Riveted Lap Joints in Aircraft Fuselage: Design, Analysis and Properties

345 Pages·2012·9.3 MB·English

by  Andrzej Skorupa

Riveted Lap Joints in Aircraft Fuselage
SOLID MECHANICS ANDITS APPLICATIONS
Volume189
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Andrzej Skorupa • Małgorzata Skorupa
Riveted Lap Joints in Aircraft
Fuselage
Design, Analysis and Properties
123
AndrzejSkorupa MałgorzataSkorupa
FacultyofMechanicalEngineering FacultyofMechanicalEngineering
andRobotics andRobotics
AGHUniversityofScienceandTechnology AGHUniversityofScienceandTechnology
Al.Mickiewicza30 Al.Mickiewicza30
30-059Krako´w 30-059Krako´w
Poland Poland
ISSN0925-0042
ISBN978-94-007-4281-9 ISBN978-94-007-4282-6(eBook)
DOI10.1007/978-94-007-4282-6
SpringerDordrechtHeidelbergNewYorkLondon
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Preface
Fatigue of the pressurized fuselages of transport aircraft is a significant problem
for all builders and users of hundreds of thousands of aircraft, servicing millions
of air travellers and cargoes. Primary facets of this issue are: How to assure a
sufficient lifetime for each and every componentof each and every aircraft. How
todetermineadequatesafetyfeaturescompatiblewithdifferingstructures.Howto
formulate and enforce inspection procedures commensurate with the demands of
individualaircraft. These aspects are all addressedin variousformalprotocolsfor
creatingandmaintainingairworthiness,includingdamagetoleranceconsiderations.
In most transport aircraft, fatigue occurs in joints, and more especially in lap
jointsbetweensheetsofaluminiumalloys,sometimesleadingtocircumstancesthat
threaten safety in critical ways. This fact was recognized as early as the 1950s.
Since then, fatigue of lap joints has become a fundamental design question and
an increasingly detailed inspection problem for the aircraft operator. The aircraft
industry and the airlines are both interested in the use of thin sheet material in
ordertoachieveweightreduction.Moreover,theeconomicsofaircraftproduction,
theincreasingsophisticationofinspectionproceduresandtheneedforlengthened
lifetimes of aircraft already in service must all be considered. The problem of
fatigueoflapjointshasbeenconsiderablyenlargedbythegoalofextendingaircraft
lifetimeswhichmayalreadyexceed,e.g.,20years.
Fatigue of riveted lap joints between aluminium alloy sheets, typical of the
pressurizedaircraftfuselage,isthemajortopicofthisbook.Bondedlapjointsare
not included. These joints appear to have attractive fatigue properties. However,
no major breakthrough has occurred due to questions associated with production
techniques, quality assurance and inspections. One newcomer to the industry is
usingweldablealuminiumalloysinintegralstructureswithstiffeners,whichoffera
meansofreplacinglapjointsbybuttjoints.Longtimeserviceexperiencewiththese
structuresisnotyetavailableandthistypeofconnectionisalsooutsidethepresent
survey.
Fatigue response of a riveted connection depends on the integrated effect of
a large number of variables related to joint design and production and applied
loading conditions. In view of that dependency, numerous research programs on
v
vi Preface
fatigue of riveted lap joints have been carried out and reported in the literature,
as discussed in this book. The book consists of ten chapters. Chapter 1 gives
basicinformationonstructuraldesignsolutionsforfuselageskinjointsandloading
conditions.Althoughthe stress distributionin a fuselage lap jointis of a complex
character, a great majority of experimental studies reported in the literature were
carried out in laboratory conditions on simple small lap joint specimens under
uniaxial tension. The relevance of such results to riveted joints in a real structure
is considered in Chap. 2. The fatigue behaviour of riveted lap joints shows a
considerable dependency on factors associated with the production process. In
Chap.3,the followingproductionvariablesaretakenintoaccount:sheetmaterial,
rivet type and material as well as the manufacturing process, including riveting
techniques,rivetholeimperfections,surfacetreatmentofthesheetsandthesqueeze
force. The latter is a major factor that influences the fatigue behaviour of riveted
joints. In Chap. 4, the dependenceof joint fatigue performanceon various design
parametersisaddressed.Specifically,theeffectsofthenumberofrivetrows,rivet
row spacing, rivet pitch in a row, rivet pattern and sheet thickness are accounted
for. An analytical solution and experimental results on load transmission in lap
joints with mechanical fasteners are considered in Chap. 5. Special attention is
paid to the experimental and theoretical determination of fastener flexibility and
to frictionbetween the fayingsheetsin view of theirimportanceforload transfer.
