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1、2460ADHESIVESANDSEALANTSADHESIVESANDSEALANTSBystrictdefinition,anadhesiveisanysubstancethatfastensorbondsmaterialstobejoined(adherends)bymeansofsurfaceattachment.Thebonddurabilitydependsonthestrengthoftheadhesivetothesubstrate(adhesion)andthestrengthwithintheadhesive(cohesion).Besidesbondin
2、gajoint,anadhesivemayserveasasealagainstforeignmatter.Whenanadhesiveperformsbothbondingandsealingfunctions,itisusuallyreferredtoasanadhesivesealant.Joiningmaterialswithadhesivesofferssignificantbenefitscomparedwithmechanicalmethodsofunitingtwomaterials.Amongthesebenefitsarethatanadhesivedis
3、tributesaloadoveranarearatherthancon-centratingitatapoint,resultinginamoreevendistributionofstresses.Theadhesivebondedjointisthereforemoreresistanttoflexuralandvibrationalstressesthan,forexam-ple,abolted,riveted,orweldedjoint.Anotherbenefitisthatanadhesiveformsasealaswellasabond.Thissealpre
4、ventsthecorrosionthatmayoccurwithdissimilarmetals,suchasaluminumandmagnesium,ormechanicallyfastenedjoints,byprovidingadielectricinsulationbetweenthesubstrates.Anadhesivealsojoinsirregularlyshapedsurfacesmoreeasilythandoesamechanicalfastener.Otherbenefitsincludenegligibleweightadditionandvir
5、tuallynochangetopartdimensionsorgeometry.Mostadhesivesareavailableinliquids,gels,pastes,andtapeforms.Thegrowingvarietyofadhesivesavailablecanmaketheselectionoftheproperadhesiveorsealantachalleng-ingexperience.Inadditiontothetechnicalrequirementsoftheadhesive,timeandcostsarealsoimportantcons
6、iderations.Properchoiceofanadhesiveisbasedonknowledgeofthesuitabilityoftheadhesiveorsealantfortheparticularsubstrates.Appropriatesurfaceprep-aration,curingparameters,andmatchingthestrengthanddurabilitycharacteristicsoftheadhesivetoitsintendeduseareessential.Theperformanceofanadhesive-bonded
7、jointdependsonawiderangeofthesefactors,manyofthemquitecomplex.Adhesivesupplierscanusuallyofferessentialexpertiseintheareaofappropriateselection.Adhesivescanbeclassifiedasstructuralornonstructural.Ingeneral,anadhesivecanbeconsideredstructuralwhenitiscapab
