Related titles Residualstressesincompositematerials (ISBN978-0-85709-270-0) Failuremechanismsinpolymermatrixcomposites (ISBN978-1-84569-750-1) Manufacturingtechniquesforpolymermatrixcomposites (ISBN978-0-85709-067-6) Woodhead Publishing Series in Composites Science and Engineering: Number 50 Polymer Composites in the Aerospace Industry Edited by P. E. Irving and C. Soutis AMSTERDAM(cid:129)BOSTON(cid:129)CAMBRIDGE(cid:129)HEIDELBERG LONDON(cid:129)NEWYORK(cid:129)OXFORD(cid:129)PARIS(cid:129)SANDIEGO SANFRANCISCO(cid:129)SINGAPORE(cid:129)SYDNEY(cid:129)TOKYO WoodheadPublishingisanimprintofElsevier WoodheadPublishingisanimprintofElsevier 80HighStreet,Sawston,Cambridge,CB223HJ,UK 225WymanStreet,Waltham,MA02451,USA LangfordLane,Kidlington,OX51GB,UK Copyright©2015ElsevierLtd.Allrightsreserved. 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BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary LibraryofCongressControlNumber:2014944430 ISBN978-0-85709-523-7(print) ISBN978-0-85709-918-1(online) ForinformationonallWoodheadPublishingpublications visitourwebsiteathttp://store.elsevier.com/ TypesetbyTNQBooksandJournals www.tnq.co.in PrintedandboundintheUnitedKingdom List of contributors E. Archer University of Ulster, Newtownabbey,UK R.H.Bossi The Boeing Company, Seattle,WA, USA A.J. Brunner Empa,D€ubendorf,Switzerland R. Butler University ofBath, Bath, UK W.J. Cantwell Khalifa University of Science, Abu Dhabi,United Arab Emirates M. David German Aerospace Center (DLR), Stuttgart,Germany G. Davies Imperial College, London, UK J.P.Foreman University ofSheffield,Sheffield,UK V. Giurgiutiu University ofSouthCarolina, Columbia, SC, USA P.Irving Cranfield University, Cranfield,UK D.S. Ivanov University ofBristol, Bristol, UK A.F. Johnson Composites Consultant, Stuttgart, Germany F.R. Jones University of Sheffield,Sheffield,UK M.W. Joosten RMIT University, Melbourne, VIC, Australia C. Kassapoglou Delft University ofTechnology,Delft, The Netherlands G.S. Langdon University of Cape Town, Rondebosch, SouthAfrica S.V. Lomov KU Leuven, Leuven, Belgium C.T. McCarthy University ofLimerick,Limerick, Ireland M.A. McCarthy University of Limerick,Limerick,Ireland A. McIlhagger University of Ulster,Newtownabbey, UK R. McIlhagger University of Ulster,Newtownabbey, UK M. Quaresimin University of Padova, Padova, Italy C. Soutis The University of Manchester, Manchester,UK R. Talreja TexasA&MUniversity, College Station, TX, USA R.S. Thomson Advanced Composite Structures Australia, Port Melbourne, VIC, Australia Woodhead Publishing Series in Composites Science and Engineering 1 Thermoplasticaromaticpolymercomposites F.N.Cogswell 2 Designandmanufactureofcompositestructures G.C.Eckold 3 Handbookofpolymercompositesforengineers EditedbyL.C.Hollaway 4 Optimisationofcompositestructuresdesign A.Miravete 5 Short-fibrepolymercomposites EditedbyS.K.DeandJ.R.White 6 Flow-inducedalignmentincompositematerials EditedbyT.D.PapthanasiouandD.C.Guell 7 Thermosetresinsforcomposites CompiledbyTechnolex 8 Microstructuralcharacterisationoffibre-reinforcedcomposites EditedbyJ.Summerscales 9 Compositematerials F.L.MatthewsandR.D.Rawlings 10 3-Dtextilereinforcementsincompositematerials EditedbyA.Miravete 11 Pultrusionforengineers EditedbyT.Starr 12 Impactbehaviouroffibre-reinforcedcompositematerialsandstructures EditedbyS.R.ReidandG.Zhou 13 Finiteelementmodellingofcompositematerialsandstructures F.L.Matthews,G.A.O.Davies,D.HitchingsandC.Soutis 14 Mechanicaltestingofadvancedfibrecomposites EditedbyG.M.Hodgkinson 15 Integrateddesignandmanufactureusingfibre-reinforcedpolymericcomposites EditedbyM.J.OwenandI.A.Jones 16 Fatigueincomposites EditedbyB.Harris 17 Greencomposites EditedbyC.Baillie 18 Multi-scalemodellingofcompositematerialsystems EditedbyC.SoutisandP.W.R.Beaumont xiv WoodheadPublishingSeriesinCompositesScienceandEngineering 19 Lightweightballisticcomposites EditedbyA.Bhatnagar 