1. Technological Education Institute of Larisa, School of Mechanical Engineering GR 41110-Larisa, Greece2. Hellenic Military Academy, Vari, Attika, Greece

Dionysios E. MouzakisDionysios E. Mouzakis1,21,2, Stefanos Zaoutsos, Stefanos Zaoutsos11

Deformation and Fracture of Composites (DFCDeformation and Fracture of Composites (DFC--11) 11) &&Structural Integrity and MultiStructural Integrity and Multi--scale Modelling (SIscale Modelling (SI--5)5)Queens’ College, CambridgeQueens’ College, Cambridge1313--15 April 201115 April 2011

Introduction-Problem Statement Experimental Procedures

MaterialsDynamic Mechanical AnalysisThree Point Bending Tests

Results & Analysis 3PB Graphs and Flexural Properties DMA data analysis SEM study of flexural specimens Damage Detection Perspectives Conclusions

ByBy thethe endend ofof thethe presentpresent decadedecade atat

leastleast threethree longlong rangerange passengerpassenger--

commutercommuter airplanesairplanes shallshall bebe mademade

availableavailable inin thethe openopen marketmarket

featuringfeaturing largelarge partsparts ofof compositescomposites..

••BoeingBoeing 787787 “Dreamliner”“Dreamliner” ((5050%%

carboncarbon composites)composites) isis aboutabout toto

enterenter serviceservice..

••MitsubishiMitsubishi MRJMRJ ((1515%% carboncarbon

composites)composites) droppeddropped compositecomposite

wingwing andand airframe,airframe, entersenters serviceservice

20132013..

••AirbusAirbus 350350 XWDXWD ((5353%% carboncarbon

composites)composites) willwill enterenter serviceservice byby

20132013 ??

Almost all these airplanes feature fuselages composed of Almost all these airplanes feature fuselages composed of large monolithic carbon fiber reinforced composite parts.large monolithic carbon fiber reinforced composite parts.

…………Mitsubishi’s shock announcement overnight says compositeswill now be restricted to a maximum of around 15% of the structure,mainly in the tail and other areas where composites have been usedby jet makers for nearly 30 years.It is excluding the material from those areas where complex loadbearing stresses will occur, particularly in high cycle operations suchas regional services where the jet may experience up to 12 landingsor takeoffs and pressurisations a day.

A Mitsubishi spokesperson says, “ Structural changes are easier andrequire shorter lead times with aluminium wings. With an aluminiumwing box, the wing structure can be more easily optimised for thefamily …………………………..

Detrimental Issues (sic):Detrimental Issues (sic):1. What about their long term 1. What about their long term fatiguefatigue life.life.2. What about their long term mechanical properties 2. What about their long term mechanical properties when exposed to when exposed to environmental aging environmental aging ..3. What about their long term viscoelastic behavior 3. What about their long term viscoelastic behavior ((creep and creep fatigue creep and creep fatigue and its impact on mech. and its impact on mech. response.)response.)4. 4. ImpactImpact damage (low and high energy)damage (low and high energy)5. Can 5. Can damagedamage accumulation due to the above accumulation due to the above reasons be reasons be detecteddetected during induring in--flight operation ? flight operation ?

Composite Laminates were prepared by Vacuum Assisted Resin Infusion Molding in stacked woven carbon fiber layers, cured for 12h@ RT

Resin type R2940/Infusion RTM (E=3,6 GPa, σult ≈ 70-85 MPa, Tg ≈ 67-80 oC )

Fabric type: C400P (TR50S) Plain Weave,(E= 240 GPa, σult=4,9 GPa)

Quasi isotropic Plates 400x400x6 layers(t≈ 2,50 mm) [(0/90)2/45]s

Supplier: Fibermaxcomposites

Composite Plaques were aged for 12 daysIndwelling for 24hrs @ 50o C, RH=65%Followed by 24hrs @-40o C

Specimen Length:Specimen Length: 50 mm, 50 mm, Width=15 mmWidth=15 mmCrosshead speed V=2,1 mm/minCrosshead speed V=2,1 mm/min

Lo=40mmLo=40mm

(DMA) 3 point bending on slabs (t~2.5 mm), T=0-250 oC , f=1,10,50Hz, T=3 oC/min , Δl=15 μmDMA Q800 ΤΑ Ιnstruments

Specimen Length: 60 mm, Width=12 mmSupport Span:50 mm

AA.. HodzicHodzic ,, JJ..KK.. KimKim ,, AA..EE.. LoweLowe ,, ZZ..HH.. StachurskiStachurski,, CompComp.. SciSci.. TechTech.. 6464 ((20042004)) 21852185––21952195““TheThe decreasedecrease ofof RR--curvecurve correspondedcorresponded moremore toto degradationdegradation ofof thethe interphaseinterphase mechanicalmechanicalpropertiesproperties manifestedmanifested byby thethe decreasedecrease inin hardnesshardness andand increaseincrease inin widthwidth ofof thethe interphase”interphase”

DD..EE.. MouzakisMouzakis ,, HH.. Zoga,Zoga, CC.. Galiotis,Galiotis, CompositesComposites:: PartPart BB 3939 ((20082008)) 467467––475475…………………….. inin epoxyepoxy resins,resins, waterwater hashas provendprovend toto bebe responsibleresponsible forfor thethe creationcreation ofof aasecondarysecondary networknetwork ofof crosscross--linkslinks betweenbetween freefree hydroxylshydroxyls ((--OH)OH) ofof thethe mainmain chainchain ofofthethe resinresin.. Therefore,Therefore, waterwater moleculesmolecules dodo notnot actact asas plasticizers,plasticizers, asas expected,expected, butbut inincontrastcontrast makemake thethe polymerpolymer somewhatsomewhat stifferstiffer.. ThisThis isis alsoalso markedmarked byby aa shiftshift ofof thethe TgTg atathigherhigherTemperaturesTemperatures..

