3d crack questions andanswers.docx
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3d crack questions andanswers.docx
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3dcrackquestionsandanswers
Hieverybody,
Ireadup moreon"crackpropagation"and"cohesiveelements"inAbaqus.Butiamstillstrugglingtomakeitrunandfranklyiamrunningoutoftime.Ihavegotonlytwomoredaystogetthemodelrunning...
Irecalltheproblemthatiwanttosimulate:
Apieceofrubber(hyperelasticneo-hokean)materialissubjectedtostaticuniaxialtensionuntillitfractures.Asyoucanseeintheattachedpicture,thereisinitiallynocrackinthegeometry.Howeverthereisasingularitythatislikelytobethecrackinitiationpoint.Andthecrackisgoingtopropagatealongthehorizontaldottedline.
IamusingAbaqusStandardtosimulatestaticcrackpropagation.
TobeginwithisketchedthegeometryinthePartmoduleandthenipartitionedthegeometrytocreateaninterfacethatisgoingtoplay theroleofthecrackpropagationline.Myideaisthatbymakinguseof"cohesiveelements"intheinterfaceicouldbeabletogetacrackpropagation.
SointhePropertyModuleicreateda"hyperelasticneo-hookeanmaterial"toaccountfortherubbermaterialoutsideoftheinterface.Ithencreatedtwosections:
-a"solidhomogeneous"sectiontoaccountforthehyperelasticmaterialoutsideoftheinterface(topandbottomregions)
-a"cohesivesection"withthesamematerialproperties(hyperelasticmaterial)as rubbertoaccountforthecrackpath...
IntheInteractionModuleididn'timposeanyconstraintontheinterfacefaces.Idon'treallyunderstandwhetherornotishouldmodifyorcreatesomethinginthisModule.
Indeed,ishouldprobablytrytoimposea"bond"constraintontheinterfacefacesandthensetafracturecriteriontoprogressivlydebondthetopandbottomregionsthroughoutthedeformationofthemodel...?
?
?
Buthowcouldandshoudildothat..?
Anyway,thenigottotheMeshModuleand triedtomeshtheinterface.Butwhenitriedtoruntheanalysisigotanerrormessagelike"someelementshavenoproperty".Anditturnsouttheseelementscorrespondexactlytotheelementslyingintheinterface.
PleaseletmeknowwhatwaswronginmymodelandshouldiproceedinthedifferentModules(Part,Property,Assembly,Stepetc...).
Regards,
Malik
eispiata(Materials)
19Nov088:
27
Hereisapictureofthemodelwithaninterfacesketchedtoaccountforthecrackpath.
Regards,
Malik
∙
iwb(Materials)
19Nov0810:
51
Hi,
asfarasIknow,ifyoudefineasolidsectionascrackpathusingamaterialdamagelawisonly
possibleinABAQUS/Explicit.Inyourcase,Iwouldusea
traction-separation-law.Thisisexplainedinsection
26.5.6Definingtheconstitutiveresponseofcohesiveelementsusingatraction-separationdescription
oftheusersmanual.Havealookatthesubsectiondamagemodeling!
Agoodsourceforinformationisthepaperof
G.AlfanoandM.A.Criseld
Finiteelementinterfacemodelsforthedelamination
analysisoflaminatedcomposites:
mechanicaland
computationalissues
Int.J.Numer.Meth.Engng2001;50:
1701-1736.
Youcanfollowthestepsbelowasastartingpointtoget
themodelrunning:
-Defineamaterialwithmaterialbehaviourelastic,type
traction-->definedamageinitiationcrit.-->define
damageevolutionlaw
-Createasectionother-->cohesive,chooseyourmaterial,
response:
traction-separation
-asignthesectiontoyourcohesivezone
Hopethishelps.
Marco
eispiata(Materials)
19Nov0812:
55
Hi,
Itookyouradvice.
Fortherubberpartidefinedanelasticbehaviour(smallstrainproblem)andaSolidHomogeneoussectionthatiassignedtothebottomandtopparts.
Thenidefinedasecondmaterial:
-Elastic-->Traction(E=200000AbaqusUnitSystem,Poisons'sration=0.45)
-DamageforTraction-SeparationLaws-->QuadsDamage
Thenacohesivesectionassociatedwiththissecondmaterialwasassignedtothethinlayeraccountingforthecrackpath.
Iused(static,General)Explicitsolver.ShouldiuseDynamicExplicitinstead?
IskippedtheInteractionModulebecauseibelievethereisnothingtodefineormodifyinthisModule.Andthenidefinedtheboundaryconditions(UniaxialTension)intheLoadModule.
Imeshedthewholemodelwiththeappropriatemesh.Sothemeshitselfshouldn'tbeaproblem.
Theanalysiscompletedsuccessfully.
Howevernocrackpropagationoccuredasyoucanseeinthepicture.IamdeeplysuprisedinthesensethatisetquitealowvaluefortheNominalstress.Hencethecrackshouldpropagateunlessthereissomethingthatimissedintheprocess.
Regardingthepicture,letmeknowwhatyouthinkaboutthe"nocrackpropagationoccurs"issue.
Iamlookingforwardtoyourcommentsandremarks!
