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Serbi

A NANOF T

1Aristot

3Aristot

Abstract:Threinforcemeof carbon nthis work wagreement bnanoscale enanotube rewith the resdata were cwere compalayer interathe models a Keywords: Properties, 1. INTROD

Epoxy n(CNTs) hfollowing t1991[1].CNdue to multifunctiowith the honano-scale shown remaand strengaddition of the various [4] have intensile and epoxy reinshown thatSWCNTs (increased Y

ian Tribology Society

NOMECTHE EL

CAR

tle University

tle University

he mechanicaents is investnanotubes hawas to investbetween the experimentaeinforcementsults obtainecorrected resared with theactions of theand the expe

NanoindenMicroscopy

DUCTION

nanocomposihave been the successf

NTs have attrtheir uniq

onal propertosting matrix

features. arkable enhagth of polyf small amou

studies inconvestigated t

thermal pronforced nant the additi(0.25 wt.%)

Young’s mod

SE13

K

CHANICLASTIC RBON N

G. y of Thessalon

2Internationof Thessalon

al behaviourtigated in theave been chatigate the effmechanical l methods. Ht of 1%. Theed from the nsulting to one Halpin-Tsae nanotube w

eriments.

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ERBIA3th Internati

T

Kragujevac,

CAL APPPROPE

NANOTU

Mansour1, Dniki, Departmenal Hellenic Uiki, Departme

r of nanocome present paparacterized foficiency of thproperties o

Higher incre modulus ananoindentanly a 3% diffai model andwith the hos

ing, Epoxy

arbon nanotuy investigais of CNTsderable attennical, surfong interactisociated to tperiment shelastic modu

osites with Ts [2,3]. AmNTs, Loos etiffness role

carbon nanotes. They hmall amountmatrices, grensile strength

13th I

ATRIB

ional ConfeTribology

Serbia, 15 –

PROACHERTIES UBE NA

D. Tzetzis2, ent of Mechan

University, Greent of Mechan

mposite mateper. Epoxy nfollowing tenhe reinforcemof the epoxy rease in moas measured ations, howevfference. Thed with the T

sting matrix.

Nanocompo

ubes ated, s in ntion face, ions their have ulus

an mong et. al e on tube have t of eatly h of

suctenmonanstudrheCNby treadispintenanexhviscbechomintemainflme

nternational C

B ‘13rence on

– 17 May 20

H ON TOF EPO

ANOCO

K.D. Bouzanical Engineereece, d.tzetzisnical Engineer

erials with manocomposisile tests andment providenanocompodulus was aby the tensi

ver by utilisie modulus reThostenson-C

Arelatively

osites, Mult

ch nanocompsile properti

ore influencnotubes thandied the ef

eological aNT/epoxy com

acid treatmatment. The persed in terfacial bondnocomposite hibited highecosity than cause the mogeneous eraction bettrix. Gojny luence of dchanical

Conference on

Facu

13

HE MEAOXY REMPOSIT

kis3

ring, Greece, m@ihu.edu.gr ing, Greece, b

ultiwall carbtes with diffed nanoindened by nanotusites obtaineaccomplishedile tests diffeing a properesults obtaineChou model a

good agreem

tiwall Carb

posites. The es of soft ep

ced by then stiffer onesffects of suand mechamposites. Th

ment, plasmasurface mo

the epoxy mding with th

containinger storage an

those withsurface treadispersion o

tween the Cet al. [6]

different typroperties

n Tribology –

ulty of Enginein Kragujevac

ASUREEINFORTES

mansour@eng

bouzakis@eng

bon nanotuberent weight ntations. Theubes and to ed via a macd at weightered an averr calibrationed from the accounting fment was fou

bon Nanotub

results showpoxy matrice addition s. Also, Kimurface modianical prohe CNTs wea oxidation, odified CNTmatrix and he polymer g the modind loss moduh the untreatments proof CNTs aCNT and t

have inveypes of CN

of epo

Serbiatrib’13

ering c

MENT CED

g.auth.gr

g.auth.gr

e (MWCNT)percentagesobjective ofexamine the

croscale andt fraction ofrage of 18%n method the

experimentsfor the outerund between

bes, Elastic

wed that thees are much

of carbonm et. al. [5]ification on

operties ofere modified

and amines were wellhad strong

matrix. Theified CNTsuli and shearated CNTs,ovide moreand strongerthe polymerstigated the

