R. Compression Response of a Sandwich Fuselage Kee

NASATechnicalMemorandum110302CompressionResponseofaSandwichFuselageKeelPanelWithandWithoutDamageDavidM.McGowanandDamodarR.AmburLangleyResearchCenter,Hampton,VirginiaFebruary1997NationalAeronauticsandSpaceAdministrationLangleyResearchCenterHampton,Virginia23681-00011COMPRESSIONRESPONSEOFASANDWICHFUSELAGEKEELPANELWITHANDWITHOUTDAMAGEDavidM.McGowanandDamodarR.AmburNASALangleyResearchCenterHampton,VAABSTRACTResultsarepresentedfromanexperimentalandanalyticalstudyofasandwichfuselagekeelpanelwithandwithoutdamage.Thefuselagekeelpanelisconstructedofgraphite-epoxyskinsbondedtoahoneycombcore,andisrepresentativeofahighlyloadedfuselagekeelstructure.Thefacesheetsofthepanelcontainseveralterminatedordroppedpliesalongthelengthofthepanel.Theresultspresentedprovideabetterunderstandingoftheloaddistributionindamagedandundamagedthick-face-sheetcompositesandwichstructurewithdroppedpliesandofthefailuremechanismsofsuchstructureinthepresenceoflow-speedimpactdamageanddiscrete-sourcedamage.Theimpact-damageconditionstudiedcorrespondstobarelyvisibleimpactdamage(BVID),andthediscrete-sourcedamageconditionstudiedisanotchmachinedthroughbothfacesheets.Resultsarepresentedfromanimpact-damagescreeningstudyconductedonanotherpanelofthesamedesigntodeterminetheimpactenergynecessarytoinflictBVIDonthepanel.Resultsarepresentedfromcompressiontestsofthepanelinthreeconditions:undamaged;BVIDintwolocations;andBVIDintwolocationsandanotchthroughbothfacesheets.Surfacestrainsinthefacesheetsoftheundamagedpanelandthenotchedpanelobtainedexperimentallyarecomparedwithfiniteelementanalysisresults.Theexperimentalandanalyticalresultssuggestthatforthedamageconditionsstudied,discrete-sourcedamageinfluencesthestructuralperformancemorethanBVID.INTRODUCTIONOneoftheprimarygoalsoftheAdvancedCompositesTechnology(ACT)programistodeveloptheenablingtechnologythatwillallowcompositematerialstobeusedintheprimarywingandfuselagestructuresofthenextgenerationadvancedsubsonictransportaircraft.UndertheACTprogram,theBoeingCommercialAircraftGroup(BCAG)hasbeenworkingtodevelopcost-effectiveandstructurallyefficientcompositefuselagestructure.1Thefocusofthisworkhasbeenonthefuselagesectionjustaftofthemainlandinggearwheelwellofamodernwide-bodytransportwhichisdesignatedasSection46onaBoeing2aircraft.Thisfuselagesectionis33feetlongand20feetindiameter,andcontainscrown,sideandkeelquadrantsections(seeFig.1).2AsshowninFig.1,thecurrentfuselagedesignconceptutilizesskin-stringerconstructioninthecrownquadrantsectionandsandwichconstructioninthesideandkeelquadrantsections.Sandwichstructureisbeingusedinthedesignofthesideandkeelquadrantsectionsbecauseithasthepotentialforhighstructuralefficiencyandlow-costmanufacturingandhasbeenusedextensivelyinstiffness-criticalaircraftsecondarystructures.Theapplicationofsandwichstructuresinaircrafthasbeenrestrictedinthepastduetoundesirablemoistureabsorptionandmoistureretentioncharacteristics,andduetoaninsufficientunderstandingoflow-speedimpact-damagemechanismsandtheeffectofsuchdamage,aswellaspenetrationdamage,onthestructuralperformanceofsandwichstructures.Nowthatsandwichconceptsarebeingconsideredforapplicationtoaircraftprimarystructures,understandingtheeffectsoflow-speedimpactdamageandpenetrationdamageonsandwichstructureshasbecomeimportant.AjointNASA/Boeingstudyofthetechnologyissuesassociatedwithusingcomposite-face-sheetsandwichstructureinsubsonictransportfuselagesideandkeelpanelsisbeingconductedaspartoftheACTprogram.Thisstudyconsistsofmanufacturing,testingandanalyzingfull-scalekeel-andside-quadrant-sectionsandwichpanels.Thepresentpaperpresentstheresultsofanexperimentalandanalyticalstudyofthecompressionresponseofasandwichfuselagekeelpanelwithandwithoutdamage.ThetestpanelisrepresentativeofthestructurethatwouldbeusedinthekeelquadrantsectionofthehighlyloadedforwardendofSection46.Theobjectivesofthestudyaretounderstandtheloaddistributioninthethickcompositefacesheetsofthesandwichpanelwithandwithoutimpactdamage,andtodeterminepanelfailuremechanismsinthepresenceofbothimpactdamageandpenetratingdiscrete-sourcedamage.Theimpact-damageconditionsimulatedintheexperimentalstudycorrespondstobarelyvisibleimpactdamage(BVID).Theimpact-energylevelsnecessarytoinflictBVIDonthepanelaredeterminedthroughanimpact-damagescreeningtestthatwasperformedusinganotherpanelofthesamedesign.Thesimulateddiscrete-sourcedamagecorrespondstopenetrationdamagethroughbothfacesheets.Thepenetrationdamageissimulatedbyanotchmachinedthroughbothfacesheets.Theanalyticalstudyconsistsoffiniteelementanalysesoftheundamagedpanelandthenotchedpanel.Testresultsforsurfacestrainsarecomparedwithfiniteelementanalysisresultsfortheundamagedpanelandthenotchedpanel.Face-sheetsurfacestrainsthatillustrateloadredistributionaroundtheimpact-damageandnotchsitesarealsopresented.Finally,thepresentpaperdescribesthepanelfailurecharacteristicsinthepresenceofBVIDanddiscrete-sourcedamage.3TESTPANELDESCRIPTIONTheforwardkeelpaneltestarticleisrepresentativeofthestructurethatwouldbeusedinthekeelquadrantsectionofthehighlyloadedforwardendofSection46.Asdiscussedinre