ABAQUS粘接單元應(yīng)用課件

CohesiveBehaviorLecture10OverviewIntroductionCohesiveElementTechnologyConstitutiveResponseinCohesiveElementsViscousRegularizationforCohesiveElementsCohesiveElementExamplesSurface-basedCohesiveBehaviorElement-vs.Surface-basedCohesiveBehaviorNote:Appendix2containsanin-depthdiscussionofmodelingtechniquesforcohesiveelementsusingboththeinteractiveandkeywordsinterfaces.IntroductionIntroductionCohesivebehaviorisusefulinmodelingadhesives,bondedinterfaces,andgaskets.ModelsseparationbetweentwoinitiallybondedsurfacesProgressivefailureofadhesivesDelaminationincompositesIdealizecomplexfracturemechanismswithamacroscopic“cohesivelaw,”whichrelatesthetractionacrosstheinterfacetotheseparation.Thecohesivebehaviorcanbe:Element-basedModeledwithcohesiveelementsSurface-basedModeledwithcontactpairsinAbaqus/Standardand

generalcontactinAbaqus/ExplicitRailcrush:CohesivesurfacesFailedadhesiveisred(CSDMG=1)T-peelanalysis:CohesiveelementsareusedformodelingadhesivepatchesIntroductionElement-basedcohesivebehavior—cohesiveelementsCohesiveelementsallowverydetailedmodelingofadhesiveconnections,includingspecificationofdetailedadhesivematerialproperties,directcontroloftheconnectionmesh,modelingofadhesivesoffinitethickness,etc.CohesiveelementsinAbaqusprimarilyaddresstwoclassesofproblems:AdhesivejointsAdhesivelayerwithfinitethicknessTypicallythebulkmaterialpropertiesareknownDelaminationAdhesivelayerof“zero”thicknessTypicallythebulkmaterialpropertiesarenotknownIntroductionTheconstitutivemodelingdependsontheclassofproblem:Basedonmacroscopicproperties(stiffness,strength)foradhesivejointsContinuumdescription:anyAbaqusmaterialmodelcanbeusedModelingtechniqueisrelativelystraightforward:cohesivelayerhasfinitethickness;standardmaterialmodels(includingdamage).Thecontinuumdescriptionisnotdiscussedfurtherinthislecture.Basedonatraction-separationdescriptionfordelaminationLinearelasticitywithdamageModelingtechniqueislessstraightforward:typicalapplicationsusezero-thicknesscohesiveelements;non-standardconstitutivelawThisapplicationistheprimaryfocusofthislectureIntroductionSurface-basedcohesivebehavior—cohesivesurfacesThisisasimplifiedandeasywaytomodelcohesiveconnections,usingthetraction-separationinterfacebehavior.Itofferscapabilitiesthatareverysimilartocohesiveelementsmodeledwiththetraction-separationconstitutiveresponse.However,itdoesnotrequireelementdefinitions.Inaddition,cohesivesurfacescanbondanytimecontactisestablished(“sticky”contact)Itisprimarilyintendedforsituationsinwhichinterfacethicknessisnegligiblysmall.Itmustbedefinedasasurfaceinteractionproperty.Damageforcohesivesurfacesisaninteractionproperty,notamaterialproperty.Thekinematicsofcohesivesurfacesisdifferentfromthatofcohesiveelements.Bydefault,theinitialstiffnessoftheinterfaceiscomputed

automatically.CohesiveElementTechnologyCohesiveElementTechnologyElementtypes*3DelementsCOH3D8COH3D62DelementCOH2D4AxisymmetricelementCOHAX4Theseelementscanbeembedded

inamodelviasharednodesortieconstraints.BottomfaceTopface*Cohesiveporepressureelementsarealsoavailable.CohesiveElementTechnologyElementandsectiondefinition *ELEMENT,TYPE=COH3D8 *COHESIVESECTION,ELSET=...,

RESPONSE={TRACTIONSEPARATION,CONTINUUM,

GASKET},

THICKNESS={SPECIFIED,GEOMETRY},MATERIAL=...

