正面碰撞仿真方法(Front Crash Simulation)

FrontCrashSimulationFrontCrashSimulationEngineeringTechnologyAssociates,Inc.(ETA)英文网站：中文网站：E-mail：bpeng@PengBingyuan,ETA-China,2005.3AgendaGeneralmodelingguidelinesLimitationsofthesimulationDesignConceptsforFrontalCrashFrontalcrashsimulationtechniquesInterpretationsofsimulationresultsPengBingyuan,ETA-China,2005.3GeneralModelingGuidelinesGeneralModelingGuidelinesPengBingyuan,ETA-China,2005.3VehicleModeling

VehicleModeling:Tendencytosinglehomogeneousmodelforall3majorimpacts(front,side,&rear);Automaticmeshingandintegrationofcomponent;Uniformmeshes

requirelessassumptionabouttheresponse(bucklingmode)ofthestructure;

Acarbodycontains20~25squaremetersofmetalsheetMeshSizeNumberofshellElementsNormalSize10*10200,000Weldnuggetsize5*5800,000averagethickness1*12,000,000PengBingyuan,ETA-China,2005.3VehicleModelingBIWModelBuildingProcess:ImportingCADData:CADdatacanbeimportedtoVPGdirectly;TheCADformat:UG,CATIA,Pro/E,IGESandsoon;CADdatamaybemodifiedwhenimported;SometimestheCADdatamustbeseparatedintoseveralparts;IftheCADdatais3-dimension,themiddlesurfaceshouldbetakenout;PengBingyuan,ETA-China,2005.3VehicleModelingBIWModelBuildingProcess:AutoMesh:

TopologyAutomeshingisanadvancedmeshingalgorithm;FewertriangularelementHigherqualityquadsFlangeBasedApproachAchieve92%perfectioninrelationshiptothegivencriteria

TheElementsizeisusualusing10*10,theminimumelementsizeshouldbecontrolled(>=5mm);Onflange,twoelementsorthreeelementsshouldbecreatedforlink;Whenmeshing,differentmaterialordifferentelementpropertyshouldbeincludedtodifferentpart;Ifthepartisarigidpartanditissymmetrical,thenitshouldbeseparatedtotwodifferentpart;SomepartcanbereplacedbyMasselement,butnomeshing;ForFoam,Rubblematerialshouldbemodeledassolidelements;Itisbestthatthereare250partsintheBIW.PengBingyuan,ETA-China,2005.3VehicleModelingBIWModelBuildingProcess:ModelCheck:

Whenmeshedbyautomeshtools,checkingelementqualityisrequirement;Followingqualitiesareusuallyused:AutoNormalBoundaryDisplayCheckOverlapCheckRigidLinkCheckElem.SizeCheckWarpageCheckFreeSurfaceCheckPenetration

Whencheckfailed,thefailedelementshouldberepaired.PengBingyuan,ETA-China,2005.3VehicleModelingBIWModelBuildingProcess:Somecriticalpartsforfrontimpact:FrontBumper(notincludingfacial);Foam;Rail(UpperandLower);

Subframe;EngineandTransmission;EngineMount;Rocker;Dash;A-PillarandB-Pillar;Floor;Tunnelandsoon;PengBingyuan,ETA-China,2005.3VehicleModelingSuspensionModel:

CreatedfromVPG:Selectthesuspensiontype;Getthesuspensionhardpoints;Givethespringstiffnessanddampercoefficient;Materialshavebeenassigned(mostofthemarerigid)whensuspensioncreated;Elementpropertyshouldbealsoadjustedaccordingtotheactualpartandthemassofthepart;Aftercreation,itshouldbetestedwithaload.Meshedwithplateorsolidelements:TheCADdatashouldalsobeneeded;Itcanbemeshedwithplateorsolidelements;Materialsandelementpropertiesshouldbeassigned;Themassofitshouldalsobeadjusted.PengBingyuan,ETA-China,2005.3VehicleModelingTireModel:

VPGtirecanbeused,ithasanairbagtosimulatethetirepressure;Fourtirescanbecreatedatthesametime;Whencreated,thetiredimensionshouldbeinput,sometimesthetirestiffnessshouldalsobeadjusted;Thelinkbetweentireandaxesofthecarhasalsobeencreatedautomatically;PengBingyuan,ETA-China,2005.3VehicleModelingCreateKindsofLinks:

Spotweld:onthecar,thereareabout5000spotweld;NodalRigidBody(RBE2):usuallyusedincarcrashsimulation;

SpotweldBeams(onnodesoronelements):itistheflexiblespotweld,butnotorsion;Solid(onnodesoronelements):itcanbetension,shearandtorsion;Constrainedspotweld:itcanonlylinktwonodes,alsoarigidlink;Enginemount:ItcanbeusedRigidlink;TheSpringcanalsobeused;*CONSTRAINED_RIGID_BODIEScanbeusedtolinktworigidbodies;NodalRigidBodycanbeusedtolinkSuspensionandBIW:PengBingyuan,ETA-China,2005.3VehicleModelingDefineMaterialandElementProperty:Materialsparametersandelementsthicknessareprovidedbyuser;Thematerialsareveryimportanttothesimulationresults;DifferentmaterialsshouldbeselecteddifferentmaterialtypesinLS-DYNA;Differentelementtypesshouldbeselecteddifferentsectiontypes;Mostoftheelementformulationsareusedthedefaultvaluesexceptthattheyneededtobecontrolledthehourglass.

PengBingyuan,ETA-China,2005.3VehicleModelingPlacetheDummyModel:IfaDummyisneeded,

thenthechairmodelandthesteeringcolumn(sometimetheIP)shouldbealsomeshed;UsuallyusetheLSTCRigid50%orDeformable50%dummyinVPG;PlacethedummyaccordingtotheHpoint;Thedummyshouldalsobeadjustedtoasuitableposition;Whenpositionthedummy,asuitablenode/elementnumbershouldalsobegiven;Aseatbeltshouldalsobecreatedatthesametime.PengBingyuan,ETA-China,2005.3VehicleModelingDefinetheContact:TheCarBody:

Usuallyonecontactisdefined(*CONTACT_AUTOMATIC_SINGLE_SURFACE),onlyslavesurfaceisdefined;Ifthereispenetrationbetweenpartswhensimulating,thentheextracontactbetweenthesepartsshouldbedefinedafterterminateLSDYNA(Usually*CONTACT_AUTOMATIC_NODE_TO_SUFACEor*CONTACT_AUTOMATIC_SURFACE_TO_SURFACEisdefined);Cartowallandground:*RIGIDWALL_,itcanbecreatedautomaticallywhenusingstep-by-stepmethodinVPG.Glueandthecarbody:*CONTACT_TIED_SURFACE_TO_SURFACE;Thecontactbetweendummyandcarorseatbeltanddummyarealsodefinedautomatically;ControlNegativeVolume:

Firstcreateanullshellelementanddefineitinsinglesurfacecontact;Using*CONTACT_INERTIORtocombatthenegativevolume;PengBingyuan,ETA-China,2005.3MassDistributioninVehicleModelTotalvehicleMass1200kgDetailCarBody200kg100,000elements100,000nodes2gram/nodePowertrain200kgmeshedChassis&Wheels200kgmeshedComponents600kgAddedMassFor600masspoints:1kg/node