NTs on thexy based

) s f e d f

% e s r n

c

e h n ] n f d e l g e s r , e r r e e d

13th International Conference on Tribology – Serbiatrib’13 365

nanocomposites. The influence of filler content, the varying dispersibility, the aspect ratio, the specific surface area and the functionalisation on the composite properties was correlated to the identified micro-mechanical mechanisms. The results showed that the produced nanocomposites have enhanced the strength and stiffness along with an increase in fracture toughness.

Despite the huge amount of experimental data available in the literature there are still debatable results concerning the elastic property and strength of such nanocomposites. This is due to the characteristic difficulties inprocessing the CNT nanofillers in polymer systems, and thereby a reliable theoretical correlation of the experimental data is still lacking. This is because the reinforcement capability of the CNTs in a polymeric matrix will depend on their amount as well as on their arrangement within the matrix which plays a fundamental role in the load transfer mechanism.

On the other hand, in context with the high prices of the CNTs, there is a requirement for procedures using small samples of nanocomposites, compared to the standard tensile test samples, in order to acquire mechanical property data on which theoretical predictions can be based. Therefore, alternative approaches have been utilised for determination of the mechanical properties of nanocomposites [7]. Nanoindentation is a simple but powerful testing technique, which can provide useful information about the mechanical properties (such as elastic modulus and hardness) of materials. It has been proven that the nanoindentation technique is the most accurate method for evaluation of the effect of carbon nanotubes on the deformation behaviour [8].

The aim of this work was to investigate the mechanical properties of MWCNTpolymer composites by nanoindentation. Elastic modulus and hardness are the properties measured by the nanoindentation technique and these were compared by results obtained by uniaxial tensile tests as well as with popular arithmetic predictions. The morphology of the nanocomposites was investigated by using a stereomicroscope and scanning electron micrographs.

2. MATERIALS

The epoxy matrix investigated was a low

strength bisphenol A and epichlorohydrin epoxy resin (Epikote 816, Hexion Specialty Chemicals) containing an added proportion of Cardura E10P (glycidyl ester of neodecanoic acid) as a reactive diluent. The hardener was amine curing agent (Epikure F205, Hexion Specialty Chemicals). The

nanofiller used, was multiwall carbon nanotubes (MWCNT’s). The carbon nanotubes were used as-received without any further treatment.

Epoxy-based nanocomposites were prepared by mixing the nanotubes with an appropriate amount of the neat epoxy resin using an ultrasonic stirrer (Bandelin Electronic GmbH, model HD2200) for 5min followed by high mechanical mixing. This was followed by the addition of the hardener and further mechanical mixing. The mixture was degassed and then cast into release-agent-coated special formed moulds in order to form the plates for specimen fabrication. The plates were left to cure for 48hours followed by 2 hours post curing at 90ºC. As a result, a series of specimens with nanofiller contents of 0.5% and 1% by weight were obtained. Small specimens of 10x10mm were cut from the plates and polished in order to make the nanoindentation specimens. 3. EXPERIMENTAL PROCEDURES

3.1 Tensile Tests

Tensile tests were performed at room temperature (23°C) on a Zwick Z010 (Zwick, Germany) universal testing machine at a constant crosshead speed of 1 mm/min. The measurements followed the EN ISO 527 testing standard using dumbbell shaped specimens. The specimens having a 4 mm thickness were machined from the moulded plates using a Computer Numerical Control (CNC) milling machine. The overall length of dumbbell specimens was 170 mm. The length and width of narrow section were 10 and 4 mm, respectively. E-moduli were calculated within the linear part of the stress-strain curves. All presented data corresponds to the average of at least five measurements.