Specifythicknessindataline

(defaultis1.0)CohesiveElementTechnologyDefaultthicknessofcohesiveelementsTraction-separationresponse:UnitthicknessContinuumandgasketresponseGeometricthicknessbasedonnodalcoordinatesCohesiveElementTechnologyOutputvariablesScalardamage(i.e.,degradation)variableSDEGVariablesindicatingwhetherdamageinitiationcriteriametorexceededDiscussedshortlyElementstatusflagSTATUSCohesiveElementTechnologyImportofcohesiveelementsThecombinationofAbaqus/StandardandAbaqus/Explicitexpandstherangeofapplicationsforcohesiveelements.Forexample,youcansimulatethedamageinastructureduetoanimpacteventthenstudytheeffectofthedamageonthestructure'sloadcarryingcapacity.ConstitutiveResponseinCohesiveElementsConstitutiveResponseinCohesiveElementsDelaminationapplicationsTractionseparationlawTypicallycharacterizedbypeakstrength(N)andfractureenergy(GTC)ModedependentLinearelasticitywithdamageAvailableinbothAbaqus/StandardandAbaqus/ExplicitModelingofdamageunderthegeneralframeworkintroducedearlierDamageinitiationTractionorseparation-basedcriterionDamageevolutionRemovalofelementsNormalmodeShearmodeDependenceoffractureenergy

onmodemixTypicaltraction-separationresponseConstitutiveResponseinCohesiveElementsLinearelasticitywithdamageLinearelasticity

DefinesbehaviorbeforetheinitiationofdamageRelatesnominalstresstonominalstrainNominaltractiontoseparationwithdefaultchoiceofunitthicknessUncoupledtractionbehavior:nominalstressdependsonlyoncorrespondingnominalstrainCoupledtractionbehaviorismoregeneral*ELASTIC,TYPE={TRACTION,COUPLEDTRACTION}ConstitutiveResponseinCohesiveElementsTheelasticmodulusforthetractionseparationlawshouldbeinterpretedasapenaltystiffness.Forexample,fortheopeningmode:Kn

=

Nmax

/dninitInAbaqus,nominalstressandstrainquantitiesareusedforthetractionseparationlaw.Ifunitthicknessisspecifiedfortheelement,thenthenominalstraincorrespondstotheseparationvalue.ElasticresponsegovernedbyKn.Ifyouspecifyanon-unitthicknessforthecohesiveelement,youmustscaleyourdatatoobtainthecorrectstiffnessKn.Exampleonnextslide.Displacementatdamageinitiationinnormal(opening)modeConstitutiveResponseinCohesiveElementsExample:PeeltestmodelAEn=KnheffAbaqusevaluatesthis……whichisequivalenttothisGeometricthickness(basedonnodalcoordinates)oftheadhesivehgeom=1e-3Assumeseparationatinitiation

=1e-3and

Nmax=6.9e9.FormodelA:usegeometricthicknessheff

=hgeom=1e-3

=

/heff

=1;

Nmax=En

=6.9e9Kn=6.9e12FormodelB:specifyunitthickness

heff=1

=

/heff

=1e-3;

Nmax=6.9e9En

=Kn=6.9e12BDamageinitiationMixedmodeconditionsMaximumstress

(orstrain)

criterion:Output:MAXSCRTMAXECRTConstitutiveResponseinCohesiveElements*DAMAGEINITIATION,CRITERION={MAXS,MAXE}ConstitutiveResponseinCohesiveElementsForexample,forModeI(openingmode)theMAXSconditionimpliesdamageinitiateswhensn

=

Nmax.*Damageinitiation,criterion=MAXS290.0E6,200.0E6,200.0E6DamageinitiationpointNmaxTmaxSmaxConstitutiveResponseinCohesiveElementsQuadraticstress(orstrain)interactioncriterion:Nodamageinitiationunder

purecompressionOutput:QUADSCRTQUADECRT*DAMAGEINITIATION,

CRITERION={QUADS,QUADE}ConstitutiveResponseinCohesiveElementsSummaryofdamageinitiationcriteriaMaximumnominalstraincriterion*DAMAGEINITIATION,CRITERION=MAXEQuadraticnominalstraincriterion*DAMAGEINITIATION,CRITERION=QUADEQuadraticnominalstresscriterion*DAMAGEINITIATION,CRITERION=QUADSn:nominalstressinthepurenormalmodes:nominalstressinthefirstsheardirectiont:nominalstressinthesecondsheardirectionn:nominalstraininthepurenormalmodes:nominalstraininthefirstsheardirectiont:nominalstraininthesecondsheardirection*DAMAGEINITIATION,CRITERION=MAXSMaximumnominalstresscriterionwheren,s,andtarecomponentsofrelativedisplacementbetweenthetopandbottomofthecohesiveelement;andToistheoriginalthicknessofthecohesiveelement.ConstitutiveResponseinCohesiveElementsDamageevolutionPostdamage-initiationresponsedefinedby:d

