Numerical simulation of soft-body impact on GFRP

Numericalsimulationofsoft-bodyimpactonGFRPlaminatecomposites:mixedSPH-FEandpureSPHapproachesRicardoL.AzevedoWestParanáStateUniversity,Cascavel/PR–BrazilMarcílioAlvesGroupofSolidMechanicsandStructuralImpact,DepartmentofMechatronicsandMechanicalSystemEngineering,UniversityofSãoPaulo,SãoPaulo/SP–BrazilAbstractImpacteventsinvolvinglaminatecompositeshadbeenlargelystudiedthroughcomputationalapproaches,duemainlytothetechnicaldifficultiesandhighcostsassociatedwithexperimentaltests,andtheavailabilityofhighlysophisticatedcomputationalcodes.Inthepresentwork,medium-to-highvelocitiesimpacteventsof‘dummybirds’againstbalancedS2-Glass/EpoxylaminatecompositesaresimulatedthroughLS-Dynaexplcitfiniteelementpackage.Pureandmixedformulationcouplingfiniteelements(FE)andsmoothedparticlehydrodynamics(SPH)techniquesisadoptedtodescribethemotionoftheimpactedcompositeplateandthesoftbodyprojectile,respectively.Theseveredistortionsandthedamageinducedontheplatebytheimpactimplytheremotionofsomeelementsofthemesh,inordertobecomepossiblethecontinuityofthesimulationwithoutadooptingveryreducedtimesteps.AnalternativeapproachconsistingofSPHformulationofbothprojectileandtargetplateisadoptedandcomparisonsbetweenthethesenumericalproceduresaremade.Keywords:impact,laminatecomposites,FiniteElementMethod,SmoothedParticleHydrodynamics,LS-Dyna.1IntroductionTheimpactofbirdswithaircraftstructuresisoneofthemainthreatsforflightsafety.Duetheconsiderablepresenceofbirdsinthevicinityofairportsalargenumberofthesebirdstrikesoccuraroundtheworld.Inthelasttwodecadesasignificantexpansionoftheuseoffiberreinforcedcompositematerialsinaeronauticalindustryhasbeenverified,aimingtoobtainstructureswithadvantageousstrength/weightratios.However,thedamageinducedbyimpactincompositematerialsisanaspectthatinhibitstheapplicationofthiskindofmaterial,sinceitiswellknownthatcompositesareveryMechanicsofSolidsinBrazil2009,H.S.daCostaMattos&MarcílioAlves(Editors)BrazilianSocietyofMechanicalSciencesandEngineering,ISBN978-85-85769-43-716R.L.AzevedoandM.Alvessusceptibletotransverseimpact.Inthebird-aircraftimpactthebirdischaracterizedasasoftbody,i.e.bodywithlowrigidity/hardness,becausethestressesgeneratedarebeyondthestrengthofthebirdandgenerallybelowthestrengthofthetarget.Moreover,thebirdbehaveslikeafluidintheimpactevent,andtheeffectarelargeareaofthetarget[1].Thus,theprobleminconsiderationjoinssomeverycomplexaspects,suchashighstrainrates,largedeformations,complexconstitutiverelationshipsanddamage/failuremechanisms,amongothers.Therefore,thiscomplexityusuallyprecludestheuseofanalyticalsolutionstosolvethisclassofproblems.Consideringthatexperimentaltestsatebothexpensiveandtroublesome,computationalmethodshavebeenextensivelybytheaircraftindustrytominimizethenumberofexperiments,aimingthiswaytoreducecertificationanddevelopmentcostsandsupportthedesignofefficientbird-proofstructures.Inthissense,nonlinearexplicitcodesbasedonFiniteElement(FE)techniqueshavebeensuccessfullyemployedtoalargenumberofprobleminthefieldofContinuumMechanicssincelateeighties.TheLS-Dynacode[2]isageneralpurposefiniteelementcodefornon-linearstructuraldynamics,whichhasbeenlargelyemployedtoimpactanalysis[3–6].Impactofbodieswithlowrigidityandhardness,asthoseconsideredinthebirdimpactanalysis,hasbeentreatedintheaeronauticalindustryandresearchcentersthroughtheso-called‘substitutebirds’[7,8],materialswhosemechanicalbehaviorresemblesrealbirds,withadvantagesinwhatitreferstotheuniformityandrepeatabilityoftheexperimentaltests,usuallyconductedbyusinggasgunprojectilelaunchers.Recently,aimingtoovercomethedifficultiesofLagrangiandescriptiontohandlelargedistortionsofthemesh,ithasbeenproposedintheliteraturetheuseofSmoothedParticleHydrodynamics(SPH),ameshlessmethoddevelopedinitiallytosimulateastrophysicalproblemsandlaterextendedtoseveralotherapplicationsinComputationalMechanics.Examplesoftheuseofsuchtechnique,alreadyincorporatedtoLS-Dyna[9],canbefoundintheworksofAnghilerietal.[3]andRyabovetal.[5].ComparativestudiesofLagrangian,EulerianandSPHformulationshavebeenpresentedbySchewer[10]andBuyuketal.[11]inballisticimpactsimulation,byAnghilerietal.[3]influid-structureinteractionproblemsand,morerecently,byHuertas[12]analyzingbird-strikeeventsthroughLS-Dynaandthreedistinctformulations:Lagrangian,ArbitraryLagrangianEulerian(ALE)andSPH.Thepresentworkpresentsanumericalsimulationoftheimpactbetweenasubstitutebirdandaglassfiber-reinforcedpolymer(GFRP),morespecificallyaS2-Glass/Epoxycompositeplate,byusingtheLS-Dynacode.Duethelackoftestdatathematerialbehavioroftheidealizedbirdisapproximatedasthatofthewater,assuggestedintheliterature[4,8].Combinationsoftwodifferentapproachestodescribethemotionofthebirdareinvestigated,namelytheclassicalLagrangianFEandtheSPH.Theresultsobtained,aswellasthecomputationalperformanceofeachmethod,arecriticallycompared,andaqualitativecomparisonwithexperimentalresultsobtainedatGroupofSolidMechanicsandStructuralImpact(GMSIE/USP)isperformed.2ProblemdescriptionTheimpacthereconsideredisthatofacircularcylindricalsoftbody,theplasticine(‘play-doh’model-ingcompound)’bird’,whi