上传者: erker007 2013-01-03 评分 5 0 138 19 628 暂无简介 简介 举报

简介:本文档为《Early-age tensile properties of structural epoxy adhesives subjected to low-temperature curing pdf》,可适用于工程科技领域,主题内容包含leC(EPproprcctunssstrprotedrmethemechanicalpropertiesbeganonlyaftertheonse符等。

leC(EPproprcctunssstrprotedrmethemechanicalpropertiesbeganonlyaftertheonsetofmaterialvitrificationThiswasincontrasttothedevelopmentoftheglasstransitiontemperature,whichincreasedparticularlybeforevitrificationAproposedanalyticalmodelpredictedthedevelopmentofmechanicalpropertieswell,particularlyunderlowisothermalandcyclictemperatureconditionsgeoustinthevebeerconccentpparativelylowtemperatures(–C)mustbepossibleThenshipglassrties,yageinvestigatedbytheauthorsinapreviousworkThisstudyContentslistsavailableatSciVerseScienceDirectelseInternationalJournalofInternationalJournalofAdhesionAdhesives()–betweenphysicalandmechanicalpropertiesisestablishedandanEmailaddress:thomaskellerepflch(TKeller)earlystagemechanicalpropertiesthereforestronglydependonfocusesontheearlyagedevelopmentofthemechanicalproperties–tensilestiffnessandstrength–ofthesameadhesivesubjectedtothesamelowtemperaturecuringprocedures(isothermal,cyclicandoutdoorcuring)Additionally,therelationship$seefrontmatterElsevierLtdAllrightsreserveddoi:jijadhadhnCorrespondingauthorTel:þfax:þInorderforadhesivebondingtobecomewidelyacceptedintheconstructionindustry,bondingduringwintertimeatcomphysicalproperties–curingdegreeandglasstransitiontemperature–ofacommercialstructuralepoxyadhesivehavebeenregardlessoftheactualenvironmentalconditionsandseasonBecauseofthisandthegenerallylargescaleoftheconnections,theadhesivesusedareinmostcasescoldcuringthermosetsHightemperaturecuringorpostcuringundercontrolledconditionsasinindustrialshopfabricationisnormallynotpossiblenoneofthesepreviousworksfocusedontherelatiobetweenphysicalproperties,suchascuringdegreeortransitiontemperature,andtheearlyagemechanicalpropeparticularlyunderlowcuringtemperaturesTheeffectsoflowtemperaturecuringontheearlisthestrengtheningofstructuresbybondingfiberreinforcedpolymercompositelaminatesontoexistingconcreteorsteelcomponentsAspecificfeatureoftheconstructionindustryisthatconnectionshavetobefabricatedonsiteduetotimeconstraints,curingtemperatureandcuringtimeonthemechanicalpropertiesofbothbulkadhesivematerialsandadhesivelybondedjointseg–However,mostoftheseworksfocusonhotcuringadhesivesandcuringtemperaturesarehighcomparedtothosethatoccurduringthewinteronaconstructionsiteFurthermore,applicationsbeinglimitedtocaseswsegmentswerebondedtogetherobondedtosteelgirders,Arestructuralorsemistructuralconnections,,withstructuralhereconcretebridgeprecastallowingpredictionoftheearlyagephysicalandmechanicalpropertiesasafunctionof(particularlylow)curingtemperaturesIntroductionAdhesivebondingisanadvantathatisalsostartingtoarouseinteresUpuntilnow,however,adhesiveshaElsevierLtdAllrightsreservedconnectiontechnologyconstructionindustrynmostlyusedfornonretebridgeslabswereromisingdevelopmentthephysicalstateoftheadhesiveCuringtemperatureandcuringtimegovernprocessesthattakeplaceduringcuringsuchasgelationandvitrificationAsabasisfordecisionsconcerningthedurationofconstructionstagesorperiodspriortoastructurebeingputintoservice,thereisaneedformodelsandtimeNumerousstudiesareavailablethatinvestigatetheeffectsofEarlyagetensilepropertiesofstructuralowtemperaturecuringOmarMoussa,AnastasiosPVassilopoulos,JuliadCompositeConstructionLaboratory(CCLab),EcolePolytechniqueFederaledeLausannearticleinfoArticlehistory:AcceptedJanuaryAvailableonlineFebruaryKeywords:EpoxyepoxidesMechanicalpropertiesofadhesivesCurehardeningGlasstransitionabstractTheearlyagemechanicaliscriticalfortheoutdooConstructionofthesestruExperimentalinvestigatiostructuralepoxyadhesivesignificantlydeceleratetheAtC,curingwasinhibisamerate,althoughthefojournalhomepage:wwwepoxyadhesivessubjectedtoastro,ThomasKellernFL),Station,BaˆtimentBP,CHLausanne,Switzerlandertydevelopmentofstructuraladhesivesduringlowtemperaturecuringonstructionofengineeringstructures,suchasbridgesorbuildingsresisalsocarriedoutduringwintertimeatlowcuringtemperatureshowedthatthedevelopmentofthetensilepropertiesofacommercialonglydependedonthecuringtemperatureLowercuringtemperaturescessandconsequentlytherateofdevelopmentofmechanicalpropertiesordidnotinitiateatallTensilestrengthandstiffnessdevelopedattherwasslightlydelayedcomparedtothelatterSignificantdevelopmentofviercomlocateijadhadhAdhesionAdhesivesempiricalmodel,basedontheautocatalyticcuringbehavioroftheadhesive,isproposedtopredictthemechanicalpropertiesasafunctionofthecuringprocedureExperimentalinvestigationAdhesivematerialTheadhesiveusedwasSikadurfromSikaSchweizAG,athixotropicbicomponentepoxyadhesive,whichistypicallyemployedinstructuralapplicationsandthereforemaybeseenasrepresentativeacomparisontosimilarstructuraladhesivesisgiveninComponentsaremixedataratioof:byweightoftherespectiveconstituents(resinandhardener)Thetensilestrength(accordingtoDIN)andmodulusofelasticity(ISO)areMPaandGPa,respectivelytheglasstransitiontemperatureofthefullycuredmaterialisC(torsionpendulumaccordingtoASTMD)accordingtothemanufactemperatureswerekeptconstantforhandchangesthenInvestigationofphysicalpropertiesAheatfluxdifferentialscanningcalorimeter(DSCTAQ)connectedtoathermalanalyzerwasusedtomeasuretheheatreleasedduringthecuringreactionTheequipmentissuppliedbyaliquidnitrogencoolingsystemprovidinganinertatmosphere,thusallowingtheDSCcelltoattainlowtemperaturerangesSamplesof–mgwerepreconditionedinaclimatechamber(accuracyofC)accordingtocuringprocedures(A)and(B)duringthetimeperiodslistedinTablesandConstanthumidity()wasmaintainedaboveCtoeliminateanypossibleeffectonthecuringprocess(belowChumiditycouldnotbecontrolled)Afterremovalfromtheclimatechamber,thesampleswererapidlyquenchedinliquidnitrogentostopthecuringreactionSubsequently,thecuringdegree,a,(basedonthemeasuredresidualcure)andthecorrespondingglasstransitiontemperature,Tg,ofthepartiallycuredsampleswereobtainedbyrunningadynamicDSCscanThreesampleswereinvestigatedforeachcombinationofTcureandtcureDataacquisitionwasperformedusingtheaccompanyingsoftware(TAanalysis)InvestigationofmechanicalpropertiesTensilespecimenswerefabricatedinanaluminummoldaccordingtoASTMDwiththedimensionsshowninFigaThemoldwasplacedinaclimatechamberwherespecimenswerecuredaccordingtothecuringprocedures(A)and(B)andtimeperiodslistedinTablesandAgain,therelativehumiditywaskeptconstantat(aboveC)Anothersetofspecimenswassubjectedtocuringprocedure(C)accordingtoppþmpþmpþmpþmFigOutdoorcuringprocedureduringwinterandassociatedmechanicalinvestigationsOMoussaetalInternationalJournalofAdhesionAdhesives()–pþmpþmpþmpþmpþmpþmpþmpþmpþmmmmoccurredatarateofapproximatelyCminThiscuringproceduresimulatedoutdoorsituationsthatcanariseduringwintertime(C)ComplexoutdoorcuringinwinteratvaryingtemperaturesfromapproximatelyCtoþCfordaysbetweenand,asshowninFigTableOverviewofisothermalcuringprocedureandassociatedphysical(p)andmechanical(m)investigationstcure(h)Tcure(C)pppmpþmpppþmpppppþmpturerThebaseresincontainsapproximately(byweight)silicaquartzfillersofsizesrangingbetweenandmmTheadhesiveisusedindifferentapplicationsincludingstructuralbondingbetweenFRPcompositeorsteelplatesandconcrete,differentconcreteelementsandbridgesegmentsCuringproceduresThreedifferentcuringprocedureswereappliedasfollows:(A)Isothermalcuringatfivedifferentisothermaltemperatures(Tcure,,,andC)duringdifferentcuringperiods,tcure,thelatteraresummarizedinTableThetemperaturerangecoveredtheminimumcuringtemperaturesaccordingtotheadhesivemanufacturerandthemaximumtemperaturesthatcanoccurduringsummer,egbelowtheasphaltlayerofabridgeThemaximumcuringtimewash(days)sinceonlytheearlyagewasofinterestinthisstudy(B)CuringatcyclictemperaturesbetweenCandCandbetweenCandC(oncestartingatC,andonceatC,seeTable)TheTableOverviewofcycliccuringprocedureandassociatedphysical(p)andmechanical(m)investigationstcure(h)Tcure(C)–––ppþmpþmmpþmpþmmpþmmmmmmMaxMinAverageExperimentFigmmgtoASTMDand(b)experimentalsetupCCCCCCCCModelVitrificationCuringDegree,α()OMoussaetalInternationalJournalofAdhesionAdhesives()–AminutetimeperiodwasfixedbetweentakingthemoldoutofthechamberandremovingthespecimensOnespecimenwasselectedforexaminationunderambienttemperature,whiletherestwereplacedbackinthechamberandtakenonebyonepriortoinvestigationThiswasimportantespeciallyforspecimenscuredatlowtemperaturesinordertoavoidfurthercuringwhilestoredunderlaboratoryconditionsThewholeexperimentalprogram(physicalandmechanicalinvestigation)wasperformedaccordingtoastandardoperationalprocedure(SOP),whichhadbeenpreviouslyestablishedtoensurethequalityandconsistencyoftheresultsQuasistatictensileexperimentswereperformedaccordingtoASTMDusinganMTSLandmarkkNservohydraulicloadunitcalibratedtoofitsloadcapacitySpecimenswereloadedunderdisplacementcontrolataloadingrateofmmminmmmmmmmmFig(a)SpecimendimensionsaccordinTheeffectoftheloadingrateontheresultedstrengthandstiffnessvaluesisnotexaminedinthepresentworkFordeterminationofYoung’smodulus,E,longitudinalstrainsweremeasuredusinganMTScliponextensometer,asshowninFigbTheextensometerhadagagelengthofmmandaminimumaccuracyofofthemeasuredstrainAdataacquisitionsystemwasusedtorecordthetime,machinedisplacement,strainandcorrespondingloadFivespecimenswereinvestigatedforeachcuringcombinationofTcureandtcureSpecimenswithvoidsorotherdefectsinthefailuresectionwerenottakenintoaccountintheanalysisHowever,aminimumofthreespecimenspercuringcombinationwasconsideredineachcaseExperimentalresultsanddiscussionPhysicalpropertiesThedevelopmentofaandTgatdifferentisothermaltemperatures(,,andC)andcyclictemperatures(–Cand–C)areshowninFigsand,respectivelyModelingcurvesdevelopedinwerealsoaddedCuringproceededandTgdevelopedmoreslowlywithdecreasingcuringtemperatureTheprocessesfurtherdeceleratedaftertheonsetofvitrification,whichisindicatedbythevitrificationcurvesinFigsand(definedaspointswhereTgTcure,see)Vitrification,mmmmhowever,startedlaterwhenthecuringtemperaturewasdecreasedTheTgdevelopmentatcyclictemperatures(–Cand–C)approachedthatofthecorrespondingaverageisothermaltemperatures(andC,respectively),asshowninFigTherelationshipbetweenaandTgforbothisothermalandcycliccuringisshowninFigAdependenceonthecuringtemperaturewasobservedwhencuringtemperaturesweredecreased,forbothisothermalcuring(see)andcycliccuringThiswasduetovitrificationofthematerial,whichoccurredatlowervaluesofTgwherenetworkdensitywaslowInsufficientactivationofthecuringreactiongreatlydeceleratedthereactionofsecondaryaminesandstericalhinderedamines,MechanicalpropertiesThedevelopmentoftensilestrength,ft,andstiffness(Young’smodulus,E)vstime,t,(uptoweeks)duringisothermalcuringisTime,t(hr)FigCuringdegreevstimeofpartiallycuredsamplesatdifferentisothermalandcyclictemperaturesCCCCModelVitrificationStrength,ft(MPa)Time,t(hr)OMoussaetalInternationalJournalofAdhesionAdhesives()–CCCCCCModelVitrificationTg(C)Time,t(hr)FigGlasstransitiontemperaturevstimeofpartiallycuredsamplesatdifferentisothermalandcyclictemperaturesshowninFigaandb,respectivelyBothpropertiesrapidlyincreasedathighcuringtemperatures,whileadelayintheprocesswasobservedparticularlyduringtheinitialcuringstageatlowcuringtemperaturesFigaandbalsoshowsthecurveswhenvitrificationstartedandsignificantincreasesinmechanicalpropertiesonlyoccurredafterthatpoint,particularlyatlowercuringtemperaturesSincevitrificationwasdelayedatlowcuringtemperatures(seeprevioussection),thedevelopmentofmechanicalpropertieswasalsodelayedFurthermorestrength,comparedtostiffnessdevelopment,wasdelayedatlowcuringtemperatures–afterhmaximumstiffnesswasreachedatallcuringtemperatureswhilemaximumstrengthhadnotyetbeenreachedatthelowestcuringtemperatureofCAlso,maximumstiffnessvalueswereloweratCcuringtemperaturethanthoseatCThiswasduetotheincreaseinrandomnessofnetworkcrosslinkingathighcuringtemperaturesaspreviouslyfoundbySancaktaretalByprolongingthecuringperiodatCtoh(month),aslightincreaseinmechanicalproperties(aroundinstiffnessandinstrength)wasachievedcomparedtothosereachedafterhFigshowsthatstrengthandstiffnessrelationshipwaslinear,butdependentoncuringtemperatureatlatercuringstagesThelowerthecuringtemperature,themorestrengthdevelopmentCCCCCCCPascaultWilliamsVendittiGillhamTg(C)Curingdegree,α()FigGlasstransitiontemperaturevscuringdegreeofpartiallycuredsamplesatdifferentisothermalandcyclictemperatureswasdelayedcomparedtostiffnessdevelopmentThedelayinstrengthdevelopmentmaybeattributedtoadelayinthedevelopmentofthemolecularbondquality,whichdependsoncuringtemperature(seeSection)ApotentialdependenceofCCCCModelVitrificationStiffness,E(GPa)Time,t(hr)FigMechanicalpropertydevelopmentatdifferentisothermaltemperaturesandearlystagesofcuring:(a)strengthand(b)stiffnessCCCCCCCCOutdoorsFigStrengthvsstiffnessrelationshipstiffnessdevelopmentoncuringtemperaturemayhavebeenmaskedbythehighfillercontentTheresultsalsoshowthatthescatterinthemeasuredpropertiestendedtobehighestwhentheslopeofthecurvesinFigwassteepestandthendecreasedforlongerdurationsThetensilestrengthandstiffnessdevelopmentundercycliccuringareshowninFigaandb,respectivelyThecomparisonof–Cand–Ccyclesshowsthattheformerdeceleratedpropertydevelopmentconsiderably,morethanthehourdelayintroducedattheClevel,andthatthisdifferenceincreased(uptoapproximatelyhafterhofcure)withfurthercuringAnaverageincreaseinmechanicalpropertiesofmorethanwasobtainedafterhwhentheadhesivecuringcyclestartedbyCinsteadofCThereforebeginningwiththeCcyclehadanegativeeffectontheinitialcrosslinkingandcontinuedtohaveanincreasinglynegativeeffectascuringprogressedAfteraroundh,however,thiswasnolongerthecasesincethetwocurvesapproachedeachotherTheresultsalsofittedwellwiththeresultsfromisothermalcuringshowninFigDuringthe–Ccycles,mechanicalpropertiesdevelopedmorerapidlyascomparedtotheothertwocyclesInadditionandsimilartotheTgresults(showninFig),resultsofthe–CcyclesandCisothermaltemperature(averagetemperaturesofandC)agreedwell,particularlyafterhandaboveTheoutdoorcuringresultsareshowninFigaandbPropertydevelopmentstartedonlyafterh,whenthemaximumtemperaturerosefrombelowCtoalmostCDuringthesubsequentdropofmaximumtemperaturetoC,thedevelopmentalmoststoppedandthenrestartedwhenthemaximumtemperatureroseaboveCagainWhenthemaximumtemperaturefellagain(butremainedaroundC),thestrengthdevelopmentstillcontinuedwhilestiffnessdevelopmentceasedAsaconclusionofthecyclicandoutdoorcuringresults,CseemstobethecriticaltemperatureatwhichcuringstopsordoesnotstartAtslightlyhighertemperatures(–C)curingdoesstart,butataverylowrateRelationshipbetweenphysicalandmechanicalpropertiesThedevelopmentofmechanicalpropertiesdirectlydependedonchangesinthephysicalstate,asshowninFig,whichillustratestherelationshipbetweenmechanicalproperties(strengthandstiffness)andphysicalproperties(Tg)forthedifferentcuringproceduresFigalsoshowsthepointsatwhichvitrificationstartedInthefirstcuringphase,Tgdevelopedsignificantlyincontrasttothemechanicalproperties,whichdidnotdevelopatallThemechanicalpropertiesparticularlydevelopedaftervitrificationstarted,asalreadydiscussedinrelationtoFigDuringthisphase,TgdevelopmentdroppedbehindstrengthandstiffnessdevelopmentItseemsthatthedevelopmentoftheOutdoorModel(Eq)Stiffness,E(GPa)Time,t(hr)FigMechanicalpropertydevelopmentduringoutdoorcuringinwinter:(a)strengthand(b)stiffnessOMoussaetalInternationalJournalofAdhesionAdhesives()–CCCCCCModel(Eq)Model(Eq)CCCModel(Eq)Model(Eq)FigMechanicalpropertydevelopmentatcyclictemperaturesandearlystagesofcuring:(a)strengthand(b)stiffness

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