3.2 Nanoindentation Testing

Nanoindentation tests involve the contact of an indenter on a material surface and its penetration to a specified load or depth. Load is measured as a function of penetration depth. Fig. 1 shows the typical load and unloading process showing parameters characterizing the contact geometry. This schematic shows a generic viscoelastic-plastic material with the loading OA, and unloading AB´ segments. The plastic work done in the viscoelastic-plastic case is represented by the area W1 (OAB´). The area W2 (ABB´) corresponds to the elastic work recovered during the unloading segment. In the case of purely elastic material, the unloading curve is a straight line (AB) and hr=hmax (W2=0). In this case, penetration depth is the displacement into the sample starting from its surface. Numerous details on the nanoindentation

366

measuremenfound in ref

In the cconducted oresolution odiamond tipwith a triincluded annanoindentaspecimens shown in indenter wtoward the indenter waaround 0.60.15mN/s, uand subsequthe same ra(in order tdeformationproperty meunloaded, to

The camodulus annanocompoand Pharr nanoindentapenetration

Where Pmax at the maxithe projectethe specimecan be expindentation

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[12]. Accoation hardnedepth of ind

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s hardness Hfrom the set o

n Tribology –

depends on tBerkovich

tic modulus (

the elastic mly, for the iond indenter

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hr is the residuent of the surfntact indentati

e loading and (half-section)

entation depth

H and elasticof equations g

Serbiatrib’13

(5)

the geometryindenter, β

(Es) can then

(6)

modulus andindenter andr, Ei is 1140

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13th Internati

4. RESUL 4.1 Morph

Microscoepoxy nano

Figure 3. Stwith nanotu

The nanwhich is mnanotube lointeractionsdispersion dsubsequent formation cmatrix whiattract eachseen from clusters obsirrespectiveslightly higevidently processing ultrasonic mdark solutiorelatively dnanovoids cthe degassinperiod the

ional Conferen

TS AND DI

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ope images composites a

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notubes showmore pronouoading due

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mechanicacould only ile these agh other formthe images.

served in all e of the pgher densitiefor the 1of the e

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nce on Tribolo

ISCUSSION

from the of are shown in

mages of epoxyations of: a) 0.

w significantunced in the

to strong to relativeltrasonic app

al mixing. be achievedggregates aming greater

The structuspecimens wercentage les of partic1%wt nanoepoxy nanoduced a frotde the degasso, it is bee eliminated re and as durix can react

ogy – Serbiatr

N

cured MWCn Fig. 3.

y nanocompos5%wt, b) 1%w

t agglomerae case of 1%van der W

ely insufficplication and

An aggregd in the ept certain arr assembliesure of nanotwas very simoading, thocle clusters ocomposites.ocomposites thy and viscssing procedelieved that

in total desuring the curt only with

rib’13

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sites wt.

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The stresnocompositese specimenshaviour.

gure 4.Typicaepoxy

The additionstrength as

cture surfacamined usine pure epoxyer lines and

a). This typettle epoxy suontaneous onitored durin

Fig. 5(b) shm the MWces the fract the nanotubult, when thbonding may

formationstuous surfaceDuring the

local streWCNTs (Figditionally, bmerous micrt specimen ae aggregatesich in turn lding of the mThe nuclea

veloped eitheWCNTs that at the aggreg

nanotube agge nanovoids

sts

ss–strain s under tenss revealed

al uniaxial teny reinforced n

n of the MWs reported ines of the tg a scannin

y resin sampla smooth su

e of fracture urfaces indiccrack propng tensile tesows the frac

WCNT nanture is a mibes were noe external te

y have occurs of clustere with certainapplied ma

esses aroun. 5c) triggere

before the onrocracks weras visually m may have imay have t

matrix. ation of ther within nehave not inf

gates’ interfac

gregatesthe inside the a

behaviour sion is showa character

nsile stress-strananocomposite

WCNTs slightn other studtensile specng electron les showed curface as sh behaviour icating low rpagation wsting of speccture behavionocompositesirror-like wh

ot dispersed eensile force wrred at these rs produced n yielding reacroscopic tend the agged yielding onset of a crre formed onmonitored duinduced cractriggered m

he cracks etwork of thefiltrated withaces.