ControlthewholeMass:Non-structuralcomponentsaremodeledwithaprecisionthatis2ordersofmagnitudelowerthanthecarbodyitselfItisimportanttocarefullyconsiderthecomponentsthatmoverelativetothecarbodysuchasexhaustsystem,fueltank,seats,dummies,etc.PengBingyuan,ETA-China,2005.3VehicleModelingCreateFrontimpactmodel:Gotomenu/Safety/Crashworthiness/FMVSS208Frontimpactor/Safety/Crashworthiness/ECE94tocreatedthefrontimpactmodel;Theimpactorinformationshouldbeinputontheprompttable;Theinitialvelocityofthecarisalsodefinedautomaticallywhenusingthismethod;Tworigidwallor40%deformablebarrierarealsodefinedautomatically;Thecontactbetween40%deformablebarrierandthecarbodyisdefinedautomatically;PengBingyuan,ETA-China,2005.3VehicleModelingDefineoutputdataandcontrolcards:

SomeControlCards:*CONTROL_CONTACT,*CONTROL_SHELL,*CONTROL_PARALLEL,*CONTROL_OUTPUT,*CONTROL_ENERGY,*CONTROL_TERMINATION,*CONTROL_TIMESTEP

andsoon;SomeDatabaseCards:*DATABASE_HISTORY_NODE,*DATABASE_HISTORY_BEAM,*DATABASE_BINARY_D3PLOT,*DATABASE_BINARY_D3DUMP,*DATABASE_RCFORC,*DATABASE_RWFORC,*DATABASE_MATSUMandsoon;

SomeAccelerometer:*ELEMENT_SEATBELT_ACCELEROMETER;SomeSectionForcecard:*DATABASE_CROSS_SECTION_PLANEPengBingyuan,ETA-China,2005.3GeneralMeshGuidelinesINumbering:Elementsandnodesshouldbenumberinginaccordancetocompanynumberingsystem(BIW,closures,powertrain,suspensions,seats,dummies,etc.)Parts,materials,sectionpropertiesshouldbenumberinginaccordancetocompanynumberingsystemElementQualityRequirements:PengBingyuan,ETA-China,2005.3GeneralMeshGuidelinesIITotaltriangleelementsshouldbelessthan10%,incriticalpartsthetriangleelementsshouldbelessthan5%

Inlargedeformation,highstresszoneshouldbe<=10mmInlargesheetpartsthathavesmallcurvature,fewfeatures,andfewattachments(roof,windshield),elementsizecouldbeaslargeas100mmSmallestelementlengthmustbe>=5mmNofreerigidconnections,doubledependentconnectionsAppropriatelocationofvehicleC.G.shouldbeachievedinFEmodelShellelementsshouldbemodeledinthemiddlesurfaceoflinedataNoinitialpenetrationsPengBingyuan,ETA-China,2005.3GeneralMeshGuidelinesIIIHoleswithdiameter>6shallbecreated,smallerholesshallbedeleted(meshcreationwithfill-in)HoleShapes:Plug,screw,andrivetholesshallbedeleted,fillinholeonclips,andplaceNODESatcenterofholes.Theflangeofflangedholesandedges:

DiameterShapeφ6.1~20Squareφ21~25Hexagonφ26~32Octagon3~5mmGeometryMesh5mm<3mmGeometryMeshPengBingyuan,ETA-China,2005.3GeneralMeshGuidelinesIVSwagesGeometryMeshSwageswithdepth>5mmSwageswithdepth<5mm

andwidth>5mmGeometryMeshGeometryMeshSwageswithdepth>5mm

andwidth<5mm

Ifpossible,place3elementspershapeoftheswagesectionPengBingyuan,ETA-China,2005.3ModelingofSpotweldsINodetonodeconnectionsNodalrigidbodyWeldednodesetsSpotweldelementsDiscretebeamsWeldshouldbeorthogonaltotheflanges,whichrequirescorrespondingmeshesinbothflangesSkewedweldsmayweakenthestructurebyrigidbodyrotationMaypromotehourglassing2elementsintheflangetopositiontheweldcentrallyPengBingyuan,ETA-China,2005.3ModelingofSpotweldsIIElementtoelementconnectionsBeamelementtype9,materialtype100Slidinginterfacetype7Typicallyhasheightof1mmanddiameterof6mmGenerallywilladdmassthatisreportedin“d3hsp”fileUsuallyinfluencethetimestep3elementsintheflangetopositiontheweldcentrallyElementsizeshouldbeaboutequaltotheweldnuggetdiameterMaycausebadwelddefinitionduetoinaccurateCADdataandautomaticweldgeneration6mm1mmt=L/C=0.2sPengBingyuan,ETA-China,2005.3LimitationsoftheSimulation

LimitationsoftheSimulationPengBingyuan,ETA-China,2005.3LimitationofCAE/FEASimulationIDifferencebetweentestandcalculationresultshavemanydifferentcauses;suchasinthematerialdescriptionofbodypanelsTheoryandnumericalimplementation

ofplasticityformildsteelandothermetalsHardeningandrate

dependencyparametersformildsteelandothermetalsMaterialvariability(initialanisotropy/formingprocess/thermaltreatment)Initialstresses/strainandthinningaredifficulttoaccountforinthesimulationPengBingyuan,ETA-China,2005.3LimitationofCAE/FEASimulationIIRuptureofmaterialsandcrackpropagation(enginemounts?)isdifficulttopredict

RaptureofconnectionsaredifficulttomodelRealisticfrictionmodelsaremissingBehaviorofnon-steelcomponentsCoarsemeshesallowonlycurvaturebucklingmodesRefiningmeshgenerallywillsmooththedeformedshape,reducethehourglassandcontactenergyproblemsPengBingyuan,ETA-China,2005.3DesignConceptsforFrontalCrashDesignConceptsForFrontalCrashPengBingyuan,ETA-China,2005.3ConceptofVehicleStructureDesignIEnergyAbsorptionZoneForwardandrearwardsectionsMaximumenergyabsorptionofthevehiclekineticenergyUndergolargeplasticdeformationsMaintainforcelevelsSafedecelerationrates(crashpulse)throughoutthedeformationExhibitinghighductilityandlesstendencytofracture(30~40%strain)PassengerCompartmentIntegrityProvidesafetyzonetooccupantsMinimizetheintrusionfromEnergyAbsorptionZones

EnergyAbsorptionEnergyAbsorptionPassengerCompartment

IntegrityPengBingyuan,ETA-China,2005.3ConceptofVehicleStructureDesignIIEnergyAbsorbZonedividestothreeCrushZonesFrontSoftzonereducetheaggressivelyonpedestrian-to-vehiclecollisionsPrimaryStifferzoneForesectionofthepowertraincompartmentMainenergyabsorbingstructure“Axial”crashmodeisdesiredtoabsorbthemostenergySecondaryStifferZoneStructureinterfacebetweentheabsorberandcompartmentMaypresentpotentialhazardtotheoccupantsAvoidexcessiveloadconcentrationsCombinationof“axial”and“bending”modesThelengthofthesetwostifferzonesvarywiththelocationandmountingofthepowertrainandsuspensionsystems

PengBingyuan,ETA-China,2005.3ConceptofVehicleStructureDesignIIIPassengerCompartmentplayskeyroleinoccupantprotectionHavestructuralstrengthforomni-directionalcollisionmodesHingepillar:

longitudinalloadfromfrontalcollisionLateralloadfromsideimpactAPillar:Transferloadto“greenhouse”forfrontalcollisionResistthecollapseduringrolloverShouldkeeptheoccupantinsidethevehiclestructureduringimpactStiffandwelldesigntotransfertheimpactloadandavoidstructuredeformationPengBingyuan,ETA-China,2005.3ComponentDesign

CollapseModesAxialcollapseThemosteffectivemechanismforenergyabsorptionPerhapsthemostdifficultonetoachieveinrealstructuresbecauseoftheinstabilityproblemsassociatedwithit.BendingcollapseAlowerenergymodeAfront-endstructurewillalwayshaveatendencytocollapseinthistypeofmodeMoststructurememberswillexhibitmixedmodescomprisedofaxialcollapseandbending.BendingModeAxialModePengBingyuan,ETA-China,2005.3SideMembersDesignShouldcollapseprogressivelyinapredeterminedmode

