ppt1、接触CONT-L05-Properties

Thefollowingtopicsarecoveredinthislesson.Lessoncontent:ContactPropertiesWorkshop4:DiskForgingAnalysis(IA)Workshop4:DiskForgingAnalysis(KW),Lesson5:ContactProperties,2hours,Bothinteractive(IA)andkeywords(KW)versionsoftheworkshopareprovided.Completeonlyone.,ContactProperties,Pressure-OverclosureModelsFrictionModelsFrictionEnforcement,Pressure-OverclosureModels(1/8),InAbaqus/Standard,thedefaultpressure-overclosuremodelis“hard”contact“Hard”contactisdepictedbelow.,Pressure-OverclosureModels(2/8),Alternativesto“hard”contactThealternativestohardcontactinclude:“SoftenedcontactContactwithoutseparationUser-definedbehavior(notdiscussedhere),Pressure-OverclosureModels(3/8),SoftenedcontactSoftcontactisusefulasanapproximationofsurfaceconditions.Examples:SurfacecoatingsGasketsLayingapipeontothemuddyseabed,wheretheseabedisthesoftenedsurfaceThreetypes(usingdirectenforcementonly)ExponentialTabularLinear,*SURFACEINTERACTION*SURFACEBEHAVIOR,PRESSURE-OVERCLOSURE=.,Pressure-OverclosureModels(4/8),ExponentialformatThecontactpressurebetweensurfacesincreasesexponentiallywhenthepenetration(overclosure),h,islessthan6c:Atpenetrationsgreaterthan6c,thepressure-overclosurerelationshipislinear.Surfacescomeintocontactwhenclearancemeasuredinthenormaldirectionreducestoc.Bothcandpomustbepositive.,*SURFACEINTERACTION*SURFACEBEHAVIOR,PRESSURE-OVERCLOSURE=exponentialc,po,Pressure-OverclosureModels(5/8),TabularformatInputdatapairs(pi,hi)todefineapiecewiselinearrelationshipbetweenpressureandoverclosure.p1=0,sothefirstdatapairis(0,h1).h1mustbenegative,indicatingaclearance.Datamustbeenteredsuchthatpiandhiincreasemonotonically.Foroverclosuregreaterthanthelastvalueofh,Abaquswillusethestiffnessofthelastpiecewiselinearsegment.,*SURFACEINTERACTION*SURFACEBEHAVIOR,PRESSURE-OVERCLOSURE=tabularpi,hi,Pressure-OverclosureModels(6/8),Linearformat*SURFACEINTERACTION,NAME=name*SURFACEBEHAVIOR,PRESSURE-OVERCLOSURE=linearslopeofthep-hcurve,Pressure-OverclosureModels(7/8),SoftenedcontactcompatibilitychecksAlinearizedcontactstiffnessisusedforeachNewtoniteration.Deviationfromthetruepressurevs.overclosurecurveisquantifiedbytheincompatibility“error,”whichisconsideredintheconvergencecheck.ThisisNOTaruntimeerror;itsroleinestablishingthecorrectcontactstateisanalogoustothatplayedbyaforceresidualindeterminingforceequilibrium.Thefigureaboveshowsanexampleusingtheexponentialformat.,Pressure-OverclosureModels(8/8),ContactwithoutseparationUsefulformodelingtruly“sticky”conditions(adhesives).Thisfeaturecausesthesurfacestobebondedforthedurationofananalysisoncecontactisestablished.Onlynormalcontactisaffectedrelativeslidingisstillallowed.Oftenusedwiththeroughfriction.Usage:*SURFACEINTERACTION*SURFACEBEHAVIOR,NOSEPARATION,FrictionModels(1/15),CharacteristicsoffrictionFrictionalshearstressesmaydevelopatacontactinterfaceifthetwocontactingbodieshaveroughsurfaces.Ifthefrictionalshearstressesreachacriticalvalue,thebodieswillslide.Frictionisahighlynonlineareffect.Solutionsaremoredifficulttoobtainwithfrictionalproblemsthantheyarewithfrictionlessproblems.Donotusefrictionunlessitisphysicallyimportanttodoso.Frictionisnonconservativeunsymmetricequationsystem.Abaqus/Standardwillautomaticallyusetheunsymmetricsolverwhenm0.2orwhencontactpressuredependencyisdetected.,FrictionModels(2/15),Onslipreversalapointcaneitherstick(a)orexhibitreverseslip(b).Formultiplecontactpointsstick-slipbehaviorisinterdependent.Thegeometryofthecontactingbodiesoftenmakestheshear(frictional)andnormal(contact)stressesstronglyinterdependent,makingitmoredifficulttoobtainaconvergedsolution.,FrictionModels(3/15),FourfrictionmodelsareavailableinAbaqus:IsotropicCoulombfriction(withshearstresscap)AnisotropicCoulombfriction(withshearstresscap)ExponentialformwheremsdecaystomkexponentiallyUser-defined(notdiscussedhere),FrictionModels(4/15),IsotropicCoulombfrictionCoulombfrictionisthestandardfrictionmodelimplementedinAbaqus.Tworegimes,governedbythevalueofStick:norelativeslidingwhenteqtcrit.Slip:slidingoccurswhenteq=tcrit.,Notethatt1andt2representtheorthogonalcomponentsofshearstressin3D,FrictionModels(5/15),Thecriticalstressisproportionaltonormalcontactpressure:tcrit=mp.mistheuser-definedcoefficientoffrictionandcanbedefinedintermsofslipvelocity,contactpressure,temperature,andfieldvariable.,FrictionModels(6/15),SyntaxforCoulombfrictionmodel:*SURFACEINTERACTION,NAME=name*FRICTION,TAUMAX=tmaxAnoptionalmaximumshearstressisgivenusingTAUMAX:tcr=min(mp,tmax).tmaxisoftentakenastheshearyieldstressoftheunderlyingmaterial.,FrictionModels(7/15),DefiningisotropicCoulombfrictioninAbaqus/CAE,FrictionModels(8/15),AnisotropicfrictionWithanisotropicfrictionthedefinitionofteqchanges:m1andm2arefrictioncoefficientsinthetwosurfacedirections.istheequivalentfrictioncoefficient.Ifacaptmaxisspecified,thecapsontheindividualcomponentsare,FrictionModels(9/15),Usage:*SURFACEINTERACTION*FRICTION,ANISOTROPIC,TAUMAX=tmax,LAGRANGEAnaveragemaximumshearstress(asinthedefinitionofteqabove)canbespecifiedusingTAUMAX.Thedirectionsofanisotropyarealongtheslipdirectionst1andt2,whicharediscussedonthefollowingpages.,FrictionModels(10/15),DefaultslipdirectionsonsurfacesTheslipincrementfollowsfromDg=tDu,wheretistheslipdirection.Bydefault,theslipdirectionsaredefinedasfollows:Fortwo-dimensionalcontactsurfaces,theslipdirectiontisobtainedbya90clockwiserotationofthecontactdirectionn.Forslavesurfacesdefinedonbeamelementsinspace,thefirstslipdirection,t1,isalongthebeamaxisandthesecondslipdirection,t2,istransversetoit.,FrictionModels(11/15),Formostthree-dimensionalsurfaces,theslipdirections,t1,arethesameasthematerialdirectionsandarefoundby:t1=projectionofglobalx-axisontothemastersurfaceandt2=nt1.Ifthex-axisiswithin0.01ofthecontactdirection,theprojectionoftheglobalz-axisisusedinstead.,FrictionModels(12/15),User-definedslipdirectionsonsurfaces(contactpairsonly)Alternativesurfacedirectionsforthepurposeofprescribingananisotropictangential-contact-interactionmodelorviewingcontactoutputmaybedefinedforthree-dimensionalcontactproblems.Ingeometricallynonlinearanalyses,thesurfacedirectionsrotatewiththesurfaceonwhichthedirectionsweredefined.,FrictionModels(13/15),Usethe*ORIENTATIONoptiontodefinealternativesurfacedirections*SURFACE,NAME=SLAVEdatalinestodefinesurface*SURFACE,NAME=MASTERdatalinestodefinesurface*CONTACTPAIR,INTERACTION=GRATESLAVE,MASTER,ORIENTdefinesdirectionsontheslavesurfaceSLAVE,MASTER,ORIENTdefinesdirectionsonthemastersurface*ORIENTATION,NAME=ORIENTdatalinestodefinetheorientation*SURFACEINTERACTION,NAME=GRATEdatalinestodefinetheinteraction,*ThisfeatureisnotyetsupportedinAbaqus/CAE,FrictionModels(14/15),NonlinearfrictioncoefficientsThefrictioncoefficientsforeithertheisotropicortheanisotropicfrictionmodelscanbemadenonlinearfunctionsoftheequivalentslipvelocityofthenode,theaveragesurfacetemperature,ortheaveragefieldvariablevalue,Forthree-dimensionalcontactpairstheequivalentslipvelocityisdefinedasTheaveragesurfacetemperature(orfieldvariable)iscalculatedusingthevalueofthevariablefromeachsurface:Ifmisafunctionoffieldvariables,theDEPENDENCIESparametermustbeusedonthe*FRICTIONoptiontospecifythenumberoffieldvariabledependencies.,FrictionModels(15/15),KineticfrictionmodelThestaticfrictioncoefficient(ms)isoftendifferentfromthekineticfrictioncoefficient(mk),whichopposesestablishedslipping.Itisassumedthatthefrictioncoefficientdecaysexponentiallyfromthestaticvaluetothekineticvalueaccordingtotheformulawheredcisthedecaycoefficient.Twomethodsfordefiningthismodel:Providethestatic,kinetic,anddecaycoefficientsdirectly.Usetestdatatofittheexponentialmodel,*SURFACEINTERACTION*FRICTION,EXPONENTIALDECAY,FrictionEnforcement(1/11),TwoFrictionEnforcementmethodsareimplementedinAbaqus:Penaltymethod(default)LagrangemultipliermethodThemostcommon(anddefault)combinationofmodel/methodisisotropicCoulombfrictionmodelusingthepenaltyenforcementmethod.,FrictionEnforcement(2/11),PenaltymethodIdealbehaviornoslip(relativesliding)during“stick.”Bydefault,Abaqususesanadaptivepenaltymethod.Itapproximatesstickwithstiffelasticbehavior.Smallelasticslip,gcrit,ispermittedbeforeteq=tcrit.,FrictionEnforcement(3/11),DefineG=penaltystiffness(t=Gg).Ideally,G=.Instead,Gisadaptedcontinuouslydependingonnormalpressureandthefrictioncoefficient.,FrictionEnforcement(4/11),Criticalshearstress,tcr,isafunctionofnormalpressure,p,andthefrictioncoefficient.Bydefault,elasticslip,gcr,isasmallfraction,Ff,ofthecharacteristiccontactsurfacefacedimension,Youcancontrolgcr(seebelow).Thechoiceofelasticslip,gcr,involvesatrade-off:Smallergcrhighersolutionaccuracy,slowerconvergence.Largergcrlowersolutionaccuracy,fasterconvergence.Threeoptionsareavailableforcontrolofgcr.,FrictionEnforcement(5/11),Option1:DefaultvalueofgcrchosenbyAbaqusAbaqusscansallcontactslavesurfacesandcalculatesacharacteristiccontactsurfacefacedimension,wherethesliptoleranceFf=0.005.Ff=0.005isconservativeformostcasesandbalancesaccuracyandefficiency.Usage(thisoptionisthedefault):*SURFACEINTERACTION,NAME=name*FRICTIONm,FrictionEnforcement(6/11),Option2:SameasOption1,butwithuserspecificationofFf.Usewithcare:AlargevalueofFfmayyieldaninaccuratesolution.Asmallvaluemaycauseconvergenceproblemsand/oraninefficientsolution.Usage:*SURFACEINTERACTION,NAME=name*FRICTION,SLIPTOLERANCE=Ffm,FrictionEnforcement(7/11),Option3:Userspecifiesabsolutemagnitudeofgcr.UsefulwhenAbaquscannotcalculateareasonablevalueofNode-basedcontact(nodesetshavenofaces).Modelsinwhichcontactsurfacefacedimensionsvarygreatly.Contactsurfacesalongbeamelements,wherecross-sectionaldimensionsmaybemoreimportantthansegmentlengthindeterminingallowableelasticslip.Modelswithveryrefinedmeshes,inwhichthedefaultvalueofgcristoosmall.Usage:*SURFACEINTERACTION*FRICTION,ELASTICSLIP=gcrm,gcrit,FrictionEnforcement(8/11),LagrangemultipliermethodAnoptionalLagrangemultiplierformulationtoenforceexactstickingconditionsisavailableinAbaqus.Onlyavailableforcontactpairs.Thismethodenforceszerorelativeslipduringstick.LagrangefrictionisnotrecommendedfortheAugmentedLagrangeorPenaltycontactenforcementmethods.Theexactsatisfactionofthefrictionconstraintsisinconsistentwiththeapproximatesatisfactionofthecontactconstraints.Itisintendedforproblemswhereaccurateresolutionofstick/slipbehaviorisofutmostimportance.Example:frictionpresentinrollingcontactbetweentwoelasticbodies(frettingproblems).Typicalmetalformingapplicationsdonotrequiresuchcloseattentiontostick/slipdetail.,FrictionEnforcement(9/11),Thisoptionisattractivebecauseoftheexactstickingconstraint,butithastwodisadvantages:AdditionalLagrangemultipliersincreasetheanalysiscost.RigidconstraintstendtosloworsometimespreventconvergenceoftheNewtonmethod.Convergenceproblemsareparticularlylikelywhenstick/slipandcontactconditionsatneighboringpointsareinterdependent.Usage:*SURFACEINTERACTION,NAME=name*FRICTION,LAGRANGEm,FrictionEnforcement(10/11),Roughfriction“Rough”frictionisimplementedusingtheLagrangemultipliermethod.Norelativemotioncanoccurwhilesurfacesareincontact.Physicallycorrespondstom=.Onlyavailableforcontactpairs.RoughfrictionisnotrecommendedfortheAugmentedLagrangeorPenaltycon