Three Point Bending Tests in Three Point Bending Tests in Pristine SpecimensPristine SpecimensMechanical Testing

Mechanical Testing

Three Point Bending Tests in Three Point Bending Tests in Pristine SpecimensPristine Specimens

E-modulus σy* εy* σΒ εΒ

[MPa] [MΡa] [1] [MΡa] [1]

Pristine 19747,26 591,8 0,041 706,9 0,05

error 5130,84 100,1 0,003 74,79 0,007

Aged 17574,52 562,6 0,042 668,8 0,05

error 2143,51 69,83 0,001 63,04 0,003

* Stress and strain at first crack event

DMA DATADMA DATA StorageStorage Modulus ComparisonModulus Comparison

Tg migration ?

Minor decrease of the E’ for Temperatures<Tg

DMA DATADMA DATA LossLoss Moduli ComparisonModuli Comparison

Tg migration ?

E’’ becomes lower sign of less energy dissipation per cycle load

DMA DATADMA DATA tantanComparisonComparison

Tg migration ?

Damping coefficient of the materialbecomes lower

Pristine Samples from three point bending tests

DelaminationDelaminationAppears to beAppears to bethe governingthe governingFailure Failure Mechanism hereMechanism hereFacilitated by theFacilitated by thePresence of fiberPresence of fiberBundles in the Bundles in the Woven layersWoven layers

MatrixMatrix--fiberfiberInterphase Interphase appearsappearsRelatively goodRelatively good

Aged Samples from three point bending tests

DelaminationDelaminationCorroborated byCorroborated byIntralayer crackingIntralayer crackingappears now appears now As the Failure As the Failure Mechanism in theMechanism in theAged composites.Aged composites.

MatrixMatrix--fiberfiberInterphase Interphase appearsappearsRelatively fairRelatively fair

Application of magnetoelastic sensors[Mouzakis DE, Dimogianopoulos D, in preparation]

DMA Q 800, TA InstrumentsEMF Data collected via PC in

unfiltered state

Carbon/Epoxy Slab MetGlas Stripe

DetectingCoil

3PBClamp

Material: Carbon Epoxy Slab: 60x12x2.16 mm3

16 plies, woven non crimp [0/90]16

100 cycles of Thermal Fatigue -27 to +50oC

(a)

Figure 1: (a) Schematic of the experimental set up with the shaded area indicating the

inflicted stochastic damage due to thermal fatigue; (b) DMA dynamic loading chart with

the vibration amplitude (left y-axis) and the slab response (displacement, right y-axis)

versus time.

(b)60

50

40

30

20

10

0

-10

Am

pli

tud

e (

m)

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00

140

120

100

80

60

40

20

0

-20

Dis

pla

cem

ent

(m

)

Time (min)

Sinusoidal Excitation Input of Sinusoidal Excitation Input of Increasing AmplitudesIncreasing Amplitudes

Statistical

decision-making:

COMPARISON

b/w current AR

& healthy AR

Mechanical and Viscoelastic Response of Aged Carbon/Epoxy VARIM composites

••ThreeThree pointpoint bendingbending testingtesting hashas shownshown thatthat inin thethe earlyearly stagesstagesofof environmentalenvironmental agingaging inin wovenwoven carboncarbon fabricfabric /epoxy/epoxy reinforcedreinforcedcompositescomposites::••aa.. FlexuralFlexural modulusmodulus andand strengthstrength showshow aa deterioratingdeterioratingbehaviourbehaviour..••bb.. ViscoelasticViscoelastic propertiesproperties indicateindicate aa shiftshift ofof thethe glassglass transitiontransitionpossiblypossibly attributedattributed toto bothboth postpost curingcuring andand secondarysecondarycrosslinkingcrosslinking.. Also,Also, dampingdamping coefficientcoefficient isis beingbeing reducedreduced..••SEMSEM fracturefracture analysisanalysis hashas shown,shown, thatthat inin nonnon--agedaged mechanimsmechanimsthethe prevailingprevailing failurefailure mechanismmechanism isis delaminationdelamination andand afterafter agingagingintralayerintralayer crackingcracking appearsappears..

Damage detection & assessment

MagnetoelasticMagnetoelastic sensingsensing coupledcoupled withwith stochasticstochastic signalsignal analysisanalysiscancan detectdetect damagedamage duringduring actualactual operationoperation BUTBUT…………....--ISIS THETHE TYPETYPE OFOF DAMAGEDAMAGE OROR THETHE DAMAGEDAMAGE MECHANISMMECHANISMDETECTABLE?DETECTABLE?--CANCAN THETHE SENSORSENSOR SIGNALSIGNAL BEBE CORRELATEDCORRELATED WITHWITH THETHE ACTUALACTUALDEGRADEDDEGRADED MECHANICALMECHANICAL PROPERTIES?PROPERTIES?

MagnetoelasticMagnetoelastic signalsignal cancan bebe detecteddetected inin aa nonnon--contactcontact mannermannerandand bebe furtherfurther transmittedtransmitted forfor processingprocessing (Zigbees(Zigbees ?)?) andand surelysurely ititprovidesprovides aa usefuluseful alternativealternative toto thethe FiberFiber BraggBragg GratingsGratingstechniquetechnique werewere “wiring”“wiring” ofof thethe airstructureairstructure isis neededneeded..