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Wear 271 (2011) 2261– 2268

Contents lists available at ScienceDirect

Wear

jou rna l h om epage: www.elsev ier .com/ locate /wear

ear performance of PEEK–carbon fabric composites with strengthenedber–matrix interface

ohit Sharmaa, Jayashree Bijwea,∗, Peter Mitschangb

Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC), Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, IndiaInstitut für Verbundwerkstoffe GmbH, Verarbeitungstechnik, Erwin-Schrödinger-Str., Geb. 58, 67663 Kaiserslautern, Germany

r t i c l e i n f o

rticle history:eceived 22 September 2010eceived in revised form5 November 2010ccepted 25 November 2010

a b s t r a c t

Powder-prepreg method was used to develop composites with untreated and cold remotenitrogen–oxygen (0.5%) plasma (CRNOP) treated carbon fabric (CF) (67–68 wt%) and poly-ether-ether-ketone (PEEK) followed by the evaluation of physical and mechanical properties. Tribo-evaluation inadhesive wear mode was done by sliding a composite pin against a mild steel disc under various loads. Itwas observed that surface treated fabric composites were excellent in mechanical (tensile, flexural and

eywords:arbon fabric reinforced compositesEEKlasma treatment

ILSS – interlaminar shear strength) and tribological properties. A low coefficient of friction (0.21–0.28)and wear rates (1–12 × 10−15 m3/Nm) were recorded for these composites. An enhanced fiber–matrixadhesion was found to play a key role for improvement in performance properties. Raman spectroscopicand SEM studies on worn composites were done and correlated with the wear performance.

© 2011 Elsevier B.V. All rights reserved.

dhesive wear

. Introduction

Specialty thermoplastic polymers are increasingly being usedor the development of high performance composites because ofheir unique advantages, such as higher specific strength, thermaltability, resistance to fatigue, unlimited shelf life, and possibil-ty of recyclability [1]. Amongst the specialty polymers such asolyetheretherketone (PEEK), polyethersulphone (PES), polyether-

mide (PEI), and poly-phenylenesulphide (PPS), PEEK is known forts excellent combination of thermal stability, chemical (resistanceo solvents) and mechanical properties including resistance to wearnd abrasion [1–3]. However, it is difficult to use PEEK in pris-ine form because of its high friction coefficient (�) and stick-slipehavior [2]. In composite form it is rated as one of the mosterforming tribo-materials. Continuous research efforts are beingade to improve the performance properties of PEEK composites

y exploring new fillers such as nano-fillers and fibers/fabrics [4–7].For efficient stress transfer from the matrix to the fibers, during

ear in a composite; the fiber–matrix adhesion is an importantactor, so as to get preferential wear of fibers (which has highear resistance as compared to matrix). Carbon fibers due to their

uperior thermal and mechanical properties are best suited aseinforcement for specialty polymers. However, its chemical inert-ess and surface smoothness lead to less fiber–matrix adhesion

∗ Corresponding author.E-mail address: jbijwe@gmail.com (J. Bijwe).

043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.wear.2010.11.055

and hence weaker composites. The extent of fiber–matrix adhe-sion can be enhanced by employing various surface treatmentsto the fibers prior to their use for composite development. Effortsare hence continuously being made to enhance their surface reac-tivity towards matrix with newer and more efficient methods,either by surface roughening or by adding reactive chemical groups.Cold remote nitrogen plasma (CRNP) treatment to carbon fibers isknown to improve surface–matrix interaction [8–11]. However, atechnique for treating carbon fabric (CF) with cold remote nitro-gen plasma mixed with 0.5% oxygen (CRNOP) is a very recent oneand has proved successful in enhancing strength properties of var-ious composites based on specialty polymers including PEEK in ourrecent work [10]. Plasma treatment improves fiber–matrix adhe-sion largely by introducing polar groups on the fiber-surface layerthat can form strong fiber–matrix bonding and also roughen thesurface of fibers leading to increase in surface area enabling moremechanical interlocking between the fiber and matrix [10].

A lot is reported on the effectiveness of classical and modifiedplasma treatments for influencing performance properties of com-posites, mainly mechanical [11,12] and sparingly tribological also[13,14]. In case of CRNOP treatment to CF, hardly any literature isavailable about its potential in enhancing tribo-performance exceptour own work in fretting and abrasive wear modes for PEI and PEEKcomposites, respectively [15].

