Repair of Composites Fact sheet - African Slum Journalaviationfacts.eu/.../Repair_of_Composites_Fact_sheet.pdf · Repair of Composites Fact sheet Introduction ... , the Airbus A350

REPAIROFCOMPOSITESINAEROSPACEINDUSTRY

REPAIR OF COMPOSITES FACT SHEET

RepairofCompositesFactsheet

IntroductionDecember152009,PaineField, EverettWashington.More than13,000employeesofBoeinggatheredaround towitness the first flightof theBoeing787DreamlinertoBoeingFieldinSeattle[1].Amilestoneinaviationindustry,becauseitwasaleaptowardsaircraftslargelybuildfromcompositematerials.Fouryearslater,onJune142013,theAirbusA350XWBtookoffforthefirsttimefromToulouse-BlagnacAirport.Boththe787Dreamliner’sandtheA350XWB’sstructuresaremainlyfromcompositematerial.Thebenefitsofcompositesarefairlyknown;astheAviationFactsfactsheetoncompositedamageinspection[2]states:“Compositesarelighter,strongerandhavemoredesignshapefreedomthanaluminium.Theseadvantagesarereasonswhyaircraftmanufacturersusemorecompositematerialsintheiraircraftnowadays.”However,theuseofcompositesalsohasitsdownsides,suchasintensivelabourindetectingdamageincompositematerialsandrepairingit[2]. OnJuly122014,aBoeing787DreamlinerfromEthiopianAircaughtfireatHeathrowAirport.Inordertobringtheaircraftbacktoservice,asectionofthefuselagehadtobereplaced,becauseoftheinabilitytorepairthedamagemadebythefire.Theaircraftwasbackinservicetwomonthslater.Aproblemwithcompositematerialsisthatthedamageontheoutsideisnotrepresentativefortheinnerstructure.Thiscancauseaproblemduringtherepairofcompositematerials.Butwhatdamagesoccurincompositematerials?Towhatextendcantheyberepaired?Andisthereawaytorepairalldamages?Thisfactsheetanswersthequestionsbyexplainingwhattypesofdamagesoccurinaviationcompositematerials,whattechniquesareusedforrepairingcompositematerialsandwhatdevelopmentsandaimsaretowardnewtechniques.

Figure1:FirstflightoftheB787,PainFieldinEverett,Washington,December15 Figure2:DamageduetofireontheBoeing787Dreamliner


Whatdamagesoccurincompositematerials?“All structures are designed for a purpose” [3]. This means that thedesignermustassurethatthestructurehasthecharacteristicstomeet itsgoalsintermsofstrength,elasticityandstiffness.Thesearethechallengesfor the designer, regardless of the material used. The designer finallychoosesamaterial thatmeetshisneeds.Because there is adifference incharacteristics between isotropic and anisotropic (composite) materials,thewaytheydeformorfailisalsodifferent.Also,compositematerialsarerecently introduced as the main material used for aircrafts. Whilecomposite applications in aerospace industry are increasing, there is littleaccuracyinfailurepredictionanddamageanalysis[3].Compositematerialsshow complex damage characteristics when loading [4]. Damages inaviation composite materials are caused by three cases: fatigue/cycleloading,impactonthematerialandmanufacturinginduceddefects.Fatigueisreferredtoasstatesofcyclicstress[3].Impactdamageisthecontactofadynamicobjectwiththematerial[5].Manufacturingerrorsaredefectsthatoccurs during the processing of composite materials, due to certaincombinationsofparameters. These typesofdamageswill firstoccuronamicroscopic level. Eventually themicroscopic defectswill accumulate andresult in damage on amacroscopic level,which has to be repaired. Thispartofthefactsheetstartsbygivinganoverviewofthedifferenttypesofdamage, on a microscopic level, with their characteristics, cause andpotentialdanger.InterfacialdebondingThe adhesion bond at the interfacial surface will affect the mechanical properties on amacroscopic level. Ithasan importantrole instresstransferbetweenfibreandmatrix.De-bonding(

Figure3) is causedwhen the interface isweakened,asa resultof fatigueloading. It occurs at the interface between fibre and matrix. When thefracture strain of the fibre is greater than that of thematrix, a crackwilloccuratthepointofstress. Ifthestress isnothighenough,thecrackwillbe retained. If the stress is too high, the crackwill pass around the fibrewithout breaking the adhesion bond. This local stress starts to increaselocally, resulting in a deformation of the fibre and matrix as the loadincreases[4].

