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1、HeliusMCTv2forAbaqusExampleProblemPage8of22ValueNormalizedNormalizedNormaIizedpsi(ij/11)(ij/22)(ij/12)11267,057100.0%1015.6%1575.6%2225,5409.6%100.0%150.7%333,6231.4%14.2%21.4%1216,9496.3%66.4%100.0%131,2740.5%5.0%7.5%239320.3%3.6%5.5%StressComponentFigUre5:StressstateofselectedelementPage9of22El.3.
2、2FirstFailureAnaIySiSsafirstattemptataprogressivefailureanalysis,athrough-thicknessmeshdensityof1elementperfacesheetand1elementforthecore,foratotalof3elementsthroughthethicknessofthesandwichconstructionisused.Inthiscase,theC3D8R(reducedintegrationelement)isused.Notethatitispossibletouseasingleelemen
3、tthroughthethicknessoftheentirelaminatedsandwichstructure;however,duetotherelativelyhighcomplianceofthethickfoamcore,theuseofasingleelementthroughthelaminatethicknessyieldsveryinaccurateresults.Model(三)IelemFaceIelemCore.inpElementtype:C3D8RThrough-thicknessmeshdensity:oCompositeHacesheets:1elemento
4、FoamCore:1elementResultsTable2displaystheloadlevelatwhicheachtypeoffailureeventispredicted.ThecriteriausedtopredictlocalizedmatrixfailureandlocalizedfiberfailurearedescribedindetailintheHelius:MCTTheoryManual.InTable2,itshouldbeemphasizedthatthematrixfailureandfiberfailureloadlevelsindicatetheloadat
5、whichalocalizedmatrixorfiberfailureisfirstdetected.NotethatthisfirstinstanceofmatrixfailureorfiberfailureoccursatasingleGaussianintegrationpointwithinoneofthematerialpliesofoneoftheelementsofthemodel.Inalargecompositestructurecontainingthousands(ormilions)ofGaussianintegrationpoints,averylargenumber
6、oflocalizedconstituentfailuresarenecessaryinordertodetectanyappreciablechangeintheoveral1stiffnessofthecompositestructure.Globalstructuralfailurecanbedefinedinmanydifferentways,butforthepurposeofthisexampleproblem,globalfailureisdefinedasalargediScontinuityinthecompositestructuresoveral1verticalload
7、-displacementcurve.TheoverallverticaldeformationofthecompositestructureisquantifiedbyusingtheverticaldisplacementattheloadapplicationpointlabeledOinFigure1.Becausetheloadheadandadapterareconsideredrigid,alargediscontinuityintheload-displacementcurveisindicativeofveryrapidgrowth(spreading)oflocalized
8、materialfailuresthatoccurduringaparticularloadincrement,resultinginalargedegradationoftheoveral1stiffnessofthecompositestructure.Thisdefinitionofglobalstructuralfailureischosensincemostexperimentaltestsarestoppedatthispointtopreventdamagetoexpensivetestequipment.Figure6showstheoveral1verticalload-de
9、flectioncurveforthecompositestructure.Notethattheoverallresponseofthestructureappearstobelinearuptoaloadlevelof56%,atwhichtimeaglobalstructuralfailureoccurs.AsseeninTable2,thefirstlocalizedmatrixfailureoccurredataloadof49%andthefirstlocalizedfiberfailureoccurredataloadof49%.However,allofthelocalized
10、failuresthatoccurredbetweentheloadrangeof49%and56%werenotsufficienttoproduceavisuallydetectablechangeinthecompositestructuresoverallload-deflectionresponse.Whentheloadisincreasedfrom56%to57%,averylargecascadeoflocalizedfailuresoccurs.Thisfailurecascadeissignificantenoughtodestroyapproximately92%ofth
11、everticalstiffnessofthecompositestructure(theverticaldisplacementincreasesbyafactorof12duringtheloadincrement).Thistypeofbehavior,wheretheoverallresponseofthecompositestructureremainsapproximately1inearuptoglobalstructuralfailureisfairlycommonamongstructurescomposedofbrittlecompositecapturestheentir
12、elayup(3elementsthrough-thickness).1stmodification:Increasethecoremeshdensitytoallow4elementstocapturethecoreprofile(6elementsthrough-thickness).2ndmodification:Increasethefacesheetdensitytoa11ow2elementstocapturethelayupofeachfacesheet(8elementsthrough-thickness).3rdmodification:Increasethefaceshee
13、tdensitytoallow4elementstocapturethelayupofeachfacesheet(12elementsthrough-thickness).Ideally,averyfinethrough-thicknessmeshwouldbeutilizedtoprovidethemostaccurateloadingdistributionanddeformationthroughoutthemodel,butruntimecostsoftenlimitmeshdensities.Model(三)1e1emFace_4e1emCore.inpElementtype:C3D
14、8RThrough-thicknessmeshdensity:ofacesheets:1elementocore:4elements2elemFace_4elcmCore.inpElementtype:C3D8RThrough-thicknessmeshdensity:ofacesheets:2elementsocore:4elements4e1emFace_4elemCore.inpElementtype:C3D8RThrough-thicknessmeshdensity:ofacesheets:4elementsocore:4elementsPage12of22ResultsTable3d
15、isplaystheloadlevelatwhicheachtypeoffailureeventispredictedbythefourmodels.Figure7displaystheoverallverticalload-displacementcurvesfortheresultofthistrendisthatthemagnitudeofthepeakin-plancstressestendstodecreaseasthethrough-the-thicknessmeshdensityisincreased,thuslocalizedfailureispredictedtooccura
16、thigherloadlevels.2.Globalfailureisonlyslightlyaffectedbymeshdensity.-Despitethefactthatincreasingthethrough-the-thicknessmeshdensityresultsindelayedlocalfailureinitiationforboththematrixandthefiber,thepredictedglobalstructuralfailureloadisnotsignificantlyaffectedbythethrough-the-thicknessmeshdensit
17、y.Thisobservationsuggeststhattheescalationfromlocalfailureinitiationtoglobalstructuralfailureoccursfasterasthethrough-the-thicknessmeshdensityisincreased.Itisreasonabletoexpectlocalfailurestoprogressintoglobalfailuresmorerapidlyforahigherdensitymesh(asseeninTable3).Adensermeshresultsinamorerefinedfa
18、ilurepathforastructureduetotheincreaseinnumberofGaussianintegrationpointsforfailurecriteriontobeevaluatedat.morerefinedfailurepathfacilitatesamorerapidprogressionoffailure,hencetherapidprogressionoflocalfailuresintoglobalfailures.Page14of22El.3.4EffectofElementTypeonProgressiveFailureResponseTheprogressivefailureresponseofthecompositestructurewas