Micro-Raman spectroscopy (MRS) has consolidated itself as aunique tool for the evaluation of physical changes in the graphiticstructure of carbon in carbon-based materials. The technique isclaimed to be useful to quantify the stresses in the fibers embedded

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n the matrix. The positions of Raman allowed bands in the fibersre very sensitive to the level of applied stress/strain. Therefore thetress/strain level in the embedded fibers can be evaluated from theaman band shifts. The measured fiber strain profiles provide an

nsight into the interfacial phenomena such as load transfer mech-nism, interfacial debonding, and localized matrix yielding [16]. Inpite of these facts, this technique is not yet exploited for correlat-ng the extent of wear with the structural changes in carbon fibersn the worn composites except in our recently communicated work

here stresses incurred in the carbon fabric–PEEK composite dur-ng erosion were correlated with the amount of wear [17]. In theresent paper, efforts are made to investigate if any such correlationxists in the case of sliding/adhesive wear also.

In our earlier paper, we have reported on the benefits endowedy the treatment of CRNOP to carbon fabric in case of polyether-

mide (PEI) composite by evaluation in fretting wear situation [15].n the present paper, the potential of CRNOP treatment to CF isxploited using PEEK matrix in case of adhesive wear mode. Though

lot is reported on the tribology of PEEK and its short fiber compos-tes and also on unidirectional carbon fibers, not adequate data arevailable on the adhesive wear of carbon fabric–PEEK composites18–20]. The most obvious reason for the same could be the unsuit-bility of most common technique (solution impregnation method)ecause of the unavailability of suitable solvents for PEEK. Hencehe modified technique of powder prepreging is employed in thisaper. The present paper thus reports on the potential of CRNOPreatment for enhancement in tribo-performance of PEEK–CF com-osites in adhesive wear mode, apart from the investigations on thextent of distortion in CF as a function of stresses incurred duringearing process.

. Experimental

.1. Procurement of materials

PEEK powder (150 XF) was supplied by VICTREX, USA. Thearbon fabric of twill weave (2 × 2) used as a reinforcement wasrocured from Fibre Glast Developments Corporation, USA.

.2. Surface treatment of CF

The facility of cold remote nitrogen–oxygen plasmaCRNO(0.5)P) available at University of Science and Technol-gy Lille, France, was used for surface treatment of chemicallynert CF for 15 min to enhance its reactivity towards matrix andetails are discussed elsewhere [21].

.3. Fabrication of composites

Since PEEK is soluble only in few corrosive solvents, con-entional method of solution impregnation is not applicable foreveloping CF–PEEK composites. Hence in the present work, pow-er prepreg process followed by static compression molding wasdopted. Composites were developed at IVW (Institut für Ver-undwerkstoffe) GmbH, Germany, on static press in which theeating and cooling cycles are employed in the same tool. Prior tohe manufacturing process, the piece of fabric (400 mm × 400 mm)as placed on the bed of known weight of PEEK powder on thelaten followed by placement of an alternate sequence of fabricnd powder. The amount of powder was optimised in such a wayhat the fibers in the matrix could be ≈70 wt% in the final composite.

ourteen such layers were arranged between the heating/coolinglates and molded at the maximum temperature of 380 ◦C for0 min and cooled to 20 ◦C. The operating pressure was maintainedt 0.7 mPa during the entire process.

1 (2011) 2261– 2268

In all, two composites designated as CFU and CFT (C for compos-ite; subscripts F for carbon fabric, U for untreated and T for treatedfabric with CRNOP) were developed and studied.

2.4. Characterization of the composites

2.4.1. Physical characterizationThe physical and mechanical characterizations of the devel-

oped composites were done as per ASTM standards (Table 1). Inphysical characterization, density of composites was determinedas per ASTM D792 method. Since PEEK is insoluble in noncor-rosive solvents, ignition loss method (ASTM 2584-02) was usedto calculate fiber weight fraction in PEEK composites which was68 wt.% (55 vol%). Furthermore, the void contents in compositeswere calculated using ASTM 2734 method, which was in the rangeof 0.56–0.58%.