Figure3Interfacialde-bondingIntralaminarcrackingThepropertiesofcompositesdifferregardingthedirectionofthematerial.In longitudinal direction, composite materials offer high stiffness andstrength.Howeverintransversedirection,thepropertiesaregenerallylow.


Thisresultsincracksalongthefibresofthematerialandisthefirstnoticedincompositematerials.Thesecrackscanoriginatefromdefectsinlaminatematerialswithplies,andgrowcrossesthethicknessoftheplyandrunningparallel to the fibres. The cause of this type of damage aremostly stressloading, fatigue, temperature changes or thermal cycling, which occursduringde-bondingoffibresormatrices,ormanufacturingerrors[5].FibrebreakageFibrebreakageultimatelyoccursinthematerial if it isaffectedbyfatigue,impact or manufacturing induced effects. The failure of composites iscausedbyfibresbreaking inthematerial. Individual fibreswill failat theirweakpointsandstresswillbedistributedbetweenmatrixand fibres.Thestress is then transferred from thebroken fibreby the interfacebetweenfibreandmatrixbacktothefibreatacertaindistance,resultingabreakageofanotherfibre.Thestressonfibres isenhancednearbytheplycracksofadjacentpliesduetothestackingofpliesinalaminate[5].VoidgrowthThe risk of defects are present not only during the operation withcomposite materials, but also during manufacturing. These defects areinduced in the fibre architecture. Voids are cavities found in all types ofcomposite materials. The formation of voids can be controlled bycontrollingmanufacturingparameterslikecure1temperatureandpressure,vacuum pressure and resin viscosity. Also, a void can occur during theimpact of a lightning strike,which releases thermal energy. Voids have asignificantimpactonthematerialbehaviour,mainlytheflexural,transverseand shear properties of the material degrade. Voids have a significantimpact on the behaviour of the material, regardless the volume andamount.Thecharacteristicsofavoid(shape,sizeanddistribution)playsaroleinmaterialdegradation[5].

1Curingishardeningandtougheningofpolymermaterialssuchascompositematerials

Figure4VoidfoundincompositematerialsDelaminationDelamination, also known as interlaminar cracking (Figure 5), are cracksthatoccur in the interfacialplanebetweenadjacentplies ina laminate. Itoccursatholesoratanexposedsurfacethroughthethickness.Thiscausesseparationof theplies.Delaminationoccursbecauseofdifferent reasons.Oneofthemisthatthelaminatedevelopsnormalandshearstressesatthesurface,freeoftraction,causinglocalcracksintheplanes.Thiscanalsobecausedbyplycracks,whichcancausetheseparationoftheregionbetweentwo adjacent ply cracks, due to fatigue. Another cause could be a low-velocity impact. In this case, the surface will appear undamaged, whiledelaminationcanoccurwithinthestructure.Ifthecrackisundetectedandthe structure is continuously loaded, the cracks will grow even larger,resultingthatthemechanicalpropertiesofthematerialwilldegradewhichcanleadtocatastrophicfailureofthestructure[5].

Figure5Delaminationinacompositematerial


DamagesonamacroscopiclevelDescribed as above, these damages occur in composite materials on amicroscopic level. These damages are not visible for the human eye,therefore not knowing of their presence if the material is not beinginspected. However, if the material is continuously being used foroperation without treatment, these microscopic defects will accumulateand cause damages on a macroscopic level. These damages requirecomplexand labour intensiverepairs,orevenreplacementofasectionofthe structure. This to prevent that the material properties will degradeduring operation and create a hazardous situation. Damages on amacroscopic level are cracks through the material or on the surface,scratchesthatremovedlayersofthematerialandinclusions.

RepairtechniqueswhicharecurrentlyusedintheaviationindustryInordertokeeptheaircraftairworthy,damages,asdescribedabove,mustbe repaired ifnecessaryandpossible.Thereareseveral repair techniqueswhich are used by the industry at the moment. Different aspects of thedamage, as described in the section above, such as dimensions andthickness, determinewhich repair technique is to be used.Also,whetherthe repair is on a primary or secondary structure is a factor. Primarystructuresare thosenecessary tosustain flight.A fewrepairmethodsareonlyusedasa temporarysolutionuntilamorepermanentrepair ismade[6].Forexample,acosmeticfillercanbeusedtorestoreasurfacetokeepfluidsout.Another solution canbea resin injection. This canbeeffectivewhen thedelamination is restrictedbetweenonly twoplies. Thematerialwill not gain much more strength, however, it does slow the spread ofdelamination. This factsheet will go deeper into the permanent types ofrepairmethodsforcomposites.Steppedco-bondedrepairThe stepped co-bonded repair method is a method where the damagedlayersareremovedinstepstoprovidealandingforthereplacementlayers[7]. Co-bonded means that two or more elements of which one is fully

curedandoneisuncuredarecuredtogether.Afterremovingthedamagedlayers,eachrepair layerwillthenoverlapitscorrespondingexposedlayer.Thismeansthat loadswillbedistributedthroughtherepairviaa lap jointintotheunderlyinglayersandthiscouldleadtopeakstressesattheedgesofeachstep.Furthermore,itrequirescoordinatedremovalofthestepsofeachlayer(whichtakesalotoftime),astheunderlyingpliesarenottobedamaged.Ontheotherhand,therepairsurfacewillonlybeslightlythickerthan originally and good intimate bonds can be achieved on the freshlyexposedsurfaces[8].An alternative for a co-bonded repair can be a secondary bond. Asecondarybondmeans that the two (ormore)pre-cured repair parts arejoinedtogetherbyadhesivebonding.Theonlychemicalorthermalreactionduring this process is the curing of the adhesive itself [15]. This methodrequires careful preparation of the bonding surfaces of each previouslycuredsubstrate.Also,itusuallyrequiresthatthepartsareverywellalignedwhichmeans that the fixturingandclamping isvery importantduring theprocess.TaperedscarfrepairTheideaofthetaperedscarfrepairisthesameasthesteppedco-bondedrepair, only now there are no actual ‘steps’ but the layers are exposedalongagentle slope [7]. The repair layerswill layover the correspondingexposed layers along this angle. The first advantage that comeswith thisrepairmethodisthattheremovalofthedamagedlayerscanbedonebyamachine, for example a drill. For a stepped repair this would be moredifficult.With bothmethods, film adhesive is used between thematerialandrepairplies.Also,theloadsaretransferreddirectlythroughtheedgesof the repair plies to the underlying structure. However, tapered scarfrepaircanbedifficulttoapplydependingontherepairconfiguration[9].Overall, the tapered scarf repair is considered to be an easier and bettermethodthanthesteppedco-bondedrepair.


Figure6ScarfrepairBoltedDoublerrepairAbolteddoublerrepaircanbeforexamplestainlesssteelortitanium.Thisrepairmethod isnormallyused formetal structural repairsand thereforereserved for thicker, solid and heavily loaded composite laminatestructures [4,8].At themoment this isoneofonlya fewrepairmethodsfor such structures. It is quite fast and easy compared to the other twomethods. However, the original damage is still present and the repairmethod simply attempts to direct the loads around this damage.Furthermore, when the doublers are from a different material than thematerialwhich is being repaired, thismay lead to problemsbetween theproperties of the materials, for example corrosion. Therefore when thismethodisused,thepartsneedtobeseparatedwithsealantorfilm.

Figure7BoltedpatchrepairRepairusingpre-cureddoublerSomecompositedamagescanberepairedusingpre-cureddoublers.Thisisa sheetofcompositematerialmade from layersof fibre-reinforcedepoxythat has been cured by using heat and pressure [8]. A patch with thecorrectdimensionsisthencutfromthepre-curedmaterialandbondedonto the surface of the damaged component. The edges are chamfered toincrease thepeeloff strength.Amajordrawback found in the industryatthemoment is that air can get entrapped under the doubler whichmaylead to a weak repair. This can be improved by using a layer of scrim(woven)clothundertheadhesivefilmtoallowtheairtoescape[8].