RelativelystifftominimizethetendencytowardsstructureinstabilityandbucklingduringcrashShouldavoidworkhardeningmaterialsthatwillledtohighdecelerationpeaksandincreasethestructureinstabilityMayneedsomespecialdesignssuchas“beads”tocontrolthecrashmodesProvideastableplatformforthecollapsingenergyabsorbersandtotransfertheseloadsasefficientlyaspossiblePengBingyuan,ETA-China,2005.3FrontalCrashDesignVehiclewillcrash500~850mmEnergyabsorptionisprimarilycontrolledbythebehavioroffoursidemembers:

Twolongitudinal

rails

Twouppersiderails(shortguns)Use“closed”sectionsinthesesidemembers“Good”designshouldcollapsetheserailstoonefourthoftheiroriginallengthDesignedtodevelopandmaintainforcelevelsDesignedtodeceleratethevehiclewithinthetoleranceofoccupant(crashpulses)CarefullyselectthedesiredcrushsequenceandmodesPengBingyuan,ETA-China,2005.3TypicalEnergyAbsorptionandcrossSectionForcePengBingyuan,ETA-China,2005.3TypicalCrashShapeandIntrusionsPengBingyuan,ETA-China,2005.3CrashPulsesPengBingyuan,ETA-China,2005.3FrontCrashSimulationTechniquesFrontCrashSimulationTechniquesPengBingyuan,ETA-China,2005.3ModelingIFollowGeneralModelingGuidelinesModelVehiclePartCompleteBIW,includingwindshield(RefinedmeshbeforeB-Pillar)Bumpersystemincludinglowspeedenergyabsorbingsystem(foam),ignorefasciaandnon-structurecomponentsFrontdoors(withsideglass)Engineandtransmission(rigidshells)andmountingcomponentsExhaustSystem(innearengineareaifinteractionwithstructure)FrontsuspensionandsubframecomponentsRearaxleanddriveshaft(forreardrivevehicles)CondenserandRadiatorSteeringSystemInstrumentPanelBeamBrakeBoosterOthercomponentslikeinstrumentationifavailableMass–MatchtotalmassandvehicleC.G.PengBingyuan,ETA-China,2005.3AssumptionsSpotweldsfailuregenerallyisnotconsideredMaterialvariation,residuestress,andthinningisnotconsideredStrainrateeffectsmaybeincludedifavailableMaterialtearingisnotincludinginthesimulationIgnoregeometrydetails(Generalmodelingguidelines)Neglectwrinkles,tearsandnon-designedfeaturesCertaincomponentsareassumedtoberigidUnbreakableboltconnectionsIgnoreinsignificantcomponents(fenders,bumperfascia,trims,etc.)CoefficientoffrictionsisassumedtobethesameRigidwallsaregenerallyassumedtobeperfectlyrigidPengBingyuan,ETA-China,2005.3ASCIIandBinaryOutputsIGlobalStatistics(“glstat”)MaterialSummary(“matsum”)CrossSectionForce(“secforc”)LeftandrightrockersatfrontdooropeningLeftandrightroofrailsatfrontdooropeningLeftandrightdoorbeltlineforfrontdoorsLeftandrightmotorcompartmentrailsatshocktower(Leftandrightrailsforwardof#1crossmemberforbodyonframevehicles)Leftandrightupperrailsatshocktower(Leftandrightrailsforwardof#2crossmemberforbodyonframevehicles)Leftandrightlongitudinalrailsattheheelhard(LeftandrightrailsforeandaftofTorqueboxforbodyonframevehicles)DriveshaftforrearwheeldrivevehiclesOthersectionsthatmaybeofinterest.PengBingyuan,ETA-China,2005.3ASCIIandBinaryOutputsIITimeHistory(“nodout”)LeftandrightrockerinnerpanelsatcenterofreardooropeningLeftandrighttoepanatcenterlineoftheoccupants,100mmabovetheleveloffloor;andtwocorrespondingpointsintherearstructurewithsameYandZTwopointsatcenterlineofIPbeamandtwocorrespondingpointsintherearstructurewithsameYandZApointatcenterofsteeringwheelandacorrespondingpointintherearstructurewithsameYandZTopandbottomofengineOtherpointsofinterestRigidWallForce(“rwforc”)DiscreteElementForce(“deforc”)RigidBodyMotion(“rbdout”)JointForce(“jntforc”)Plotfiles(“d3plot”)PengBingyuan,ETA-China,2005.3SimulationQualityCheckThesimulationtimestepisnottoosmalltocausebigmassscaling

