汽车安全气囊碰撞有限元分析外文翻译.docx

汽车安全气囊碰撞有限元分析外文翻译.docx

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汽车安全气囊碰撞有限元分析外文翻译

FINITEELEMENTANALYSISOFAUTOMOBILE

CRASHSENSORSFORAIRBAGSYSTEMS

ABSTRACT

Automobilespringbiascrashsensordesigntimecanbesignificantlyreducedbyusingfiniteelementanalysisasapredictiveengineeringtool.Thesensorsconsistofaballandspringscasedinaplastichousing.Twoimportantfactorsinthedesignofcrashsensorsaretheforce-displacementresponseofthesensorandstressesinthesensorsprings.Inthepast,sensorsweredesignedbybuildingandtestingprototypehardwareuntiltheforce-displacementrequirementsweremet.Prototypespringsneedtobedesignedwellbelowtheelasticlimitofthematerial.Usingfiniteelementanalysis,sensorscanbedesignedtomeetforcedisplacementrequirementswithacceptablestresslevels.Theanalysisprocedurediscussedinthispaperhasdemonstratedtheabilitytoeliminatemonthsofprototypingeffort.

MSC/ABAQUShasbeenusedtoanalyzeanddesignairbagcrashsensors.Theanalysiswasgeometricallynonlinearduetothelargedeflectionsofthespringsandthecontactbetweentheballandsprings.Bezier3-Drigidsurfaceelementsalongwithrigidsurfaceinterface（IRS）elementswereusedtomodelball-to-springcontact.Slidelineelementswereusedwithparallelslidelineinterface（ISL）elementsforspring-to-springcontact.

Finiteelementanalysisresultsfortheforce-displacementresponseofthesensorwereinexcellentagreementwithexperimentalresults.

INTRODUCTION

Animportantcomponentofanautomotiveairbagsystemisthecrashsensor.Varioustypesofcrashsensorsareusedinairbagsystemsincludingmechanical,electro-mechanical,andelectronicsensors.Anelectro-mechanicalsensor（seeFigure1）consistingofaballandtwospringscasedinaplastichousingisdiscussedinthispaper.Whenthesensorexperiencesaseverecrashpulse,theballpushestwospringsintocontactcompletingtheelectriccircuitallowingtheairbagtofire.Theforce-displacementresponseofthetwospringsiscriticalindesigningthesensortomeetvariousaccelerationinputrequirements.Stressesinthesensorspringsmustbekeptbelowtheyieldstrengthofthespringmaterialtopreventplasticdeformationinthesprings.Finiteelementanalysiscanbeusedasapredictiveengineeringtooltooptimizethespringsforthedesiredforce-displacementresponsewhilekeepingstressesinthespringsatacceptablelevels.

Inthepast,sensorsweredesignedbybuildingandtestingprototypehardwareuntiltheforcedisplacementrequirementsweremet.Usingfiniteelementanalysis,thenumberofprototypesbuiltandtestedcanbesignificantlyreduced,ideallytoone,whichsubstantiallyreducesthetimerequiredtodesignasensor.Theanalysisprocedurediscussedinthispaperhasdemonstratedtheabilitytoeliminatemonthsofprototypingeffort.

MSC/ABAQUS[1]hasbeenusedtoanalyzeanddesignairbagcrashsensors.Theanalysiswasgeometricallynonlinearduetothelargedeflectionsofthespringsandthecontactbetweentheballandsprings.Variouscontactelementswereusedinthisanalysisincludingrigidsurfaceinterface（IRS）elements,Bezier3-Drigidsurfaceelements,parallelslidelineinterface（ISL）elements,andslidelineelements.Thefiniteelementanalysisresultswereinexcellentagreementwithexperimentalresultsforvariouselectro-mechanicalsensorsstudiedinthispaper.

PROBLEMDEFINITION

Thekeycomponentsoftheelectro-mechanicalsensoranalyzedaretwothinmetallicsprings（referredtoasspring1andspring2）whicharecantileveredfromarigidplastichousingandasolidmetallicballasshowninFigure1.Theplastichousingcontainsahollowtubeclosedatoneendwhichguidestheballinthedesireddirection.Theballisheldinplacebyspring1attheopenendofthetube.Whenthesensorisassembled,spring1isinitiallydisplacedbytheballwhichcreatesapreloadonspring1.Theballisabletotravelinonedirectiononlyinthissensorandthisdirectionwillbereferredtoasthex-direction（seetheglobalcoordinatesystemshowninFigure2）inthispaper.Onceenoughaccelerationinthex-directionisappliedtoovercomethepreloadonspring1,theballdisplacesthespring.Astheaccelerationappliedcontinuestoincrease,spring1isdisplaceduntilitisincontactwithspring2.Once

Figure1.Electro-mechanicalautomobilecrashsensor.

contactismadebetweenspring1andspring2,anelectriccircuitiscompletedallowingthesensortoperformitsfunctionwithintheairbagsystem.