367

matrix itselfgglomerated

of thewn in Fig. 4.ristic plastic

ain curves of es.

tly increasedies [2]. The

cimens weremicroscope.

characteristichown in Fig.is typical ofresistance towhich wasimens. our obtaineds.In certainhich reflectsevenly. As awas applied,areas. Also,a severely

egions. ensile stressgregates ofof the epoxy.ritical crack,n the tensile

uring testing.ck branchingultiple local

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7

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368

4.3 Nanoin

Fig. 6 curves of inload of 4.8MWCNT nduring indewere found

The indefrom aroundepths arnanocomposamples. Tincreased awell docummodulus haloading of M

There imodulus atesting comshown in Ta

Clearly nanoindentahigher than

Table 1. Eexperiments.

The proc

a relativelypolymeric various studmay be tooproperty foAlso, the naelastic behaviscoelasticcalculation are uncertadirectly relmaterial dewhich is alwin the fabricthe assessmtested surfaexacerbatedrequires a smaterial at vblunting effpenetrationstip/machineindentationsextrapolated

Material

0% CNT

0,5%CNT

1%CNT

ndentation

illustrates ndentations

8mN on the anocompositentation as on the loadientation dep

nd 0.5 to 0re observe

osites as comThe hardnesas the concemented in thas an increasMWCNTs is is a signifis obtained

mpared to theable 1. the elastic m

ation testingthe one obta

Elastic modu

cess of nanoiy complicatematerials asdies [11, 14

o low to meor ‘soft’ matanoindentatioaviour of thc behaviour

of the elastiainties in tate to the a

ependent in mways presentcation of the

ment of the mace at the fid by the caseries of indevarious deptfect on the cs, which doe behavious and so d may not

Etensile (GPa)

3,3 ± 0,12

4,5 ± 0,15

4,64 ± 0,18

typical loamade at a ppure epoxy

tes. No cracno steps orng curves.

pths at the p0.6 μm. Lowed for t

mpared with ss and elastentration is he literature sing trend asincreasing [

icant differefrom the

e one of the

modulus obtg techniqueained from th

uli values a

indentation me procedure,s it has be

4]. The systasure the mterials like ton techniquee test matermay cause

ic modulus. Mtip shape carea functionmost cases. t due to technindenter, ma

mechanical pirst material alibration prentations upoths and producalibrated tipo not corresur at th

the final be exact.

Enanoindentati

(GPa) 3,9 ± 0,12

5,22 ±,0,1

5,31 ±,0,2

ad–displacempeak indentay resins and cks were formr discontinui

peak load rawer indentathe MWCthe pure ep

tic modulusincreased. Ithat the ela

s the percent13]. ence in elananoindenta

e tensile tests

tained from e was 14-1he tensile test

as derived f

measurement, especially een reportedtem complia

material respohe epoxy re

e is based onrial; thereby an error in Moreover, thcalibration n (A) whichThe tip def

nical limitatiay greatly afproperties of

layers. Thirocedure whon the refereuces an intrinp at the deepspond with he shallow

area funcTherefore,

ion Emodified(G

2 3,37

8 4,57

22 4,75

13th I

ment ation

the med ities

ange ation CNT poxy s is It is astic tage

astic ation s as

the 18% ts.

from

ts is for

d in ance onse esin. n the

the the

here that h is fect, ions ffect f the is is hich ence nsic pest the

west ction

the

intrdiffsurcur

Figo

distcrathainvwelnotdocmothe

GPa)

nternational C

rinsic errorsficult to explrfaces like rrent case.

gure 5. SEM mof a) pure epo

Also, for antorted surfacter of the nat the typi

volves calibrll-defined elt suitable cumented byodulus betwe

uniaxial ten

Conference on

s may leadlain in the cathe solidifie

micrographs oxy resin, b) M

higher magn

epoxy resince are usualnoindentatiocal calibrat

ration on a astic modulufor polyme

y the observeeen the nanonsile test mea

n Tribology –

d to results ase of softer,ed epoxy r

of typical fracMWCNT, c) Mnification

n material, pilly observedon. It is evideation proced

reference mus such as fuer materialed differencoindentationasurements.

Serbiatrib’13

which are viscoelastic

resin in the

cture surfaces MWCNT at

ile-ups and ad around theent thereforedure which

material of aused silica isls. This isces in elastic

results and

e c e

a e e h a s s c d

13th Internati

Figure 6. Lopure epo

Figure 7.