20 Polymernanocomposites Y-W.MaiandZ-Z.Yu 21 Propertiesandperformanceofnatural-fibrecomposite EditedbyK.Pickering 22 Ageingofcomposites EditedbyR.Martin 23 Tribologyofnaturalfiberpolymercomposites N.ChandandM.Fahim 24 Wood-polymercomposites EditedbyK.O.NiskaandM.Sain 25 Delaminationbehaviourofcomposites EditedbyS.Sridharan 26 Scienceandengineeringofshortfibrereinforcedpolymercomposites S-Y.Fu,B.LaukeandY-M.Mai 27 Failureanalysisandfractographyofpolymercomposites E.S.Greenhalgh 28 Management,recyclingandreuseofwastecomposites EditedbyV.Goodship 29 Materials,designandmanufacturingforlightweightvehicles EditedbyP.K.Mallick 30 Fatiguelifepredictionofcompositesandcompositestructures EditedbyA.P.Vassilopoulos 31 Physicalpropertiesandapplicationsofpolymernanocomposites EditedbyS.C.TjongandY-W.Mai 32 Creepandfatigueinpolymermatrixcomposites EditedbyR.M.Guedes 33 Interfaceengineeringofnaturalfibrecompositesformaximumperformance EditedbyN.E.Zafeiropoulos 34 Polymer-carbonnanotubecomposites EditedbyT.McNallyandP.P€otschke 35 Non-crimpfabriccomposites:Manufacturing,propertiesandapplications EditedbyS.V.Lomov 36 Compositereinforcementsforoptimumperformance EditedbyP.Boisse 37 Polymermatrixcompositesandtechnology R.Wang,S.ZengandY.Zeng 38 Compositejointsandconnections EditedbyP.CamanhoandL.Tong 39 Machiningtechnologyforcompositematerials EditedbyH.Hocheng 40 Failuremechanismsinpolymermatrixcomposites EditedbyP.Robinson,E.S.GreenhalghandS.Pinho 41 Advancesinpolymernanocomposites:Typesandapplications EditedbyF.Gao 42 Manufacturingtechniquesforpolymermatrixcomposites(PMCs) EditedbyS.AdvaniandK-T.Hsiao WoodheadPublishingSeriesinCompositesScienceandEngineering xv 43 Non-destructive evaluation (NDE) of polymer matrix composites: Techniques and applications EditedbyV.M.Karbhari 44 Environmentallyfriendlypolymernanocomposites:Types,processingandproperties S.S.Ray 45 Advancesinceramicmatrixcomposites EditedbyI.M.Low 46 Ceramicnanocomposites EditedbyR.BanerjeeandI.Manna 47 Naturalfibrecomposites:Materials,processesandproperties EditedbyA.HodzicandR.Shanks 48 Residualstressesincompositematerials EditedbyM.Shokrieh 49 Health and environmental safety of nanomaterials: Polymer nanocomposites and othermaterialscontainingnanoparticles EditedbyJ.Njuguna,K.PielichowskiandH.Zhu 50 Polymercompositesintheaerospaceindustry EditedbyP.E.IrvingandC.Soutis 51 Biofiberreinforcementincompositematerials EditedbyO.FarukandM.Sain 52 Fatigue andfractureof adhesively-bondedcompositejoints: Behaviour,simulation andmodelling EditedbyA.P.Vassilopoulos 1 Introduction: engineering requirements for aerospace composite materials C. Soutis The University of Manchester, Manchester, UK 1.1 Introduction Compositematerialshavegainedpopularity(despitetheirgenerallyhighcost)inhigh performanceproductsthatneedtobelightweight,yetstrongenoughtotakehighloads such as aerospace structures (tails, wings and fuselages), boat construction, bicycle framesandracingcarbodies.Otherusesincludestoragetanksandfishingrods.Nat- ural composites (wood and fabrics) have found applications in aircraft from the first flight of the Wright Brothers’ Flyer 1, in North Carolina on December 17, 1903, to the plethora of uses now enjoyed by man-made (engineered) composite materials on both military and civil aircraft, in addition to more exotic applications on unmanned aerial vehicles (UAVs), space launchers and satellites. Their adoption as a major contribution to aircraft structures followed on from the discovery of carbon fibre at the Royal Aircraft Establishment at Farnborough, UK, in 1964. However, not until thelate1960sdidthesenewcompositesstarttobeapplied,onademonstrationbasis, tomilitary aircraft. Examples ofsuchdemonstratorsweretrim tabs,spoilers, rudders and doors. With increasing application and experience of their use came improved fibresandmatrixmaterials(thermosetsandthermoplastics)resultinginCFRPcompos- iteswithimprovedmechanicalproperties,allowingthemtodisplacethemoreconven- tional materials, aluminium and titanium alloys, for primary structures. In the followingsections,thepropertiesandstructureofcarbonfibresarediscussedtogether withthermoplasticandthermosetresinsandthesignificanceoftheinterfacebetween the fibre andthe matrix (resin). 