汽车参考资料安全气囊碰撞有限元分析外文翻译.docx
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汽车参考资料安全气囊碰撞有限元分析外文翻译.docx
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汽车参考资料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-dis
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