isthescalardamagevariable d=0:undamaged d=1:fullydamaged d

monotonicallyincreasesTypicaldamagedresponseConstitutiveResponseinCohesiveElementsDamageevolutionisbasedonenergyordisplacementSpecifyeitherthetotalfractureenergyorthepostdamage-initiationeffectivedisplacementatfailureMaydependonmodemixModemixmaybedefinedintermsofenergyortractionAreaunderthecurveisthefractureenergyDisplacementatfailureinnormal(opening)modeConstitutiveResponseinCohesiveElementsDisplacement-baseddamageevolutionDamageisafunctionofaneffectivedisplacement:Thepostdamage-initiationsofteningresponsecanbeeitherLinearExponentialTabularLinearpost-initiationresponseConstitutiveResponseinCohesiveElementsKeywordsinterfacefordisplacement-baseddamageevolutionForLINEARandEXPONENTIALsoftening:Specifytheeffectivedisplacementatcompletefailuredfailrelativetotheeffectivedisplacementatinitiationdinit.ForTABULARsoftening:Specifythescalardamagevariableddirectlyasafunctionof

d–dinit.Optionallyspecifytheeffectivedisplacementasfunctionofmodemixintabularform.Abaqusassumesthatthedamageevolutionismodeindependentotherwise.*DAMAGEEVOLUTION,TYPE=DISPLACEMENT,

SOFTENING={LINEAR|EXPONENTIAL|TABULAR},

MIXEDMODEBEHAVIOR=TABULARConstitutiveResponseinCohesiveElementsAbaqus/CAEinterfacefordisplacement-baseddamageevolutionConstitutiveResponseinCohesiveElementsEnergy-baseddamageevolutionThefractureenergycanbedefinedasafunctionofmodemixusingeitheratabularformoroneoftwoanalyticalforms:PowerlawBK(Benzeggagh-Kenane)Forisotropicfailure(GIC

=GIIC),theresponseisinsensitivetothevalueof.ConstitutiveResponseinCohesiveElementsKeywordsinterfaceforenergy-baseddamageevolutionSpecifyfractureenergyasfunctionofmodemixintabularform,orSpecifythefractureenergyinpurenormalandsheardeformationmodesandchooseeitherthePOWERLAWortheBKmixedmodebehavior*DAMAGEEVOLUTION,TYPE=ENERGY,

SOFTENING={LINEAR|EXPONENTIAL},

MIXEDMODEBEHAVIOR={TABULAR|POWERLAW|BK},

POWER=valueConstitutiveResponseinCohesiveElementsAbaqus/CAEinterfaceforenergy-baseddamageevolutionConstitutiveResponseinCohesiveElementsExampleTheprecedingdiscussionwasverygeneralinthesensethatthefullrangeofoptionsformodelingtheconstitutiveresponseofcohesiveelementswaspresented.Inthesimplestcase,Abaqusrequiresthatyouinputtheadhesivethicknessheff

and10materialparameters:

*Elastic,type=traction

En,Et,Es *Damageinitiation,criterion=maxs

Nmax,Tmax,Smax *Damageevolution,type=energy,mixedmodebehavior=bk,power=

GIC,GIIC,GIIICWhatdoyoudowhenyouonlyhave1propertyandtheadhesivethicknessisessentiallyzero?Normal(opening)mode:Traction(nominalstress)Separation(areaunderentirecurve)GICCohesivemateriallaw:Traction,DamageEvolutionDiehl,T.,"ModelingSurface-BondedStructureswithABAQUSCohesiveElements:Beam-TypeSolutions,"ABAQUSUsers'Conference,Stockholm,2005.ConstitutiveResponseinCohesiveElementsExample(cont’d)Commoncase:youknowGTCforthesurfacebond.Assumeisotropicbehavior GIC