Neverthemeasured bySubsequentl11] a materbeen utilizeequations (1modified arwas obtainetest of the puthe new calithe nanocomelastic modumarked as modified elain good agreuniaxial tenthe elastic mboth the tenexperiments

Fig. 7 nanocomposconcentratiooutcomes thtrend and inconcentratioshould be n

ional Conferen

oading and unoxy resin and M

. Hardness verMWCNT n

eless the ey both technily as suggestrial dependined for the cu-6) from the

rea function d using the eure epoxy resibrated area fmposites wasulus based on

modified nastic moduluseement with sile tests. Fomodulus is insile tests ans with the pro

also showsites as

on. In agrehe hardness ncreases in thon increases noted that wh

nce on Tribolo

nloadin versusMWCNT nan

rsus of pure epnanocomposite

elastic moduiques revealeted by other ng calibrationurrent measuOliver and Prelated to in

elastic modulusin which wafunction the es calculated. Tn the modifiednanoindentatios values showthe elastic m

or MWCNTs increasing asnd from the

oposed calibraws the ha

a functieement withfollows the he case of Mfrom 0.5%w

hen measured

ogy – Serbiatr

s depth profilenocomposites.

poxy resin andes.

ulus results ed similar tre

researchers n procedure urements. U

Pharr [12, 15],ndentation deus from a tens 3.3 GPa. Uelastic modulThe result ofd area functioon. Clearly, wn in Table 1modulus from

nanocomposs measured f

nanoindentaation techniquardness of ion MWCh the prev

elastic moduMWCNTs aswt to 1%wt

d at small sca

rib’13

es of

d

as ends. [10, has

Using , the epth nsile

Using uli of f the on is

the 1 are

m the sites from ation ue.

the CNT vious dulus s the t. It ales,

the exa‘indincr[16matsmaobtobtepo

is hthispre

5.

nannanmeadvbeeconamdispwitcritandordnan

fibrworMWadonanHalitemomaorieHaof the

hardness iample of thdentation sizerease in hardn

6]. This effectterial hardnesall remainintained in thtained from oxy nanocomThe hardnes

higher than ts explains tsented results ELASTIC M Despite the

notubes, thenofillers exhichanical perf

vanced comexplained byntribution of ount within persion, orienthin the matrticalrole on td they shouldder todevelopnocomposite eThe classicalre reinforcedrk in order

WCNT nanoopted model nocompositeslpin–Tsai m

erature referedel and empcroscopic comented MWClpin–Tsai mthe nanocom following se

58

s larger thahis phenomee effect’ whicness with dect complicatesss at low indeg impression

he current sother studiesposites [17, 1s of the carbthe one fromthe small is.

MODULUS P

outstanding e nanocompibit a very formances,if c

mposites.This y considerinMWCNTs isthe material,ntation,shaperix system. Athe final reind be taken inp reliable meffective propl micromecha

d compositestodevelop pr

ocomposites.Ato predict th

s is the model [19] isences.It is bpirical data amposites.ForCNTs in thodel may prmposites, EN

et of equation

3811

1 21

an at largerenon is thech can be obcreasing indes the determientation deptn. However,study lie ws investigatin18]. bon nanotube

m the epoxy rincrease not

PREDICTIO

mechanical pposites involimited impcompared to

opposingbeng that the s yieldednot , but also bye and numbeAll these feanforcement ento account imodels for pperties. anics approacs were emplpredictive moA popular he stiffness oHalpin-Tsaims widely us

based on a fand it isusedr the moduli the epoxy redictthe elasNC,which is gns:

1

369

r scales. Ane so calledbserved as anntation depthination of theths, given the, the results

within valuesng MWCNT

es themselvesresin therebyticed in the

ONS

properties ofolving suchrovement ofconventionalehavior can

reinforcingonly by their

y the state ofr of contactsatures play aenhancement,if possible inprediction of

ches for shortoyed in this

odels for theand widely

of MWCNTsmodel. Thesed in manyforce balanced widely forof randomlymatrix, the

stic modulusgoverned by

(7)

(8)