2.4.2. Mechanical characterizationThe composites were evaluated for mechanical (tensile, flexural

and interlaminar shear strength) properties. Tensile strength, ten-sile modulus, toughness and % strain to failure were calculated asper the specifications of ASTM D638 on Zwick 250 universal testingmachine. For this test, the strain was measured with extensometer;cross head speed during the test was 2 mm/min. To avoid slippageof samples during testing, 2 mm thick aluminum tabs were used togrip the samples from both the sides.

Interlaminar shear strength (ILSS) was evaluated according toASTM D2344 on Lloyd LR-100K machine, span to depth ratio forspecimen was 5:1, crosshead speed of 1 mm/min was maintainedduring testing.

Five samples were tested for each type of test and average of bestthree was taken in to consideration. Table 1 shows the data on thephysical and mechanical properties for virgin PEEK and CF–PEEKcomposites reinforced with untreated (U) CF and CRNOP treated(T) CF.

2.4.3. Adhesive wear studiesStudies were done in multi-pass rotary motion on Universal

Macro Tribometer (UMT-3MT) supplied by CETR, USA. The testswere carried out in the pin-on-disc configuration, on S33HE hightorque rotational motion drive loading with 1–1000 N dimensionalforce sensor with the resolution of 5 mN in multi-pass rotationalmotion. The two dimensional force sensor (up to 1 kN load) wasused to measure the sliding as well as frictional force between atribo-couple. The details of schematic and photograph are shownin Fig. 1.

Prior to the experiment the composite pin(10 mm × 10 mm × 4 mm) was slid against a rough mild steeldisc (Ra – roughness in the range 0.3 �m) for uniform contact.After this the rough disc was replaced with the experimental disc(Ra values in the range of 0.1–0.2 �m). Initial weight of pin wasmeasured after cleaning ultrasonically with acetone followed bydrying. It was slid against a mild steel disc at a constant speed of1 m/s. The total sliding distance of 7.2 km was achieved by slidingthe pin for 2 h. After the experiment, pin was again cleaned in asimilar fashion, dried and weighed on a weighing balance withan accuracy of 0.0001 g. The experiment was repeated for threetimes and the average value of weight loss for two closest valueswas considered for specific wear rate calculations. The coefficientof friction as a function of time during sliding was recorded withthe help of viewer software. The experiment was conducted underdifferent loads till the limiting P (pressure) value was reached. This

was realized when some of the features such as excessive increasein � or specific wear rate, increase in temperature of the disc,abrasion marks on the disc or noise generated during experimentwere observed.

M. Sharma et al. / Wear 271 (2011) 2261– 2268 2263

Table 1Physical and mechanical properties of CF–PEEK composites [10].

Properties/materials PEEKa CFU CFT % increase due to CF(untreated) in PEEK

% benefits due totreatment (comparedto untreated fabric)

Fiber weight (wt%) ASTM 2584-02 – 68.2 67.9 – –Density (g/cm3) ASTM D792 1.3 1.43 1.44 – –Tensile strength (MPa) ASTM D638 100 576 627 476 9Tensile modulus (GPa) ASTM D638 3.7 57 60 1440 5Strain at break (%) ASTM D638 15 1.0 1.1 –93 10Toughness (MPa) ASTM D 638 – 3.0 3.4 – 13Flexural strength (MPa) ASTM D 790 170 622 726 265 17Flexural modulus (GPa) ASTM D790 4.1 51 78 1143 53

and T

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a Supplier’s data (C for composite; subscripts – F for carbon fabric, U – untreated

.4.4. Surface topography studiesSEM (ZEISS, EVO-MA10) was used to study the worn surfaces

f specimens. For the sample preparation, these were gold coatedsing ion sputtering method. The surfaces of fibers prior and afterhe treatment were examined with field emission SEM (ZEISS,upra 55).

.4.5. Raman spectroscopic studiesTo investigate the crystalline structural changes after treatment

nd sliding wear, Ranishaw inVia Raman spectrometer with 514 nmeNe laser was used to record Raman spectra of composites slidnder different loads.

. Results and discussion

Fig. 2 consists of FESEM micrographs showing the topographicetails of carbon fiber before and after CRNOP treatment. Coeffi-ient of friction (�) and specific wear rates (K0) as a function ofncreasing load for composites are plotted in Fig. 3. Topography of

orn surfaces of composite pins is shown in SEM and EDAX micro-raphs (Figs. 4–6). Figs. 7 and 8 show the details of Raman spectraor composite slid under 100 N, 200 N and 450 N load and alsohe correlation between wear and structural disorder parameterID/IG).