Eccentricitiesoccurringintheoverlapregionofajointinduceaso-calledsecondary
bending. Estimates of secondary bending by means of simple analytical models,
FE computations and measurements are presented in Chap. 6. Also, implications
ofsecondarybendingforjointfatigueperformanceareconsidered.Thenucleation
and shape development of fatigue cracks in longitudinal lap joints is covered in
Chap. 7. Issues given special attention are the influence of the squeeze force on
the mode of failure and the significance of fretting for fatigue crack initiation.
Acharacteristicandverydangerousformoffatiguedamageinlongitudinalriveted
lapjointsistheso-calledmulti-sitedamage(MSD).InChap.8,passengeraircraft
catastrophic accidents due to MSD are described first. Next, an overview of
experimentalinvestigationsintoMSDperformedonfullscalefuselagepanelsand
rivetedlapjointspecimensisoffered.Chapter9isdevotedtofatiguecrackgrowth
and fatigue life prediction methodologyfor riveted lap joints, including the MSD
problem.Modelsandcodesmostcommonlyusedforthatpurposeareoutlinedand
stress intensity factor solutionsappropriatefor cracksat rivetholes are presented.
Aparticularconsiderationisgiventotheequivalentinitialflawsizeconceptdueto
its significancefor the predictionquality.Residualstrengthpredictionsforriveted
lap joints in a fuselage structure are addressed in Chap. 10. Failure criteria and
crackgrowthdirectionalcriteriaarethoroughlyconsidered.Variouscomputational
approaches to estimate residual strength of panels with riveted connections are
presented and reportedcomparisonsbetween predictionsand experimentalresults
arereviewed.Structuralriskanalysismethodologyapplicabletorivetedjointswith
MSD isoverviewed.Themajorissues ofeachchapterarerecapitulatedin thelast
section.Thematerialpresentedinthebookisrichlyillustrated.
Acknowledgements
Thoughthe authorsof the bookappear to be the only contributorsto its contents,
in reality it is an achievement made possible due to the help and efforts of other
personswhomwewouldliketothank.
FirstofallwewanttoexpressourdeepestthankstoProf.JaapSchijvefromthe
DelftUniversityofTechnology,ourfriendandcollaboratorformanyyears,forhis
encouragement, enduring help and interest in this work. Without his suggestions
andsupport,inparticularprovidinguswithanumberofliteraturesourcestowhich
itwasdifficulttogainaccess,wewouldhaveneverbeenabletopreparethisbook.
We want to express our appreciation to Johannes Homan, M.Sc., from Fatec
Engineeringforhisusefulcommentsandinformationonsomeselectedproblems.
Our co-workers Dr. Tomasz Machniewicz and Adam Korbel, M.Sc., from the
AGH University of Science and Technologyin Krako´wwere always available for
discussion.Theyalsodeserveourparticularthanksfortheirgreathelpinpreparing
thefiguresinaprintableform.
We gratefullyacknowledgethethoroughworkdonebyMr.EdwinBeschler,an
EnglishlanguagecopyeditorprovidedbySpringertoimprovethetextofthebook.
With respect to publishing the book by Springer, we appreciate the nice and
effective cooperation with Ms. Nathalie Jacobs and Ms. Anneke Pot as well as
Ms.ArulmuruganPavitraresponsibleforthetypesettingofthebook.