9

n d n h e e s s T

s y e

f h f l n g r f s a ,

n f

t s e y s e y e r y e s y

370

Where EMW

the MWCNand l/d are MWCNTs rthat ENC strMWCNTs sthe fibres diametersweΕMWCNT= 1Em=3.3GPa fraction of shown in Fiformula for ENC compananoindenta

Figure 8.M

Figure 9. nanoinde

2

WCNT and Em aNTs and matri

the volume respectively.rongly depensuch as theirranges fro

ere measured1GPa whichthe predicte

the nanotubeig. 9.It can bd=5nm give

ared to the ation using th

MeasurementsMW

Comparison oentation result

Thostenson

1

2

are the Younix respectivefraction and From Eq. 7nds on the gr aspect ratio

om 1-25μm d as seen in Fh is muched values veres of ENC babe seen that es a slight di

ones meashe calibration

s of the outer WCNTs.

of the experimts with the Han-Chou mode

(

ng’s modulusely while vMW

d aspect ratio7 it can be sgeometry of o. The length

while variFigure 8. Takh greater trsus the volu

ased on Eq. the Halpin–Tfferent valuesured from n procedure.

diameter of th

mental modifiealpin-Tsai andls.

13th I

(9)

(10)

s for WCNT o of seen f the h of ious king than ume 7 is Tsai e for

the

he

ed d

Tsareinconoutassinneffeby thegrat=0calcomandcomshodiacommo

thenanAcexpbeobtvoithemixresmevisthemathefrac

thetowtherepconincAlsnanmisdat

nternational C

Thostenson ai theory tonforced comnsidered thater shell wumption of

ner layers. Afective MWC

consideringe outer craphite layer0.34nm). Eqculate the mposite withd impregnatmputed by ow a reducameters whimpared wellodulus for 1%

This occurse SEM invenotube conccounting foperimentally

interpretedtainable moids developee MWCNT/xing and trained thechanical pcosity disab

e nanocompoatrix.The iniese voids ancture strain It is clear t

e models usewards the pre nanocompopresent thevntent, morpcorporating aso, and monotubes agsleading whta.

Conference on

and Chou [wards its apmposites. Tt, in the cas

would carryf the relativAccording tCNT elasticm the applicaosssection r thicknessq. 11 has b

maximumoh aperfect dition within

using Thced level oile for d=3l with the e%wt (0.56%vs despite thestigations thcentrations or any errory derivedvald as a lowduli.Additio

ed during mi/epoxy-suspmechanical

e composierformance

bled a fully osite with vitial failurend expressedin the tensiltherefore thaed in this wrediction of osites they darious issue

phology ana variety of

ost importanglomerated-hen compar

n Tribology –

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ation of all lo(outer dia

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13th International Conference on Tribology – Serbiatrib’13 371

38

1 24

2

14

2

(11)

6. CONCLUSION

The nanoindentation technique has been

successfully utilised in order to study the mechanical properties (i.e. hardness and elastic modulus) of MWCNT/epoxy nanocomposites. The indentation results revealed that the hardness and modulus of the nanocomposites increase with higher MWCNT concentrations. The elastic modulus data obtained by nanoindentation are comparable with those obtained by tensile testing when a suitable material calibration is applied. The results verify the capability of the nanointendation instrumented technique to characterize the mechanical properties of polymer nanocomposites using small sample amounts. Elastic modulus predictions using the Halpin-Tsai model have shown comparable results with the experimental data, while the Thorsten and Chou model provided good predictions by taking into account the outer layer of the nanotubes.

REFERENCES

[1] S. Iijima, Helical microtubules of graphitic carbon Nature, Vol. 354, pp. 56-58, 1991.

[2] K. Sharma, M. Shukla, Experimental study of mechanical properties of multiscale carbon fiber-epoxy-CNT composites, Advanced Materials Research, Vol. 383-390, pp. 2723-2727, 2012.

[3] H.U. Zaman,P.D. Hun, R.A. Khan, K.B. Yoon, Effect of Multi-walled Carbon Nanotubes on Morphology, Mechanical and Thermal Properties of Poly(ethylene Terephthalate) Nanocomposites, Journal of Applied Polymer Science, Vol. 128, No. 4, pp. 2433-2438, 2013.