=GIIC=GIIIC=

GTCForMIXEDMODEBEHAVIOR=

BK,thismakestheresponseindependentofterm,soset

=anyvalidinputvalue(e.g.,1.0)BondthicknessisessentiallyzeroSpecifythecohesivesectionpropertythicknessheff

=

1.0

Nominalstrains=separation;elasticmoduli=stiffnessIsotropyalsoimpliesthefollowing: En

=Et

=Es=

Eeff(=Keffsincewechoseheff

=

1.0) Nmax

=

Tmax

=

Smax=

TultConstitutiveResponseinCohesiveElementsExample(cont’d)Introduceconceptofdamageinitiationratio: dratio=

dinit/dfail,where0<

dratio<

1.UseGCandequationofatriangletorelatebacktoKeff

andTult:Theproblemnowreducestotwopenaltyterms:dfailanddratio.Assumedratio

=

?.Choosedfailasafractionofthetypicalcohesiveelementmeshsize.Forexample,usedfail

=

0.050

typicalcohesiveelementsizeasastartingpoint.ConstitutiveResponseinCohesiveElementsExample(cont’d)Thus,afterchoosingthetwopenaltyterms,asingle(effective)

traction-separationlawappliestoallmodes(normal+shear):*Cohesivesection,thickness=SPECIFIED,...1.0,::*Elastic,type=TRACTIONKeff,Keff,Keff*Damageinitiation,criterion=MAXSTult,Tult,Tult*Damageevolution,type=ENERGY,mixedmodebehavior=BK,power=1GTC,GTC,GTCEffectiveproperties:Traction(nominalstress)Separation(areaunderentirecurve)GTCCohesivemateriallaw:Traction,DamageEvolutionConstitutiveResponseinCohesiveElementsExample(cont’d)Whatiftheresponseisdynamic?Whataboutthedensity?Thedensityofthecohesivelayershouldalsobeconsideredapenaltyquantity.ForAbaqus/Explicit,theeffectivedensityshouldnotadverselyaffectthestabletimeincrement.Diehlsuggeststhefollowingrule:TheAbaqusAnalysisUser’sManualprovidesadditionalguidelinesfordeterminingacohesiveelementdensitythatminimizestheeffectonthestabletimeincrementinAbaqus/Explicit.

Dtstable=stabletimeincrementwithoutcohesiveelementsinthemodelft2D=0.32213(forcohesiveelementswhoseoriginalnodalcoordinatesrelatetozeroelementthickness)ConstitutiveResponseinCohesiveElementsExample:Double-cantileverbeam(DCB)AlfanoandCrisfield(2001)PureModeIDisplacementcontrolAnalyzedusing2D(CPE4I)elementsDelaminationassumedtooccuralongastraightlineBeams:OrthotropicmaterialCohesivelayer:Traction-separationwithdamageThecohesivepropertiesaregivennextslide.Initialcracku-uCohesivelayer

(set:coh_elems)ConstitutiveResponseinCohesiveElementsProperties:adhesiveInteractiveinterfaceConstitutiveResponseinCohesiveElementsKeywordsinterfaceNote:MoredetailsonmodelingofthisproblemusingcohesiveelementsarediscussedinAppendix2“CohesiveElementModelingTechniques;”therelevantresultswillbediscussedlaterinsection“Surface-basedCohesiveBehavior.”*COHESIVESECTION,ELSET=coh_elems,MATERIAL=cohesive,RESPONSE=TRACTIONSEPARATION,THICKNESS=SPECIFIED

1.0,0.02*MATERIAL,NAME=cohesive*ELASTIC,TYPE=TRACTION5.7e14,5.7e14,5.7e14*DAMAGEINITIATION,CRITERION=QUADS5.7e7,5.7e7,5.7e7*DAMAGEEVOLUTION,TYPE=ENERGY,MIXEDMODEBEHAVIOR=BK,POWER=2.284280,280,280ViscousRegularizationforCohesiveElementsViscousRegularizationforCohesiveElementsCohesiveelementshavethepotentialtocausenumericaldifficultiesinthefollowingcasesStiffcohesivebehaviormayleadtoreducedmaximumstabletimeincrementinAbaqus/ExplicitPotentiallyaddressedthroughselectivemassscalingUnstablecrackpropagationmayleadtoconvergencedifficultiesinAbaqus/StandardPotentiallyaddressedthroughbuilt-inviscousregularizationoptionspecifictocohesiveelementsViscousRegularizationforCohesiveElementsUserinterfaceforviscousregularization *COHESIVESECTION,CONTROLS=control1 *SECTIONCONTROLS,NAME=control1,