1.1.1 Carbon fibre types and properties Highstrength,highmoduluscarbonfibresareabout5e6mmindiameterandconsistof small crystallites of ‘turbostratic’ graphite, one of the allotropic forms of carbon. The graphite structure consists of hexagonal layers, in which the bonding is covalent and strong(w>525kJ/mol)andthereareweakvanderWaalforces(<10kJ/mol)between the layers [1,2]. This means that the basic crystal units are highly anisotropic; the in- plane Young’s modulus parallel to the a-axis is approximately 1000GPa and the Young’smodulusparalleltothec-axisnormaltothebasalplanesisonly30GPa.Align- mentofthebasalplaneparalleltothefibreaxisgivesstifffibres,which,becauseofthe PolymerCompositesintheAerospaceIndustry.http://dx.doi.org/10.1016/B978-0-85709-523-7.00001-3 Copyright©2015ElsevierLtd.Allrightsreserved. 2 PolymerCompositesintheAerospaceIndustry relativelowdensityofaround2Mg/m3,haveextremelyhighvaluesofspecificstiffness (w200GPa/(Mg/m3)).Imperfectionsinalignmentintroducedduringthemanufacturing processresultincomplex-shapedvoidselongatedparalleltothefibreaxis.Theseactas stressraisersandpointsofweaknessleadingtoareductioninstrengthproperties.Other sourcesofweakness,whichareoftenassociatedwiththemanufacturingmethod,include surface pits and macro-crystallites. The arrangement of the layer planes in the cross- sectionofthefibreisalsoimportantsinceitaffectsthetransverseandshearproperties ofthefibre.Thus,forexample,thenormalpolyacrylonitrile-based(PAN-based)TypeI carbon fibres have a thin skin of circumferential layer planes and a core with random crystallites.Incontrast,somemesophasepith-basedfibresexhibitradiallyorientedlayer structures.Thesedifferentstructuresresultinsomesignificantdifferencesintheproper- tiesofthefibresandofcoursethoseofthecomposites. Refinementsinfibreprocesstechnologyoverthepast20yearshaveledtoconsider- ableimprovementsintensilestrength(w4.5GPa)andinstraintofracture(more than 2%) for PAN-based fibres. These can now be supplied in three basic forms, high modulus(HM,w380GPa),intermediatemodulus(IM,w290GPa)andhighstrength (HS, with a modulus of around 230GPa and tensile strength of 4.5GPa). The more recentdevelopmentsofthehighstrengthfibreshaveledtowhatareknownashighstrain fibres,whichhavestrainvaluesof2%beforefracture.Thetensilestressestrainresponse iselasticuptofailure,andalargeamountofenergyisreleasedwhenthefibresbreakina brittlemanner.Theselectionoftheappropriatefibredependsverymuchontheapplica- tion. For militaryaircraft, bothhighmodulus and high strengthare desirable. Satellite applications, in contrast, benefit from use of high fibre modulus improving stability andstiffnessforreflectordishes,antennasandtheirsupportingstructures. Rovingsarethebasicformsinwhichfibresaresupplied,arovingbeinganumberof strandsorbundlesoffilamentswoundintoapackageorcreel,thelengthoftherovingbe- ing up to several kilometres, depending on the package size. Rovings or tows can be woven into fabrics, and a range of fabric constructions are available commercially, suchasplainweave,twillsandvarioussatinweavestyles,wovenwithachoiceofroving ortowsizedependingontheweightorarealdensityoffabricrequired.Fabricscanbe woven with different kinds of fibre, for example, carbon in the weft and glass in the warpdirection,andthisincreasestherangeofpropertiesavailabletothedesigner.One advantageoffabricsforreinforcingpurposesistheirabilitytodrapeorconformtocurved surfaceswithoutwrinkling.Itisnowpossible,withcertaintypesofknittingmachine,to produce fibre performs tailored to the shape of the eventual component. Generally speaking,however,themorehighlyconvolutedeachfilamentbecomes,asatcrossover pointsinwovenfabrics,orasloopsinknittedfabrics,theloweritsreinforcingability. 