[4] M.R. Loos, S.H. Pezzin, S.C. Amico, C.P. Bergmann, L.A.F. Coelho, The matrix stiffness role on tensile and thermal properties of carbon nanotubes/epoxy composites, J Mater Sci, Vol. 43, pp. 6064–6069, 2008.

[5] J.A. Kim, D.G. Seong, T.J. Kang, J.R. Youn,Effects of Surface Modification on Rheological and Mechanical Properties of CNT/Epoxy Composites, Carbon, Vol. 44, pp. 1898–1905, 2006.

[6] F.H. Gojny, M.H.G. Wichmann,B. Fiedler, K. Schulte, Influence of nano-reinforcement on the mechanical and electrical properties of conventional fibre reinforced composites, Composites Science and Technology, Vol. 65, pp. 2300–2313, 2005.

[7] P.M. Nagy, D.Aranyi, P.Horváth, P.Pötschke, S. Pegel,E.Kálmán, Nanoindentation Investigation of Carbon Nanotube–Polymer Composites, Internet Electron. J. Mol. Des., Vol. 5, pp. 135–143, 2006.

[8] A.K. Dutta, D. Penumadu, B. Files, Nanoindentation testing for evaluating modulus andhardness of single-walled carbon nanotubereinforced epoxy composites, J. Mater. Res., Vol. 19, pp. 158–64, 2004.

[9] M.R. VanLandingham,Review of instrumented indentation, J. Res. Natl. Inst. Stand. Technol., Vol. 108, pp. 249-265, 2003.

[10] B. J. Briscoey, L.Fiori, E.Pelillo, Nano-indentation of polymeric surfaces, J. Phys. D: Appl. Phys., Vol. 31, pp. 2395–2405, 1998.

[11] M.R. VanLandingham, J.S.Villarrubia, W.F. Guthrie,G.F. Meyers, Nanoindentation of polymers: An Overview, Macromol. Symp., Vol. 167, pp. 15-43, 2001.

[12] W.C. Oliver, G.M. Pharr, An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, J Mater Res, Vol. 7, pp. 1564–1583, 1992.

[13] A. Montazeri,J. Javadpour, A.Khavandi, A. Tcharkhtchi,A.Mohajeri, Mechanical properties of multi-walled carbon nanotube/epoxy composites, Materials and Design, Vol. 31, pp. 4202–4208, 2010.

[14] M. Sánchez, J. Rams, M. Campo, A. Jiménez-Suárez, A.Ureña, Characterization of carbon nanofiber/epoxy nanocomposites by the nanoindentation technique, Composites: Part B, Vol. 42, pp. 638–644, 2011.

372 13th International Conference on Tribology – Serbiatrib’13

[15] W.C. Oliver, G.M. Pharr, Measurement of Hardness and Elastic Modulus by Instrumented Indentation: Advances in Understanding and Refinements to Methodology, J Mater Res, Vol. 19, No. 1, pp. 3–20, 2004.

[16] C.S. Han, Influence of the molecular structure on indentation size effect in polymers, Materials Science and Engineering A, Vol. 527, No. 3, pp. 619-624, 2010.

[17] Sajjad M., B. Feichtenschlager, S. Pabisch, J. Svehla, T. Koch, S. Seidler, H. Peterlik, G. Kickelbickd, Study of the effect of the concentration, size and surface chemistry of zirconia and silica nanoparticle fillers within an epoxy resin on the

bulk properties of the resulting nanocomposites, PolymInt, Vol. 61, pp. 274–285, 2012.

[18] P.M. Nagy, D. Aranyi, P. Horváth, P. Pötschke, S. Pegel, E. Kálmán, Nanoindentation Investigation of Carbon Nanotube - Polymer Composites,Internet Electronic Journal of Molecular Design, Vol. 5, pp. 135–143, 2006.

[19] J.C. Halpin, J.L.Kardos, The Halpin-Tsai equations: A review,Polym. Eng. Sci., Vol. 16, pp. 344–352, 1976.

[20] E.T. Thostenson, T.W. Chou, On the elastic properties of carbon nanotube-based composites: modeling and characterization, J Phys D: ApplPhys, Vol. 36, pp. 573–82, 2003.