VISCOSITY=factorAdd-on

transverseshearstiffnessmay

provideadditionalstability*COHESIVESECTION*TRANSVERSESHEARSTIFFNESSOutputEnergyassociatedwithviscousregularization:ALLCDMoredetailsonviscousregularizationarediscussedinAppendix2CohesiveElementExamplesCohesiveElementExamplesCompositecomponentsinaerospacestructures(Courtesy:NASA)StressconcentrationsaroundstiffenerterminationsandflangesResidualthermalstrainsattheinterfaceatroomtemperatureAnalysisoftheeffectsofresidualstrainsonskin/stiffenerdebondingDelaminationinitiationandpropagationBeginningofseparationAfterseparationAbaqus/Standardsimulationofskin/stiffenerdebondingExampleProblem1.4.5CohesivelayersCohesiveElementExamplesDelaminationofacompositeThismodelisarepresentativeofcompositedelamination.Itcomprises3layersofcompositewithadhesivelayersappliedbetweencompositelayers.Thecompositedelaminatesundertheimpactofaheavymassdisplayedinlightgreenishshadeintheanimation.CohesiveElementExamplesLapjointanalysisLapjointsarecreatedbylayingonematerialontopofanotherandbondingthemtogetherForexample:bondingmaterialsusinganadhesiveorfastenersConnectiontypeinfluencescharacteristicofjointAdhesiveconnection(coveredhere)ComplianceandthicknessofadhesiveFastenerconnectionStiffnessoffastenerMaterialAMaterialBSingle-LapJointCohesiveElementExamplesMeshofthelapjointmodeledusingbothsolidandshellelements2536C3D8IandS4RelementsTransitionfromsolidtoshellelementsisaccomplishedusingthesurface-basedshell-to-solidcouplingconstraint.2116COH3D8elementsLinearelasticmaterialisusedforthecohesivelayer100psimodulusofelasticity(comparedto10.E6foraluminum)0.4Poisson'sratioNotethatthecohesiveelementlayerisinitiallyofzerothickness,andthemeshdensityisfinerthantheconnectedregionsCohesiveElementExamplesTheevolutionofdeformationofthelapjointwithacompliantadhesivelayerSurface-basedCohesiveBehaviorSurface-basedCohesiveBehaviorSurface-basedcohesivebehaviorprovidesasimplifiedwaytomodelcohesiveconnectionswithnegligiblysmallinterfacethicknessesusingthetraction-separationconstitutivemodel.Itcanalsomodel“sticky”contact(surfacescanbondaftercomingintocontact).ThecohesivesurfacebehaviorcanbedefinedforgeneralcontactinAbaqus/ExplicitandcontactpairsinAbaqus/Standard(withtheexceptionofthefinite-sliding,surface-to-surfaceformulation).Cohesivesurfacebehaviorisdefinedasasurfaceinteractionproperty.TopreventoverconstraintsinAbaqus/Explicit,apuremaster-slaveformulationisenforcedforsurfaceswithcohesivebehavior.Surface-basedCohesiveBehaviorUserinterface*SURFACEINTERACTION,NAME=cohesive*COHESIVEBEHAVIOR...*CONTACTPAIR,INTERACTION=cohesivesurface1,surface2Abaqus/Standard*SURFACEINTERACTION,NAME=cohesive*COHESIVEBEHAVIOR...*CONTACT*CONTACTPROPERTYASSIGNMENTsurface1,surface2,cohesiveAbaqus/ExplicitAbaqus/CAESurface-basedCohesiveBehaviorTheformulaeandlawsthatgovernsurface-basedcohesivebehaviorareverysimilartothoseusedforcohesiveelementswithtraction-separationbehavior:linearelastictraction-separation,damageinitiationcriteria,anddamageevolutionlaws.However,itisimportanttorecognizethatdamageinsurface-basedcohesivebehaviorisaninteractionproperty,notamaterialproperty.Tractionandseparationareinterpreteddifferentlyforcohesiveelementsandcohesivesurfaces:tractionseparationGCSurface-basedCohesiveBehaviorLinearelastictraction-separationbehaviorRelatesnormalandshearstressestothenormalandshearseparationsacrosstheinterfacebeforetheinitiationofdamage.Bydefault,elasticpropertiesarebasedonunderlyingelementstiffness.Canoptionallyspecifytheproperties.Recallthisspecificationisrequiredforcohesiveelements.Thetraction-separationbehaviorcanbeuncoupled(default)orcoupled.*COHESIVEBEHAVIOR,TYPE={UNCOUPLED,COUPLED}OptionaldatalinetospecifyKnn,Kss,KttSurface-basedCohesiveBehaviorControllingthecoherednodesTheslavenodestowhichcohesivebehaviorisappliedcanbecontrolledtodefineawiderrangeofcohesiveinteractions:Caninclude:AllslavenodesOnlyslavenodesinitiallyincontactInitiallybondednodesetApplyingcohesivebehaviortoallslavenodes(default)Cohesiveconstraintforcespotentiallyactonallnodesoftheslavesurface.Slavenodesthatarenotinitiallycontactingthemastersurfacecanalsoexperiencecohesiveforcesiftheycontactthemastersurfaceduringtheanalysis.*COHESIVEBEHAVIOR,