Whatarethedevelopmentsofnewtechniquestorepairdamagesoncompositematerials?Itcanbeseenfromthepreviouspartthatthecurrentrepairmethodshavesome disadvantages. This has to do with the Structural Repair Manuals(SRM).TheSRMcontainsthelimitstowhatextenttherepairofadamageisallowed to be performed. This is related to the ratio between thedimensionof thedamageanddimensionof thematerial. Incase that thedimensions of the damage exceeds the limits, the responsible companymustcontactthePart-21organisationtocomeupwithasolution.Besides,therearesomeothermajorchallengestoovercomewhenlookingatboththe safety and affordability viewpoint to improve the structuralmaintenance and repair technologies. The repair of composite materialsneed accurate processing techniques and trained technicians to preciselyimplementstandardprocedures(e.g.structuralrepairmanuals).Improvingrepairofcommercialaircraftcompositestructuresandcomponents is thegoal of the Commercial Aircraft Composite Repair Committee (CACRC).EASA makes sure that the standardization of the repair processes areconducted in a proper manner. Current research activities focuses onbonded composite repair and have globally gained the attention in thecomposite industryaswellas inacademia [10]. Thispartof the factsheetreviews developments of the material removal, surface preparation, theenvironmentalconditionsandthecurrentfocus.MachiningWhen a damage is found and assessed, this region must be machinedaccuratelytoremovematerialandtotaperedgesforimplementingbondedscarf repairs. But composite materials react very different and not aspredictableasmetals[11].Somachining/scarfing,inthiscasethematerialremoval, is complex and thus a key process in bonded scarf repairs.Accordingto[12],thequalityandaccuracyofthemachinedregionlargelydepend on the skills of a repair technician. Conventional machiningtechniquesarenotidealbecauseoftheappliedmachiningforcesandtoolgeneratedheatwhichcouldleadtomaterialdamage.Howeverthisprocesshas some opportunities to improve with the help of non-traditional

machining approaches such as pulse-laser and abrasive-waterjet basedtechniques.Thepulse-laserapproachoffersveryaccuratedamageremovalandscarfingof composites. Besides, themachinability is not affected by thematerialstrengthandhardness and thus lasermachining canbeadvantageous forheterogeneousmaterialssuchascomposites.Complexshapescanalsobemachinedmore easily because it is a non-contactmachining process, thepulse-lasermachinedoesnottouchthematerialsurface.Butontheotherhandacomputer-controlledlasermachiningsystemisrequiredtomachinedesigned scarf angles and shapes to overcome disadvantages like largeheat-affected zones (HAZ) and health risks [10]. The abrasive-waterjetbased techniqueusesawaterjet incombinationwithabrasiveparticlesathighspeed.Thiswaterjetpumpswaterwithhighpressurethroughanozzletoformacoherentstreamflowingathighspeed,whichachievesgeometricaccuracytomachinecompositematerials(Momber&Kovacevic,ascitedinKatman et al, 2013). Again this technique provides accurate damagedregionremoval,butitalsoeliminatestheissueofheat-affected-zonesandtool wear. Further it is environmental friendly [13] and eliminates toxicfumes. But for on-aircraft bonded repair these abrasivewaterjet systemsrequiresacomplexsetupandcouldalsobeexpensive.SurfacetreatmentSurface treatment is the process of cleaning and preparation of thematerial prior to bonding and is crucial for strong adhesion between thefibre andmatrix phases. There is not a single theory or mechanism thatexplains the chemical andphysicalmanifestationsof theadhesionand sothis principle is not fully understood yet [14]. A misconception aboutadhesion for example is that a clean surface is the only requirement forbetteradhesion.However,asurfacetreatmenthastomodifythephysicaland chemical properties of the surface, increase the surface energy andremovecontaminantsandweakboundarylayers(FourcheandWingfeld,ascited in Katman et al, 2013). These requirements will lead to a strongerbonding and it improves structural performance. Current surfacetreatmentsarenot ideal,becausetheycouldadverselyaffectthebonding


properties. Advanced surface treatments like atmospheric plasma andpulsed laser ablation are possible ways to improve these bondingproperties.Plasma treatment in de first place exposes the polymer surface to lowpressureplasmaoratmosphericplasmawhichconsistsofchargedparticles.Thisplasmamodifiesthesurfacepropertiesand improvestheadhesion incompositebonded joints.Butthesetreatmentsrequireexpensivesystemsin comparison to the conventional surface treatments (abrasion cleaning,gritblastingetc.). Inthesecondplacethere istheopportunityto improvethe chemical and physical properties by the application of a lasertreatment. As discussed before, lasers provide a controlled non-contactprocess and provide opportunities for uniformity, repeatability andautomation[10].Againthisprocessisverycomplexandrequiresexpensivesystems.Butthinkabouttheopportunitytousealaserfordamageremovalandsurfacepreparation;thatwouldbeonebigstepforward.