FINITEELEMENTANALYSISMETHODOLOGY

Whencreatingafiniteelementrepresentationofthesensor,thefollowingsimplificationscanbemade.Thetwospringscanbefullyrestrainedattheirbasesimplyingaperfectlyrigidplastichousing.Thisisagoodassumptionwhencomparingtheflexibilityofthethinspringstothestiffplastichousing.Theballcanberepresentedbyarigidsurfacesinceittooisverystiffascomparedtothesprings.Ratherthanmodelingthecontactbetweentheplastichousingandtheball,allrotationsandtranslationsarefullyrestrainedexceptforthexdirectionontherigidsurfacerepresentingtheball.Theserestraintsimplythatthehousing

Figure2.Electro-mechanicalsensorfiniteelementmesh.

willhavenosignificantdeformationduetocontactwiththeball.Theserestraintsalsoignoreanygapsduetotolerancesbetweentheballandthehousing.Theeffectoffrictionbetweentheballandplasticisnegligibleinthisanalysis.Thesensorcanbeanalyzedbyapplyinganenforceddisplacementinthex-directiontotherigidsurfacerepresentingtheballtosimulatethefulldisplacementoftheball.Contactbetweentheballandspringsismodeledwithvariouscontactelementsasdiscussedinthefollowingsection.Anonlinearstaticanalysisissufficienttocapturetheforce-displacementresponseofthesensorversususingamoreexpensiveandtimeconsumingnonlineartransientanalysis.Althoughthesensorisdesignedwithaballmassandspringstiffnessthatgivesthedesiredresponsetoagivenacceleration,thereisnomassassociatedwiththeballinthisstaticanalysis.Themassoftheballcanbedeterminedbydividingtheforcerequiredtodeflectthespringsbytheaccelerationinputintothesensor.

Mesh

ThefiniteelementmeshforthesensorwasconstructedusingMSC/PATRAN[2].ThesolverusedtoanalyzethesensorwasMSC/ABAQUS.ThefiniteelementmeshincludingthecontactelementsisshowninFigure2.Theplastichousingwasassumedtoberigidinthisanalysisandwasnotmodeled.Bothspringsweremodeledwithlinearquadrilateralshellelementswiththinshellphysicalproperties.TheballwasassumedtoberigidandwasmodeledwithlineartriangularshellelementswithBezier3-Drigidsurfaceproperties.

Tomodelcontactbetweentheballandspring1,rigidsurfaceinterface（IRS）elementswereusedinconjunctionwiththeBezier3-Drigidsurfaceelementsmakinguptheball.LinearquadrilateralshellelementswithIRSphysicalpropertieswereplacedonspring1andhadcoincidentnodeswiththequadrilateralshellelementsmakingupspring1.TheIRSelementswereusedonlyintheregionofballcontact.

Tomodelcontactbetweenspring1andspring2,parallelslidelineinterface（ISL）elementswereusedinconjunctionwithslidelineelements.LinearbarelementswithISLphysicalpropertieswereplacedonspring1andhadcoincidentnodeswiththeshellelementsonspring1.Linearbarelementswithslidelinephysicalpropertieswereplacedonspring2andhadcoincidentnodeswiththeshellelementsmakingupspring2.

Material

Bothspring1andspring2werethinmetallicspringsmodeledwithalinearelasticmaterialmodel.Nomaterialpropertieswererequiredforthecontactorrigidsurfaceelements.

BoundaryConditions

Bothspringswereassumedtobefullyrestrainedattheirbasetosimulatearigidplastic

housing.Anenforceddisplacementinthex-directionwasappliedtotheball.Theballwasfullyrestrainedinallrotationalandtranslationaldirectionswiththeexceptionofthexdirectiontranslation.BoundaryconditionsforthespringsandballareshowninFigure2.

DISCUSSION

Typicalresultsofinterestforanelectro-mechanicalsensorwouldbethedeflectedshapeofthesprings,theforce-displacementresponseofthesensor,andthestresslevelsinthesprings.Resultsfromananalysisoftheelectro-mechanicalsensorshowninFigure2willbeusedas

Figure3.Electro-mechanicalsensordeflectedshape.

anexampleforthispaper.ThedeflectedshapeofthissensorisshowninFigure3forfullballtravel.Lookingatthedeflectedshapeofthespringscanprovideinsightintotheperformanceofthesensoraswellasaidinthedesignofthesensorhousing.Stressesinthespringsareimportantresultsinthisanalysistoensurestresslevelsinthespringsareatacceptablelevels.Desiredcomponentsofstresscanbeexaminedthroughvariousmeansincludingcolorcontourplots.Oneofthemostimportantresultsfromtheanalysisistheforce-displacementresponseforthesensorshowninFigure4.Fromthisforce-displacementresponse,theforcerequiredtopushspring1intocontactwithspring2canreadilybedetermined.Thisforcerequirementcanbeusedwithagivenaccelerationtodeterminethemassrequiredfortheball.Basedontheseresults,oneormorevariationsofseveralvariablessuchasspringwidth,springthickness,balldiameter,andballmaterialcanbeupdateduntiltheforce-displacementrequirementsareachievedwithinadesiredaccuracy.

AprototypeofthesensorshowninFigure2wasconstructedandtestedtodetermineitsactualforce-displacementresponse.Figure4showstheMSC/ABAQUSresultsalongwiththeexperimentalresultsfortheforce-displac