ELIGIBILITY=CURRENTCONTACTS1Surface-basedCohesiveBehaviorApplyingcohesivebehavioronlytoslavenodesinitiallyincontactRestrictcohesivebehaviortoonlythoseslavenodesthatareincontactwiththemastersurfaceatthestartofastep.Anynewcontactthatoccursduringthestepwillnotexperiencecohesiveconstraintforces.Onlycompressivecontactismodeledfornewcontact.

*COHESIVEBEHAVIOR,

ELIGIBILITY=ORIGINALCONTACTS2Surface-basedCohesiveBehavior Applyingcohesivebehavioronlytoaninitiallybondednodeset(Abaqus/Standardonly)Restrictcohesivebehaviortoasubsetofslavenodesdefinedusing*INITIALCONDITIONS,TYPE=CONTACT.Allslavenodesoutsideofthissetwillexperienceonlycompressivecontactforcesduringtheanalysis.Thismethodisparticularlyusefulformodelingcrackpropagationalonganexistingfaultline.3*COHESIVEBEHAVIOR,

ELIGIBILITY=SPECIFIEDCONTACTSSurface-basedCohesiveBehaviorExample:Doublecantileverbeam(DCB)AnalyzedebondingoftheDCBmodelusingthesurface-basedcohesivebehaviorinAbaqus/Standard.Tomodeldebondingusingsurface-basedcohesivebehavior,youmustdefine:contactpairsandinitiallybondedcracksurfaces;thetraction-separationbehavior;thedamageinitiationcriterion;andthedamageevolution.YoumayalsospecifyviscousregularizationtofacilitatesolutionconvergenceinAbaqus/Standard.Note:Steps3,4,and5,willbe

coveredlaterinthislecture.Initialcracku-uCohesiveinterface12345Surface-basedCohesiveBehaviorDefinecontactpairsandinitiallybondedcracksurfacesTheinitiallybondedportionoftheslavesurface(i.e.,nodesetbond)isidentifiedwiththe*INITIALCONDITIONS,TYPE=CONTACToption.1Note:Frictionlesscontactisassumed.*NSET,NSET=bond,GENERATE1,121,1*SURFACE,NAME=TopSurf_TopBeam_S1,S1*SURFACE,NAME=BotSurf_BotBeam_S1,S1*CONTACTPAIR,INTER=cohesiveTopSurf,BotSurf*INITIALCONDITIONS,TYPE=CONTACTTopSurf,BotSurf,bondslavesurfacemastersurfacealistofslavenodesthatareinitiallybondedBotSurfTopSurfbondSurface-basedCohesiveBehaviorDefinetraction-separationbehaviorInthismodel,thecohesivebehaviorisonlyenforcedforthenodesetbond.UsetheELIGIBILITY=SPECIFIEDCONTACTSparametertoenforcethisbehavior.Recallthedefaultelasticpropertiesarebased

onunderlyingelementstiffness.Herewespecifytheproperties....*CONTACTPAIR,INTER=cohesiveTopSurf,BotSurf*INITIALCONDITIONS,TYPE=CONTACTTopSurf,BotSurf,bond*SURFACEINTERACTION,NAME=cohesive*COHESIVEBEHAVIOR,ELIGIBILITY=SPECIFIEDCONTACTS5.7e14,5.7e14,5.7e142KnKsKtt1Kn