EnvironmentalconditionsA very important factor during the repair of composite materials arecontrolledcuringconditions.Applyingtherighttemperature,pressureandvacuum conditions is essential to the curing process and to ensure goodcompactionofthelaminateplies[10].Withoutcontrollingtheseconditionsthemolecularstructurecanbechanged,moreporositycouldariseandthiscan lead to inadequate consolidation of the composite material whichaffectsthemechanicalproperties.Oneofthecurrentdevelopmentsisthatcomposite repaircompanies likeAirborneServicesdesignacleanroom inwhich the temperature, pressure andhumidity is kept constant. AirborneServices, located at the Main Support Base Woensdrecht, currentlymaintains therotorbladesof thehelicopter fleetof theRoyalNetherlandAir Force. They are building a fixed clean room that filters the air andappliesclimatecontrol.Thesecleanroomsarealreadyappliedmoreoftenduringthemanufacturingprocessesofnewproducts,butrepaircompaniesareusingitmoreandmoretoimprovethequalityoftheirrepairprocessesaswell.ThecurrentfocusCurrent developments are focusing more on the whole repair processinstead of new repair methods as displayed in this factsheet. Realizingoptimizations of the current repair processes, like machining, surfacepreparation and the environmental conditions is easier to conduct thanimplementing whole new repair methods, because of the strict aviationregulations.Companiesarealsomoreinterestedinwelltrainedpersonnel,becausehumanfactorsareacrucialfactorintherepairprocess.Soanotherfocusing point is the training of personnel to the required level forconductingtherepairofcompositematerialsinaproperway.


References1Boeing (2010). First flightof the787wasa timeofhighemotions for the787 team and Boeing employees around the globe, captured here inpictures by Lori Gunter. Retrieved from:http://www.boeing.com/news/frontiers/archive/2010/february/cover.pdf2Ee, S. van. (2015). Composites Fact Sheet. Geraadpleegd vanhttp://aviationfacts.eu/uploads/thema/file_en/54b9339170726f67dc000000/Composites_Fact_sheet.pdf3Marine composites (2nd ed., pp. 181-182). (1999). Annapolis, Md.: EricGreeneAssociates.4Talreja,R.,&Singh,C.(2012).Damageandfailureofcompositematerials.Cambridge:CambridgeUniversityPress.5Aslan, Z., Karakuzu, R., & Okutan, B. (n.d.). The response of laminatedcompositeplatesunderlow-velocityimpactloading.CompositeStructures,119-127.6Types of Repair. (n.d.). Retrieved November 11, 2015, fromhttp://www.netcomposites.com/guide-tools/guide/repair/types-of-repair7Dorworth, L.C. (2007). Essentials of Advanced Composite Repair[Powerpointslides].Retrievedfrom:www.abaris.com

8Composite Repair. (1999). Retrieved November 11, 2015, fromhttp://www.hexcel.com/Resources/DataSheets/Brochure-Data-Sheets/Composite_Repair.pdf9Bendemra,H., Compston,P.,&Crothers, P. (2015).Optimisation studyoftapered scarf and stepped-lap joints in composite repair patches.CompositeStructures,1-8.10KatnamK.B.,DaSilvaL.F.M.,YoungT.M.,2013.Bondedrepairofcompositeaircraft structures: A review of scientific challenges and opportunities.ProgressinAerospaceSciences61:26–42.11Sloan J., 2010. Machining carbon composites: risky business. HighPerformanceComposites.12MasonK.,2005.Thecraftofaircraftrepair.HighPerformanceComposites.13Awaja F, Gilbert M., Kelly G., Fox B., Pigram P.J., 2009. Adhesion ofpolymers.ProgressinPolymerscience34:948–968.14Sheikh-Ahmad J.Y., 2009. Machining of polymer composites. NewYork:Springer.15Hoke, M. J. (n.d.). Adhesive bonding of composites [Powerpoint slides].Retrievedfrom:www.abaris.com


ImagereferencesCoverhttp://www.bloomberg.com/photo/boeing-seeks-to-seal-documents-in-labor-case-over-787-plant-/89675.html1http://www.boeing.com/news/frontiers/archive/2010/february/cover.pdf2http://www.dailytech.com/Two+More+Boeing+787+Dreamliners+Catch+Fire+Suffer+Technical+Issues/article31962.htm3Talreja,R.,&Singh,C.(2012).Damageandfailureofcompositematerials.Cambridge:CambridgeUniversityPress.Page38.4http://materialstechnology.asmedigitalcollection.asme.org/article.aspx?articleid=14281645http://rutgersscholar.rutgers.edu/volume01/pelestra/pelestra.htm6http://www.netcomposites.com/education.asp?sequence=757https://www.dsiac.org/resources/dsiac_journal/winter-2015-volume-2-number-1/contemporary-methods-repairing-composite

AcknowledgmentThis fact sheet was written using funding of SIA-RAAK as part of theCOMPL-AIDproject,contributingtotheknowledgeoncompositerepairs.


