ppt1、接触CONT-LA01-N2S

Thefollowingtopicsarecoveredinthislesson.Lessoncontent:Node-to-SurfaceFormulation,Appendix1:Node-to-SurfaceFormulation,2hours,Node-to-SurfaceFormulation,DiscretizationFiniteSliding:SurfaceConsiderationsSmallSlidingCharacteristicsSmallSliding:LocalContactPlaneSmallSliding:SurfaceConsiderations,Discretization(1/3),Keyimplicationofthestrictmaster/slaveformulation:Slavenodescannotpenetratemastersurfacesegments.Nodesonthemastersurfacecanpenetrateslavesurfacesegments.,Discretization(2/3),AgrosspenetrationofamastersurfaceintoacoarselymeshedslavesurfacecausessolutioninaccuracyRefinementoftheslavesurfaceimprovescontactresolution,Discretization(3/3),MeshdetailsandthechoiceofmasterandslaverolescanbekeytoconvergencebehaviorandsolutionaccuracywiththeN-to-SdiscretizationAssignmentofmasterandslaverolesUsuallyitisbettertohavethemore-refinedsurfaceactastheslavesurfaceOtherfactors:ThestifferbodyshouldbethemasterTheactivecontactregionshouldchangemostrapidlyonthemastersurfaceThisminimizescontactstatuschanges(constraintsareprimarilyassociatedwithslavenodes)Contactnearcornersandperimetersofthemastersurfaceshouldbeminimized,FiniteSliding:SurfaceConsiderations(1/22),Acommonissuefornode-to-surfacecontactisslavenodesnaggingCornersorsmallprotrusionsofajaggedmastersurfacescanpenetratethespacesbetweenslavenodescausingthemtosnag.,FiniteSliding:SurfaceConsiderations(2/22),Abaqus/Standardautomaticallysmoothesthemastersurfaceforcontactcalculationsutilizingthenode-to-surfacediscretizationtominimizesnagging.Mastersurfacesmoothingensuresthatmastersurfaceshavecontinuoussurfacenormalsatallpoints.Thisminimizesthetendencyofslavenodestosnag.Snaggingisnotaproblemforthesurface-to-surfacediscretization.Abaqusaccountsforthespacesbetweennodesonboththemasterandslavesurfaces.Thus,nosmoothingofthemastersurfaceoccurswhenusingthesurface-to-surfacediscretization.,FiniteSliding:SurfaceConsiderations(3/22),MastersurfacesmoothingAbaqus/Standardautomaticallysmoothesthefollowingtypesofmastersurfacesfornode-to-surfacefinitesliding:Two-dimensionaldeformableThree-dimensionaldeformableSurfacesdefinedonrigidelementsAbaqus/Standarddoesnotautomaticallysmoothanalyticalrigidsurfaces.Smoothinghasnoeffectonslavesurfaces.Smoothingisdoneonlywhentwoadjoiningsurfacefacetshavedifferentnormals.,FiniteSliding:SurfaceConsiderations(4/22),Interfaceforcontrollingmastersurfacesmoothing,*contactpair,smooth=0.2bearing,shaft,FiniteSliding:SurfaceConsiderations(5/22),Whensmoothingatwo-dimensionaldeformablemastersurface,Abaqus/Standardconstructsaparabolicarcbetweenfirst-orderelementsandacubicarcbetweensecond-orderelements.Thus,theunderlyinggeometryofthemastersurfaceisaltered.,DEGREEOFSMOOTHING=0.4Maximumsmoothingvalue=0.5.,DEGREEOFSMOOTHING=0.2Defaultsmoothingvalueof0.2.Smoothedcornerisaparabolicsegmentfittedtangenttotheoriginalstraightsegments.,DEGREEOFSMOOTHING=0Nosmoothing(notadvised).,FiniteSliding:SurfaceConsiderations(6/22),Forathree-dimensionalmastersurfacetheSMOOTHparameterdefinesthefractionoftheelementfacetthatretainstheelementfacetsnormal.Pointswithinthedashedboxretaintheelementfacetsnormal.Pointsoutsidetheboxuseasmoothed(averaged)normal.Thefacetedgeometryofthemastersurfaceisnotaltered(onlyitsnormalsare).Thisalgorithmgeneratesunsymmetrictermsinthesystemofequations.,FiniteSliding:SurfaceConsiderations(7/22),MastersurfacesmoothingalongsymmetryplanesFornode-to-surfacecontact,thedefaultnormalvectorsthatAbaqus/Standardcreatesatnodesalongasymmetryplanewilloftenbeinaccurateforcurvedsurfaces.Theinaccuratemastersurfacenormalsarecausedbythefacetedgeometryofthemodel.,FiniteSliding:SurfaceConsiderations(8/22),Ifthedefaultnormalfornode1onthemastersurface,N1,isused,node100willnever“see”themastersurface(becauseofthesymmetryconditionitcannotmoveinthey-direction).Eveniftheoutercylinderwasthemastersurface,therewouldstillbeaproblemwiththedefaultnodalnormalvectoralongthesymmetryplane.Node1will“see”themastersurface.However,thecontactconditionwillapplyaconstraintinthe(vertical)y-directionbecauseN100hasaverticalcomponent.Thisconstraintwillconflictwiththeoneimposedbythesymmetryboundarycondition,causingnumericalproblems(overconstraint).WhenthesymmetryplaneisdefinedwiththeXSYMM,YSYMM,orZSYMMboundaryconditions,Abaqus/Standardwillautomaticallyadjustthenormalsofmastersurfacenodeswiththoseboundaryconditions(theadjustednormalwillbeparalleltothesymmetryplane).,FiniteSliding:SurfaceConsiderations(9/22),Mastersurfacesmoothingexample:ConcentrictubesPlanestrainconditionsareassumed;bothtubesaremadefromsteelwithE=207e3MPaandn=0.29.Theloadconsistsofaninternalpressure=1MPa.Theexactsolutionforthepressureattheinterfaceis0.4986MPa.,FiniteSliding:SurfaceConsiderations(10/22),Thesurfacesusedinthismodelareshownbelow.,FiniteSliding:SurfaceConsiderations(11/22),Contactpressurewhenouterisusedasmastersurface:,Themeancontactpressureisapproximately100toolarge.,FiniteSliding:SurfaceConsiderations(12/22),Contactpressurewheninnerisusedasmastersurface:,Thecontactpressureiszero!,FiniteSliding:SurfaceConsiderations(13/22),Whyistheresuchadifferencebetweenthetwosetsofresults?Theanswerhastodowiththemastersurfacesmoothing.In2D,themastersurfaceissmoothedthismeansthegeometryisalteredtoachieveasmoothlyvaryingsurface.Inthefollowingfigure,thedashedlinesrepresentthesmoothingusedinthecontactcalculations.WhilethisisnottheactualsurfacecreatedbyAbaqus,itofferssomeinsightintohowthesmoothandoriginallyfacetedsurfacesarerelated.,FiniteSliding:SurfaceConsiderations(14/22),Notethatthesmoothedsurfacedoesnottouchthenodesonthefacets.Considerthecasewherethemastersurfaceisouter.Giventhesmoothsurface,theslavenodes(frominner)areinitiallyoverclosed,givingrisetotheadditionalstressinthepart.,slavenodes:inner,FiniteSliding:SurfaceConsiderations(15/22),Now,considerthecasewherethemastersurfaceisinner.Giventhesmoothsurface,theslavenodes(fromouter)areinitiallyopen.Theappliedpressureisnotsufficienttoovercometheinitialclearanceproducedbysurfacesmoothing.,slavenodes:outer,FiniteSliding:SurfaceConsiderations(16/22),Now,editthemodeltosuppresssmoothing.Thenumericalsolutionisveryclosetotheanalyticalone(within5%).Wewilllaterrevisittothisexampletoseethesolutionobtainedwiththesmallslidingformulation.,Mastersurface:outer,FiniteSliding:SurfaceConsiderations(17/22),Usingthesurface-to-surfacediscretization,theresultsareinverycloseagreementwiththeanalyticalsolution(within5%)regardlessofthechoiceofmasterandslavesurfacewithoutanyadditionaluserintervention.,Mastersurface:outer,Mastersurface:inner,FiniteSliding:SurfaceConsiderations(18/22),Anothercommonissueforthenode-to-surfacediscretizationisthetendencyofslavenodestofalloffamastersurface(orgettrappedbehindit)Thisoccurswhenthemastersurfacedoesnotextendfarenoughtoaccountforallexpectedmotionsofthecontactingparts.Thisproblemislesslikelywiththesurface-to-surfacediscretization,becauseeachcontactconstraintisbasedonaregionoftheslavesurfaceratherthanindividualslavenodes.,Extensionsbeyondcornersaredesirableformastersurfacesinfinite-slidingproblemswithnode-to-surfacecontact.,FiniteSliding:SurfaceConsiderations(19/22),Abaqusmitigatesthisproblemintwoways:Surfacetrimming(freesurfacesonly)Removesconvexcornersneartheperimeterofanopensurface.Performedbydefaultexceptformastersurfacesinfinitesliding.ExtendedmastersurfacesAmastersurfaceusedinfinite-sliding,node-to-surfacecontactisextendedbasedonafractionoftheendsegmentorfacetedgelength.Thedefaultextensionfractionis0.1.,FiniteSliding:SurfaceConsiderations(20/22),ImplicationsoftrimmingMastersurfacesAutomaticallygenerated*mastersurfacesusedinfiniteslidingarenottrimmedbydefault(regardlessofthecontactdiscretizationmethodused).Byallowingtheextendedsurface,thepossibilityofaslavenodegettingtrappedbehindthemastersurfaceisreduced.Theprimarydisadvantageofnottrimmingthesurfaceisthatitaltersthecontactdirectionatacornerwhenusingthenode-to-surfacecontactdiscretization.,*Trimmingisprimarilyanissueforautomaticallygeneratedsurfaces;itisnotperformedbydefaultonanysurfacedefinedexplicitlyviaelementfaces(e.g.,modelscreatedinAbaqus/CAE).Youcanhowever,applytrimmingtothesesurfacesbyeditingtheinputfileandsettingTRIM=YESonthe*SURFACEoption.,FiniteSliding:SurfaceConsiderations(21/22),Exception:axisymmetricmastersurfacesshouldbetrimmedattheaxisofsymmetry.,CorrectMastersurfaceistrimmedalongtheaxisofsymmetry.Slavenodecannottravelalongtheaxis,andconstraintpreventsitfrombecomingtrappedbehindthemastersurface.,IncorrectMastersurfaceextendsalongtheaxisofsymmetry,soslavenodesarefreetotravelalongtheaxis.,mastersurface,FiniteSliding:SurfaceConsiderations(22/22),SlavesurfacesExtensionsbeyondcornersareundesirableforslavesurfaceswhenusingthenode-to-surfacecontactdiscretizationmethod.Theyintroduceextrasurfacearea,socontactstressesareincorrectattheendsofslavesurfaces.Thereisnoeffectoncontactareaforthesurface-to-surfacecontactdiscretizationmethod.Allautomaticallygeneratedslavesurfacesaretrimmedbydefault(regardlessofthecontactdiscretizationused).,SmallSlidingCharacteristics(1/4),Node-to-surfacediscretizationAbaqushasafairlycomplexalgorithmtoestablishtheslideplaneperslavenodebasedontheinitialconfigurationThesmall-sliding,node-to-surfacecontactdiscretizationmakesuseofinterpolatedmasternodalnormalsThesamemasternodesnearthe“anchorpoint”(X0inthefigure)takepartinloadtransferthroughouttheanalysisSlidingdistanceshouldremainlessthanfacetsizeevenforaflatmastersurfaceTheslideplanetranslateswiththe“anchorpoint”Ingeometricallynonlinearanalysestheslideplanewillalsorotatewiththemastersurface,Anchorpointandslideplaneforsmall-sliding,node-to-surfacecontact,SmallSlidingCharacteristics(2/4),ThemastersurfacenodalnormalvectorsareinvolvedinestablishingtheslideplanesfortheS-S,N-to-SformulationBydefault,theseareaveragedfromadjacentfacetnormalsOnlyfacetsthatarepartofthesurfacedefinitionareconsideredAutomaticallyconsiderssymmetryifsymmetryboundaryconditions(XSYMM,YSYMM,orZSYMM)areappliedtothemastersurfacenodesYoucanoverridethedefaultnodalnormalusingthe*NORMALoptionThisoptionisnotcurrentlysupportedbyAbaqus/CAE,butcanbeaddedviathekeywordeditor,SmallSlidingCharacteristics(3/4),Thesurface-to-surfaceversionofsmall-slidingcontactworkssimilarlySomedifferencesinLocationofanchorpointsSlideplanenormaldirectionsWhichmasternodesparticipateinconstraints(andassociatedconstraintcoefficients)ThesearchdirectionusedinthealgorithmtofindtheanchorpointusestheslavenormalratherthantheinterpolatedmasternormalRevertstothenode-to-surfaceformulationincaseswherethesurface-to-surfacesearchdoesnotseethemastersurface,SmallSlidingCharacteristics(4/4),IfAbaqusisunabletoestablishaslideplaneforaparticularslavenode.NocontactconstraintwillbeenforcedforthatslavenodeDiagnosticinformationinthedata(.dat)filefor*PREPRINT,CONTACT=YES:,SmallSliding:LocalContactPlane(1/11),Eachslavenodehasanassociatedcontactplanedefinedbytwofeatures:Theanchorpoint:Thecontactdirectionpointsfromtheanchorpointtotheslavenode.Theanchorpointforaslavenodewhenusingnode-to-surfacecontactisthepointonthemastersurfacewheretheinitialinterpolatednormalpassesthroughtheslavenode.Abaqus/StandardmustdefineasmoothlyvaryingnormalvectorN(x)alongthemastersurfacetodeterminetheanchorpoint.Thelocalcontactplaneorientation:Thelocalcontactplaneisorthogonaltothecontactdirection.,2,1,SmallSliding:LocalContactPlane(2/11),MastersurfacenormalvectorsUnitnormalvectorsareconstructedforeachnodeonthemastersurfacebyaveragingthenormalsofthesurfacefacetsconnectedtothenode.Theaveragednormalsatnodes2and3determinethesurfacenormalattheanchorpoint(X0).,Mastersurfacenormalvectors,SmallSliding:LocalContactPlane(3/11),Onlythefacetsthatarepartofthesurfacedefinitionareusedwhenconstructingthenodalnormalsforthemastersurface.Abaqus/Standardwillautomaticallytrimmastersurfacesusedinsmall-slidingcontactpairstopreventcornerextensionsfromcreatinginaccuratesurfacenormalsonthemastersurface.,SmallSliding:LocalContactPlane(4/11),ThesmoothlyvaryingnormalvectorN(x)alongthemastersurfaceisconstructedusingtheshapefunctionsoftheunderlyingelementsandtheunitnormalvectorsatthenodes,Ni.Youcanalsospecifythenormalatanynode,Ni,directlyusingthe*NORMALoptionto:Providemoreaccuraterepresentationofthesurfacegeometry.Helpavoidpotentialnumericalproblemswhenboundaryconditionsandcontactconstraintsconflict.The*NORMALoptionisnotcurrentlysupportedbyAbaqus/CAE;itmaybeaddedtoyourmodelviathekeywordseditor,however.Whenthesymmetryofastructureisconsideredinamodel,itisveryimportantthatthemastersurfacenormalsbedefinedcorrectlyalongthesymmetryplane.Whensymmetryboundaryconditions(XSYMM,YSYMM,orZSYMM)areappliedtothemastersurfacenodes,Abaqus/Standardadjuststhemastersurfacenormals.,SmallSliding:LocalContactPlane(5/11),AnchorpointTheanchorpointdeterminestheportionofthemastersurfacewithwhichaslavenodewillinteract.Thecontactdirectionpointsfromtheanchorpointtotheslavenode.Theanchorpointforaslavenodeisthepointonthemastersurfacewheretheinitialinterpolatednormalpassesthroughtheslavenode.,SmallSliding:LocalContactPlane(6/11),Thepositionoftheanchorpointrelativetothesurroundingnodesonthemastersurfaceisfixed.Forexample:,SmallSliding:LocalContactPlane(7/11),OrientationThelocalcontactplaneisorthogonaltothecontactdirection.Thisplanewillnotbethesameasthesurfaceoftheelementsifthemastersurfaceiscurved.IfNLGEOMisnotused,theorientationofthecontactplaneremainsfixedduringthestep.IfNLGEOMisused,theorientationofthecontactplanewillbeupdatedasthebodydeforms.,SmallSliding:LocalContactPlane(8/11),LoadtransferLoadistransferredbetweentheslavenodeandallmastersurfacenodesinvolvedinthedefinitionofthecontactplane.Aweightingschemeisusedtodistributetheforce,Fs,actingontheslavenodetothemastersurfacenodes.Forgeometricallynonlinearanalysis,iftheanchorpointislocatedatamasternode,theslavenodecantransferadditionalforcetoanymasternodethatsharesanadjacentfacetwiththatnode.Iftheanchorpointislocatedbetweennodes,theslavenodewilltransferforcestothenodesthatdefinethemastersurfacesegmentorfacet.,SmallSliding:LocalContactPlane(9/11),Example:Theanchorpointforslavenodesisnodebonthemastersurface.Ifscontactsb,Fs=-Fbandnoloadistransferredtonodesaorc.Inageometricallynonlinearanalysis,whensslidesawayfromb,nod