bonded boron/epoxy doublers for reinforcement of … bonded boron epoxy doublers for the...
TRANSCRIPT
BondedBoron/EpoxyDoublersforReinforcementof
MetallicAircraftStructures
PRESENTATIONOUTLINE
• BoronDoublerDescription– ReinforcementConcept– Advantages
• InstallationProcess– SurfacePreparation– MaterialsandBondingProcess– Inspection
• Applications– Military– Commercial
• TestPrograms
BoronEpoxyDoublers
Metal Structure
Applied Stress
Applied Stress Structural Damage
(Stop-Drilled Crack Shown)
Film Adhesive Boron Fiber Direction
Boron Doubler Reinforcement Concept Multi-ply Bonded Boron/Epoxy Doubler
ADVANTAGESOFBORON/EPOXYDOUBLERS
• BondedInstallation– NoAdditionalHolesinAircraft– NoFastener‐AssociatedStressRisers– OnlyOneSideAccessRequired– CanReinforceWhereRivetingisNotPossible
• HighSpeciQicModulus– EfQicientLoadTransfer– Thinner,Lighter
ADVANTAGESOFBORON/EPOXYDOUBLERS
• Non‐MetallicMaterial– Conformable– DoesNotCorrode– GalvanicallyInert
• UsedforDamageRepairandStructuralEnhancement
DoublerInstallationProcess
INSTALLATIONPROCESS
• Lay‐Up– DesignforSpeciQicLoadConQiguration– StandardLaminateConvention– CanBeAssembledAheadofTime– DoublersCanBePre‐curedforSpeciQicConQigurations
INSTALLATIONPROCESS
• AluminumSurfacePreparation MostCriticalStep
– PaintRemovalPerConventionalProcess– CleanandAbradeSurfaceSealUnderlyingFasteners– SurfaceTreatment
• PhosphoricAcidAnodizePACSProcess• Silane• Others
– ApplyandCurePrimer
INSTALLATIONPROCESS
• BondOntoAircraft– StructuralFilmAdhesive– PortableCureEquipment– VacuumBagPressure– DoublerCanBeCo‐cured
• Inspect– UltrasonicsforBond/CompositeQlaws– EddyCurrentforUnderlyingCrackGrowth
• Seal/Paint
Boron/Epoxy Doubler
Adhesive Primer
Aluminum Surface Treatment (e.g., Anodize)
Epoxy-Coat Rivet-Head
Load Load
Cover Ply
Aluminum Alloy Skin
Stop-Drilled Crack Underlying Rivet
Boron Doubler Installation Schematic
Applications
MILITARYAPPLICATIONS
MILITARYAPPLICATIONSUNDERDEVELOPMENT
Aircraft DoublerLocation
F‐15,F‐14 LowerWingSkinB‐1 HorizontalStabilizerSparC‐130 OuterWingStringersB‐52 UpperWingSkinF‐16 LowerwingFuelVentT‐38 LowerWingdoorFrameC‐5 NoseLandingGearDoorKC‐135 UpperWingSkin
COMMERCIALAPPLICATIONS
PerformanceTestPrograms
PERFORMANCETESTPROGRAM
• PerformedByBoeingTechnologyServices• Objectives:
– InstallationProcessSpeciQicationDevelopment– StructuralAnalysis‐BondedLineStresses– PerformanceTesting
• ValidationofStructuralEnhancement‐StaticTests• ValidationofCrackGrowthSuppression‐Fatigue
PROCESSSPECIFICATIONDEVELOPMENT
• SpeciQicationNumberD658‐10183‐1– DetailedDocumentationofMaterials,EquipmentandProcessingSteps
– OrientedTowardBoeingProcessSpeciQications– CriticalStepsValidatedThroughEmpiricalTesting
STRUCTURALANALYSIS
• INCAP‐LaminateAnalysisProgramUsedtoSizeDoublersforTesting
• COSMOS‐2DFEAUsedtoAnalyzeInternalStressesDuetoCureTemperatures
• NIKE‐3DFEAUsedtoEvaluateSpecimenGeometries
• ANSYS‐FEAUsedtoCharacterizeThermalandResidualStresses
STRUCTURALANALYSIS
• InformationGainedfromAnalysis– ShearandPeelStressesPeakatDoublerEdge– StressesinFrontofDoublerare25%HigherThanAppliedAxialStress
– ResidualStressesfromBondingOperations(thermal)OpposeAxialStressesDuringService‐ReducingPeakStressinDoubler
PERFORMANCETESTING‐STATICTESTS
• Objective:DetermineifDoublerRestoresUltimateAluminumStrength(78ksi,538MPa)toCrackedSpecimen
• TestsonBaselineSpecimensBeforeandAfterFatigueTesting
PERFORMANCETESTING‐STATICTESTRESULTS
• Pre‐Fatigue‐Quantity:12– AllSpecimens>78ksi(538MPa)Requirement– MostBrokeinAluminumOutsideDoubler
• Post‐Fatigue‐Quantity:91– 87Tests>78ksi(538MPa)– 4Tests42to76ksi(290to524MPa)
• AluminumFailurewithDoublerIntact
PERFORMANCETESTING
• Tension‐TensionFatigue– PrimaryObjectives:– DetermineifDoublerRestoresCyclicCapabilityofAircraftStructure
– BaselineSpecimensatRoomTemperature– ParametricStudiesRelatingtoDoublerDesign
• Sub‐Ambient(‐65oF,‐54oC)• GeometrySensitivities• Impact
FATIGUETARGETS
Design Design Test Test Aircraft Stress Cycles Stress Cycles
737 0 to 15 ksi 75,000 3 to 20 ksi 300,000 (0 to 103 MPa) (21 to 138 MPa)
747 0 to 18 ksi 20,000 3 to 20 ksi 300,000 (0 to 124 MPa) (21 to 138 MPa)
FATIGUERESULTS
• UnpatchedSpecimensFailat4000Cycles• Baseline:15Specimens
– 12Specimens‐NoFailure‐NoCrackGrowth– 1‐CrackGrowthat161,385cycles‐NoFailure– 1‐CrackGrowthat17,464cycles‐NoFailure– 1‐Failureat89,454– FailureandCrackGrowthaResultofImperfectionsinStopDrillHole
FATIGUERESULTS
• ObservationsFromParametricStudies– BaselinePerformanceMinimallyAffectedBy:
• VariationsinDoublerGeometries• ChangesinCurePressure• IncreasedCrackLength(1”,2.54cm)• MoistureandSolventImmersion• Impact@100and300Lb‐in• EdgeDisbonds0.5”in(1.27cm)Diameter
FATIGUETESTING
• ObservationsfromParametricStudies– CrackRe‐initiationMoreLikelytoOccur:
• WithIn‐LineRivetsNearCracks• DisbondsBeneathCrackedArea• ‐65DegreeF(53.8oC)Environment• NoStopDrillHole• TooThinaDoubler
– WhenCrackRe‐initiationOccurstheCrackGrowthisLinear(NotCatastrophic)
CONCLUSIONS
• BoronEpoxyDoublersHaveBeenSuccessfullyUsedonAircraftForManyYears
• ProcessHasBeenDeQinedandDocumented
• WhenProperlyDesignedandApplied,BoronEpoxyDoublersRestoreStructuralIntegrity