Polymer composites in the aerospace industry

515 Pages·2014·37.21 MB·English

by  E Irving

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Woodhead Publishing Series in Composites
Science and Engineering: Number 50
Polymer Composites in
the Aerospace Industry
Edited by
P. E. Irving and C. Soutis
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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).