An incentive to write this book was the authors’ participation in projects con-
cerningfatigueofrivetedjointsinaircraftstructures.Financialsupportfromtheas-
sociatedgovernmentalresearchfundswithintheyears2009–2012isacknowledged.
vii

Contents
Nomenclature..................................................................... xiii
UnitsandConversionFactors .................................................. xv
1 RivetedLapJointsinaPressurizedAircraftFuselage................. 1
1.1 ConstructionalSolutionsoftheFuselageSkinStructure........... 1
1.2 LoadingConditionsforaLongitudinalLapSpliceJoint........... 3
1.3 BondedandRiveted-BondedLapJoints............................ 7
1.4 FatigueDamageofLongitudinalLapSpliceJoints ................ 9
1.5 SummaryofThisChapter............................................ 9
2 Differences Between the Fatigue Behaviour
of Longitudinal Lap Joints in a Pressurized
FuselageandLaboratoryLapJointSpecimens......................... 11
2.1 StressDistributionandSpecimenGeometry........................ 11
2.2 EffectoftheLoadFrequencyandEnvironmentalConditions ..... 22
2.3 SummaryofThisChapter............................................ 25
3 ProductionVariablesInfluencingtheFatigueBehaviour
ofRivetedLapJoints....................................................... 27
3.1 SheetMaterial........................................................ 27
3.2 FastenerTypeandMaterial.......................................... 33
3.3 ManufacturingProcess............................................... 42
3.3.1 RivetingMethod............................................ 42
3.3.2 ImperfectionsofRivetHoles............................... 44
3.3.3 ColdWorkingofRivetHoles .............................. 48
3.3.4 SurfaceTreatmentoftheSheets ........................... 50
3.3.5 SqueezeForce .............................................. 55
3.4 SummaryofThisChapter............................................ 99
4 DesignParametersInfluencing theFatigueBehaviour
ofRivetedLapJoints....................................................... 101
4.1 NumberofRivetRows............................................... 101
ix
x Contents
4.2 RivetRowSpacing................................................... 104
4.3 RivetPitchinRow ................................................... 108
4.4 DistanceoftheRivetfromtheSheetEdge.......................... 109
4.5 RivetPattern.......................................................... 110
4.6 SheetThickness ...................................................... 111
4.7 SizeEffect............................................................ 113
4.8 SummaryofThisChapter............................................ 114
5 LoadTransferinLapJointswithMechanicalFasteners .............. 115
5.1 SimpleComputationofAxialForcesintheSheets................. 115
5.2 FastenerFlexibility................................................... 120
5.2.1 AnalyticalSolution......................................... 120
5.2.2 ExperimentalDetermination............................... 122
5.3 MeasurementResultsonLoadTransmission....................... 130
5.4 FrictionalForces...................................................... 134
5.5 SummaryofThisChapter............................................ 143
6 SecondaryBending forMechanicallyFastenedJoints
withEccentricities.......................................................... 145
6.1 ThePhenomenonofSecondaryBending ........................... 145
6.2 AnalyticalInvestigations............................................. 146
6.2.1 Models ...................................................... 146
6.2.2 ExemplaryApplicationstoLapJoints..................... 151
6.3 FiniteElementModelling............................................ 158
6.4 MeasurementsofSecondaryBending............................... 162
6.4.1 Methodology................................................ 162
6.4.2 Comparisons Between Measured
andComputedResults...................................... 165
6.4.3 ParametricStudies.......................................... 169
6.4.4 InSituMeasurementResults............................... 172
6.5 FatigueBehaviourofJointsExhibitingSecondaryBending....... 175
6.5.1 EffectofSecondaryBendingonFatigueLife............. 175
6.5.2 EffectofFayingSurfaceConditions....................... 181
6.6 SummaryofThisChapter............................................ 183
7 CrackInitiationLocationandCrackShapeDevelopment
inRivetedLapJoints–ExperimentalTrends........................... 185
7.1 CrackInitiationSite.................................................. 185
7.1.1 StaticLoading .............................................. 185
7.1.2 FatigueLoading ............................................ 188
7.2 TheRoleofFretting.................................................. 194
7.2.1 ThePhenomenonofFretting............................... 194
7.2.2 CrackinginthePresenceofFretting....................... 197
7.3 FatigueCrackShapeDevelopment.................................. 199
7.4 SummaryofThisChapter............................................ 206