1.1.2 Fibre-matrix interface Thefibresaresurfacetreatedduringmanufacturetoprepareadhesionwiththepolymer matrix, whether thermosetting (epoxy, polyester, phenolic and polyimide resins) or thermoplastic(polypropylene,Nylon6.6,PMMA,PEEK).Thefibresurfaceisrough- ened by chemical etching and then coated with an appropriate size to aidbonding to thespecifiedmatrix.Whereascompositetensilestrengthisprimarilyafunctionoffibre Introduction:engineeringrequirementsforaerospacecompositematerials 3 properties, the ability of the matrix to both support the fibres (required for good compressionstrength)andprovideout-of-planestrengthis,inmanysituations,equally important.Theaimofthematerialsupplieristoprovideasystemwithabalancedsetof properties. While improvements in fibre and matrix properties can lead to improved lamina or laminate properties, the all-important field of fibre-matrix interface must not beneglected. The load acting on the matrix has to be transferred to the reinforcement via the interface. Thus, fibres must be strongly bonded to the matrix if their high strength andstiffnessaretobeimpartedtothecomposite.Thefracturebehaviourisalsodepen- dent on the strength of the interface. A weak interface results in a low stiffness and strengthbuthighresistancetofracture,whereasastronginterfaceproduceshighstiff- nessandstrengthbutoftenalowresistancetofracture,i.e.,brittlebehaviour.Conflict therefore exists and the designer must select the material most nearly meeting his requirements. Other properties of a composite, such as resistance to creep, fatigue andenvironmentaldegradation,arealsoaffectedbythecharacteristicsoftheinterface. In these cases the relationship between properties and interface characteristics are generally complex, and analytical/numerical models supported by extensive experi- mentalevidence arerequired. 1.1.3 Resin materials Thermoplastic materials are becoming more available, however, the more conven- tionalmatrix materials currently usedarethermosetting epoxies.The matrix material istheAchillesheelofthecompositesystemandlimitsthefibrefromexhibitingitsfull potentialinterms oflaminateproperties.Thematrixperforms anumberoffunctions amongst which are stabilising the fibre in compression (providing lateral support), translating the fibre properties into the laminate, minimising damage due to impact by exhibiting plastic deformation and providing out-of-plane properties to the lami- nate. Matrix-dominated properties (interlaminar strength, compressive strength) are reduced when the glass transition temperature is exceeded, and whereas with a dry laminate this is close to the cure temperature, the inevitable moisture absorption re- duces this temperature and hence limits the application of most high-temperature- (cid:1) cure thermoset epoxycompositesto less than 120 C. Conventionalepoxyaerospaceresinsaredesignedtocureat120e135(cid:1)Cor180(cid:1)C usuallyinanautoclaveorclosedcavitytoolatpressuresupto8bar,occasionallywitha post cure at higher temperature. Systems intended for high temperature applications (cid:1) maybeundergocuringattemperaturesupto350 C.Theresinsmusthavearoomtem- peraturelifebeyondthetimeittakestolayupapartandhavetime/temperature/viscosity suitableforhandling.Theresultantresincharacteristicsarenormallyacompromisebe- tweencertaindesirablecharacteristics.Forexample,improveddamagetoleranceperfor- mance usually causes a reduction in hot-wet compression properties, and if this is attained by an increased thermoplastic content, then the resin viscosity can increase significantly.Increasedviscosityisespeciallynotdesiredforaresintransfermoulding (RTM)resinwhereaviscosityof50cPsorlessisoftenrequired,buttoughnessmayalso beimpartedbythefabricstructuresuchasastitchednon-crimpedfabric(NCF).