(Ks,Kt)Kn,Ks,andKt:normalandtangentialstiffnesscomponentsOptionalBotSurfTopSurfbondSurface-basedCohesiveBehaviorDamagemodelingforcohesivesurfacesDamagedtraction-separationresponseforcohesivesurfacesisdefinedwithinthesamegeneralframeworkasusedforcohesiveelements.Thedifferencebetweenthetwoapproachesisthatforcohesivesurfacesdamageisspecifiedaspartofthecontactinteractionproperties.separationsatfailurepeakvaluesofthecontactstresspeakvaluesofthecontactseparationtSurface-basedCohesiveBehaviorUserinterface*SURFACEINTERACTION,NAME=cohesive*COHESIVEBEHAVIOR*DAMAGEINITIATION*DAMAGEEVOLUTION*CONTACTPAIR,INTERACTION=cohesivesurface1,surface2Abaqus/Standard*SURFACEINTERACTION,NAME=cohesive*COHESIVEBEHAVIOR*DAMAGEINITIATION*DAMAGEEVOLUTION*CONTACT*CONTACTPROPERTYASSIGNMENTsurface1,surface2,cohesiveAbaqus/ExplicitAbaqus/CAESurface-basedCohesiveBehaviorDamageinitiationcriteriaMaximumseparationcriterion*DAMAGEINITIATION,CRITERION=MAXUQuadraticseparationcriterion*DAMAGEINITIATION,CRITERION=QUADUQuadraticstresscriterion*DAMAGEINITIATION,CRITERION=QUADStn:normalcontactstressinthepurenormalmodets:shearcontactstressalongthefirstsheardirectiontt:shearcontactstressalongthesecondsheardirectionn:separationinthepurenormalmodes:separationinthefirstsheardirectiont:separationinthesecondsheardirection*DAMAGEINITIATION,CRITERION=MAXSMaximumstresscriterionNote:Recallthedamageinitiationcriteriaforthecohesiveelements:iftheinitialconstitutivethicknessTo=1,

then=/To=.Inthiscase,theseparationmeasuresforbothapproachesareexactlythesame.Surface-basedCohesiveBehaviorExample:DoublecantileverbeamDefinethedamageinitiationcriterionThequadraticstresscriterionisspecifiedforthisproblem.3...*CONTACTPAIR,INTER=cohesiveTopSurf,BotSurf*INITIALCONDITIONS,TYPE=CONTACTTopSurf,BotSurf,bond*SURFACEINTERACTION,NAME=cohesive*COHESIVEBEHAVIOR,ELIGIBILITY=SPECIFIEDCONTACTS5.7e14,5.7e14,5.7e14*DAMAGEINITIATION,CRITERION=QUADS5.7e7,5.7e7,5.7e7BotSurfTopSurfbondSurface-basedCohesiveBehaviorDamageevolutionForsurface-basedcohesivebehavior,damageevolutiondescribesthedegradationofthecohesivestiffness.Incontrast,forcohesiveelementsdamageevolutiondescribesthedegradationofthematerialstiffness.Damageevolutioncanbebasedonenergyorseparation(sameasforcohesiveelements).Specifyeitherthetotalfractureenergy(apropertyofthecohesiveinteraction)orthepostdamage-initiationeffectiveseparationatfailure.MaydependonmodemixModemixmaybedefined

intermsofenergyortractiontGTCSeparation-baseddamageevolutionDamageisafunctionofaneffectiveseparation:Aswithcohesiveelements,thepostdamage-initiationsofteningresponsecanbeeither:LinearExponentialTabularSurface-basedCohesiveBehaviortLinearpost-initiationresponseSurface-basedCohesiveBehaviorSeparation-baseddamageevolution(cont’d)Usage:*DAMAGEEVOLUTION,TYPE=DISPLACEMENT,

SOFTENING={LINEAR|EXPONENTIAL|TABULAR},

MIXEDMODEBEHAVIOR=TABULARSurface-basedCohesiveBehaviorEnergy-baseddamageevolutionAswithcohesiveelements,theenergy-baseddamageevolutioncriterioncanbedefinedasafunctionof