6.2FormationandcharacteristicsofadhesivejointFormationandcharacteristicsofadhesivejoint1CompositionItiscomposedofadhesivelayer,interfaceareaandsurfacelayerofadherent.AdhesionCohesionAdhesion+cohesion=adhesionforceFormationandcharacteristicsofadhesivejoint1Composition

Twotypesofdamage1“Cohesivefailure”Cohesion<adhesionDamageofadhesivelayeroradhesivelayer2“Adhesionfailure”Cohesion>adhesionInterfacelayerfailure

destructionSlimecohesionMixedfailurInterface

（a）被黏物破壞（b）內(nèi)聚破壞（c）界面破壞（d）混合破壞圖3—54膠接接頭破壞形式Adhesionandadhesionmechanism1Adhesionisaphysical,chemicalandmechanicalaction.The

Adhesion

TheoryMechanicalcombinationtheoryAdsorptiontheoryElectrostatictheoryDiffusiontheory1AdsorptiontheoryTwostages1.Thepolymerintheadhesiveisclosetothesurfaceduetothermalmovement.2.Thedistancebetweentheadhesiveandtheadherentissmallenoughtoproduceadsorption.Theoreticalexplanation:Theadsorptionforceistheattractionbetweenpolarmolecules.2ElectrostatictheoryTheoreticalexplanation：Theadhesiveforcecomesfromtheelectrostaticattractionoftheelectricdoublelayer.FlawsElectrostaticinteractiononlyexistsinthebondingsystemofelectricdoublelayer,whichisnotuniversal.3DiffusiontheoryTheoreticalexplanation：Moleculesformastrongadhesivejointbydiffusion.4MechanicalcombinationtheoryTheadhesivepenetratesintothesurfaceoftheobjecttobeadhered,aftercuring，toproduceadentateormosaicconnection.

Relationshipbetweenwettingandbonding1Wetting2WettabilityNecessaryconditionsforimprovingadhesion：Goodcontactofthewholesurfaceoftheadhesive,fullywet.Thesmallerthecontactangle,thebetterthewettabilityandadhesion.Relationshipbetweenwettingandbonding

contactangleCohesionandcuringofadhesive1CuringofadhesiveTheprocessinwhichanadhesivebecomesasolidafterwettingthesurfaceoftheobjecttobeadhered.2NecessityofcuringTheadhesiveitselfproducesenoughcohesion.Loadbearing.Cohesionandcuringofadhesive3Curingmethodofadhesive（1）Condensationorsolventvolatilization（2）HeatingandpressurizingStressformofadhesivejoint1FourstressformsofadhesivejointStressforms（1）Tearing(stretch)evenly（2）Shear（3）Uneventearing(splitting)（4）StrippedStressformofadhesivejoint1FourstressformsofadhesivejointStressmodeShearPullforceUniformpullingforce(tension)Unevenpullingforce（splitoff）Strippingforce1Uniformpullingforce(tension)Theactionlineofexternalforceisverticaltothegluejoint.Features:

stretching2ShearTheexternalforceactinglineisparalleltotheglueseam.Features:

ShearShearisthebeststressformofadhesivejoint,andtheadhesivestrengthisthehighest.3Uneventearing(splitting)Thesplittingforceisformedattheedge,andthestressconcentrationislarge.Features:

UneventearingForexample,theconnectionofwing,wingribandlongtruss.Thebondingstrengthislow.4

strippingExternaltensionisformedattheedge,andthestressisveryconcentrated.Features:Thebondingstrengthisthelowest.

Therelationshipbetweenlapleng