Malik
Thanks,
Malik
∙
eispiata(Materials)
20Nov085:
44
Hello,
Ihavebeenworkingfortwodaysonmymodelandimadesomeprogressintheprocessofunderstanding"crackpropagation"modelinginAbaqusbutididn'tgetwhatiwaslookingfor.Indeednocrackpropagationoccured...Frown
Theideaistodefinethecracktipasthezonewhere σ22 (stresscomponentinthey-direction)ismaximum(seeattachedpicture).
Iexpectedthecracktopropagatealongthehorizontallinemadeupofcohevsiveelementsbydefiningthenormalnominalstress...
The"upper"and"bottom"materialislinearelastic(isotropic)andaccountsforarubberlikematerialinthecaseofsmallstrain.
The"interface"isdefinedaslinearelastic(traction)associatedwithaDamageforTraction-Separationlaw.
Iamtryingtofigureoutwhynocrackpropagationoccurs.
HerearethevaluesthatisetforintheMaterialModule
-theelasticpropertiesofrubber:
Youngmodulus=2,Poison'sratio=0.48
-theelasticpropertiesofthecohesivezone:
E=1000,G1=1andG2=1
-thedamageforTractionSeparationlaw(cohesivezone):
Nominalstress_normalmode=1
Nominalstress_firstdirection=1000,Nominalstress_2nddirection=1000.
Iamdoingitinahurrysoiprobablymissedsomeimportantpoints.MoreoveriamnotfamiliarwithFEMcrackpropagationsomyquestionsmightseemsillytosomeofyou...
Iamlookingforwardtoyourcommentsandremarks.
Regards,
Malik
iwb(Materials)
20Nov087:
15
HiMalik,
unluckilyI'moutofoffice,so
Ican'tcheckyoursettingswithABAQUS.
Therearetwothingsyoucancheckwithyour
model.First,thereisanoutputfieldvariable
calledsdegthatshowsthedegreeofdamagein
thecohesiveelement.Youcanalsocheckfor
quads(orsomethinglikethat)toseeifyour
damageinitiationcriterionworks.Second,
thereisabenchmarkexamplefromalfanofor
cohesiveelements.Iwouldtestthemodelwith
thisparameters,becausetheyaredefinitely
reasonable.Yourplotlooksreasonable.Ijustguess
yourdamageinitiationcrit.isnotmet.
Maybeyoushoulduseafinermeshalongthecrack
path.
Goodluck
Marco
eispiata(Materials)
21Nov083:
43
Hi,
Accordingtoyouthedamagecriterionisnotmet.
IamgoingtoworkonthisusingSDEG.
Mylastquestionismoreaboutthegeometryitself.
Indeedijustcreatedonesinglegeometrythatipartitionedtoaccountfortheinterface.Soibasicallycreatedonesinglepart.
ShouldicreateseparatepartsinsteadandtiethemwithaTIEconstraint?
Thanks,
Malik
eispiata(Materials)
21Nov088:
20
HiMarco,
Couldyousendmethearticle?
?
Thanks,
Malik
iwb(Materials)
23Nov085:
00
Hi,
actuallythisarticleiscopyrightedbywileypress.
Icannotpostithere.
Butyoucanfinditin
InternationalJournalforNumericalMethodsinEngineering
Volume50Issue7,Pages1701-1736
PublishedOnline:
26Jan2001
Itshouldbeavailableateverytechnicaluniversitylibrary
oryoucanorderitonline.
Toyourquestionabove,Ithinkit'snottheworstthingto
modelyourspecimenasonepartandpartitionit.Ifyoucangetafeasiblemeshingthiswayit'sperfect.UsingseveralpartsandcouplethemwithatieconstrainedisrealizedusuallybyintroducingLagrangemultiplierfunctionalswhichaddsadditionalcomputationalcosttoyoursystem.
Greetings
Marco
Howdy.
IhavebeenabletomodelacrackandgetaccurateSIFvalues...butdoesanyoneknowhowtopropagateacrackusingCAE?
Cheers.
johnsmith2(Mechanical)
2Nov0610:
19
Doyoumeanfatiguecrackgrowth?
da/dN?
Ithinkinabaqus,youcanmodelthedifferentcracklengthandfindtheJ-integralcorresponding.Then,usingfatiguecriteriontomakecomparsionwithexperimentalresults.
xerf(Mechanical)
2Nov0610:
42
ThecrackpropagationinABAQUSisbasedonthenodereleaseapproach.Youdefineapairofsurfacesinsimilarmannertocontactmodeling.Initiallythesurfacesarebonded.Asthepropagationcriterionisfulfilled(CODorcriticalstress)thenodesofthe2surfaceswillbereleased.
Thestepstomodelcrackpropagationareexplainedinthedocumentation.Forv6.5see
ABAQUSAnalysisUser'sManual ->7.9.3Crackpropagationanalysis
rwwillia(Structural)
2Nov0610:
55
I'mworkingwithastaticload(notcyclic). IwanttomodelthecrackpropagationsothatIcanplotaloadversuscrackgrowthcurve. Mycurrentmodelhasacirclularfacepartition(instance)aroundtheinitialcracktipsothatIcouldhavethecollapsedquarter-pointelements. Ifiguretheremustbesomewaytopropagatethecrackandhavethemeshmovewithi
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