(<2%),

Criticalpartsinthecrashzoneshouldbecheckforthemassscalingandtheaddedmassforthesepartsshouldbelessthan1%.

Totalenergyshouldremainnearlyconstant(0.98~1.02).Hourglassenergyshouldbelessthan5%ofthetotalenergy.Thereshouldnotbeanddiscontinuousjumpsorspikesinanyoftheenergycurves.Crushpatternofbumpersystem,rails,andunderbodystructureshouldbereasonable.NolooseconnectionsNostackupofcomponentstobarrierfaceandtoothercomponents.Penetrationofonepartintoanother.Penetrationofanynodethroughrigidwalls.Forcesindiscreteelementsshouldbereasonable.PengBingyuan,ETA-China,2005.3SimulationCorrelationTestsThesimulatedvehicleshouldhasthesameconstructionandconfigurationastestvehicleRearrockervelocity,displacement,andeffectiveacceleration.Crushpatternofrailsandunderbodystructure(visuallycomparetestfilmwithanimation).Crushpatternoffrontbodyhingepillaranda-pillar(visuallycomparetestfilmwithanimation).Crushpatternofdoor(Visuallycomparetestfilmwithanimation).Crushpatternofdash(Visuallycomparetestfilmwithanimation).Enginedisplacementandvelocity(visuallycomparedeformedvehicletosimulationresults,alsocomparetheaccelerometeroutputtosimulation),Enginetodashcontact(Visuallycomparetestfilmwithanimation).Brakeboostertoshocktoweranddashcontact(Visuallycomparetestfilmwithanimation).Steeringcolumnmotion(Comparetestmeasurementswithsimulationoutput).Toepanintrusion(Comparetestmeasurementswithsimulationoutput).Alltestingfilms,acceleration/velocity/displacementmeasurementsandpicturesshouldbepresentedinordertodoacompletecorrelation.PengBingyuan,ETA-China,2005.3InterpretationoftheSimulationResultsInterpretationoftheResultsPengBingyuan,ETA-China,2005.3ModelInformationandDeformedShapes

HalfVehicleModel

<6,000ElementsDemotheFrontalCrash

PhenomenaDemotheinterpretation

ofthesimulationResultsPengBingyuan,ETA-China,2005.3DeformedModeITwophasesseparatedbyengineimpacttherigidWallEngineCompartmentstructure(sidemembers)deformed(<32ms)Thefrontpartofsidemembercollapsedat10msSidemembercollapsesinbendingmodeafterthatFrontofcabindeformed

(>32ms)Engine/transmissioncontactwithsuspensionmountat38msHighestdecelerationat38msPengBingyuan,ETA-China,2005.3DeformedModeIISubsystemsDeformationMechanismTimeSideMemberandBumperForceinputfrombumperactsonfrontpartofsidemember0~5msFrontpartofsidememberdeformsinaxialmode5~10msSidememberdeformsinbendingmode10~32msEngineer/TransmissionEngine/transmissionreachesbarrier32msEngine/transmissioncomesincontactwithsuspensionmount38msLowerDashStructureFrontpartoffloortunneldefo