DutchsummaryComposietenzijnindeloopdertijdgeïntroduceerdalshethoofdmateriaalvoor nieuwe vliegtuigen, zoals de Boeing 787 Dreamliner en de AirbusA350.Composietenhebbeninvergelijkingmetdehuidiggebruiktemetalenzoalsaluminiumbetereeigenschappenzoalsmeer sterkteen stijfheid tenopzichtevanhunsoortelijkegewicht.Echter,composietenhebbenanderesoortenschadediebepaaldereparatiesnietmogelijkmaken.Dezeschadeontstaat door vermoeiing van het materiaal tijdens operatie, zoals eenbotsingmetvoorwerpen,entijdensfabricage.Desoortenschadesontstaanopmicroscopischeschaalzoalshetontbindenvande interface,scheurtjesin transverse richtingen inde vezels, inclusies endelaminatie. Indienhetmateriaal nog steeds wordt gebruikt voor operatie, dan zullen dezemicroscopische defecten uitgroeien naar macroscopische defecten zoalshetverdwijnenvan lagen inhetmateriaal,scheurtjesdiezichtbaarzijnophetoppervlaken inclusies.Hiervoorzijnverschillendereparatietechniekenontwikkelddieuitgevoerdwordenomdeluchtwaardigheidtewaarborgen.Welke technieken er worden gebruikt hangt af van de dimensie van deschade en of het beschadigde materiaal een deel van de primaire ofsecundaire structuur is. Daarnaast moeten de reparaties in accurateprocessenwordenuitgewerktmetbehulpvanverschillendehandleidingenendoorgetraindpersoneel.Dehuidige reparatietechniekenhebben iederhun beperkingen en dat zorgt er voor dat niet alle schades gerepareerdkunnen worden. Tot hoever een materiaal met een specifieke schadegerepareerdmagworden,staatbeschrevenindeStructuralRepairManual.HetdoelvandeCommercialAircraftCompositeRepairCommittee(CACRC)ishetverbeterenvannieuwereparatietechnieken,zoalshetgebruikenvaneenextracomposietenplaatalsafdichting.Daarnaastwordtgekekennaarniet conventionele machining methodes, die minder warmte creëren ennauwkeurigerzijn.Ookzijnerbedrijvendieopditmomentwerkenaanhet

verbeteren van de oppervlaktebehandelingen. Bij de reparatie speelttegenwoordigdeomgeving tevenssteedseengrotere rol.ZowordteropditmomentbijAirborneServicesopWoensdrechteencleanroomingerichtom de condities tijdens de reparatie onder controle te houden en zo demoleculaire structuur van de composietmaterialen te waarborgen. Alslaatst zorgt de European Aviation Safety Agency (EASA) er voor dat dereparatieprocessen worden gestandaardiseerd. De huidige focus bijbedrijven ligt op het complete proces, vanwege de strikte regelgevingomtrentnieuweapparatuurenmethodes.

ThisisaLuchtvaartfeiten.nl/AviationFacts.eupublication.Authors:Hogerbrug,M.,Koc,K.,Zandvliet,C.Editorialstaff:R.J.deBoerPhDMsc,G.BoostenMSc&G.J.S.VlamingMScCopyingtextsisallowed.Pleasecite:‘Luchtvaartfeiten.nl(2016),RepairofCompositesFactsheet,www.luchtvaartfeiten.nl’Luchtvaartfeiten.nlisaninitiativebytheAviationAcademyattheAmsterdamUniversityofAppliedSciences(HvA).Studentsandteachersshareknowledgewithpoliticiansandthegeneralpublictoensurediscussionsarebasedonfacts.February2016

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Repair of Composites Fact sheet - African Slum Journalaviationfacts.eu/.../Repair_of_Composites_Fact_sheet.pdf · Repair of Composites Fact sheet Introduction ... , the Airbus A350