Table 1 shows the benefits endowed by CF reinforcement and

RNOP treatment for all mechanical properties of composites. Asiscussed in earlier work [10] inclusion of various groups such ascidic and alcoholic (as supported by XPS) on CF was responsibleor the enhanced adhesion with the matrix. Moreover, as seen in

Fig. 1. Schematic with photogr

46 – 7

– treated).

Fig. 2 (micrographs of field emission scanning electron microscopy– FESEM), increase in fiber roughness due to treatment was alsofound responsible for the enhanced adhesion due to the bettermechanical interlocking between the fiber and matrix.

Fig. 3 indicates that the composite with treated fabric (CFT) per-formed better under all loads. CFT exhibited lower � and K0 ascompared to CFU. It was observed that � of materials was in therange 0.2–0.27 while K0 was in the range 1–4.5 × 10−15 m3/Nm,which can be rated as quite low values. The effect on the � dueto treatment was more visible as compared to the wear resistance(WR) when % decrease is considered. The treatment to fibers ledto enhanced adhesion with the matrix and hence extent of variouswear mechanisms such as fiber–matrix debonding due to thermaland mechanical stresses, micro-cracking, micro-cutting, pulveriza-tion, peeling off and pulling out of fibrous debris from the matrixreduced. SEM analysis as discussed in the subsequent section sup-ports this phenomenon.

The � of composites decreased with the load as per generaltrends observed in the case of polymers and composites [22]. Whensurfaces are smooth as in the case of adhesive wear mode, contactof polymeric material against counter face is predominantly elas-tic. Though frictional force remains proportional to the Ar (real areaof contact), Ar is no longer proportional to the load and increasesdisproportionately with the load. Linear curve fitting of � val-ues in Fig. 3(a) was done and slope of the curve was found to

be −0.79. In case of polymer PMMA [22], slope was observed as−0.33. More negative slope indicates that the extent of increase inAr with load is low as compared to that in the case of neat poly-mer, where visco-elasticity is more prominent. This is anticipated

aph of UMT 3 tribometer.

2264 M. Sharma et al. / Wear 271 (2011) 2261– 2268

Fig. 2. FESEM of carbon fibers (a) for virgin fiber and (b) for fiber treated with mixed plasma (N2 and 0.5% O2).

Fig. 3. Coefficient of friction (a) and specific wear rate (b) as a function of load for CFU and CFT composites (counter face mild steel disc, speed – 1 m/s, sliding duration – 2 h).

Fig. 4. SEM micrographs of the surfaces of CF–PEEK composites worn under 100 N load (treated fabric composites (c) and (d) showed lower wear than untreated one (a) and(b)).

M. Sharma et al. / Wear 271 (2011) 2261– 2268 2265

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ig. 5. SEM micrographs of the surfaces of CF–PEEK composites worn under 400 N lb)).

ince fabric reinforcement results in less pronounced effect of theisco-elasticity of polymer and hence extent of elastic deforma-ion decreases. Fabric reinforced composites indicate more extentf plastic deformation and hence less dependence on the load.

The trends in specific wear rate (K0) as a function of load, on theontrary vary for polymers and fiber reinforced polymers (FRPs).or polymers, K0 decreases with the increase in load because ofore and more beneficial and quicker film transfer on the counter

ace at higher loads. For FPPs, however, wear mechanisms are dif-erent. With increase in load, extent of fiber damage (breakage,

ulverization, removal as debris, peeling off and pulling out of fibersnd debris from matrix, fiber–matrix debonding, etc.) increases dis-roportionately and hence K0 increases with load as seen in theresent case (Fig. 3) which is in tune to the literature trends.

Fig. 6. EDAX map for worn surface of CFT indicating

reated fabric composites (c) and (d) showed lower wear than untreated one (a) and

The limiting load value also was influenced to some extent dueto the treated fabric composite. It was observed that at 450 N, theCFU failed within a very short time due to excessive noise and high� while CFT could work under 450 N though � started increasingindicating limiting load was around 450 N.

3.1. SEM analysis

3.1.1. Wear under lower load (100 N)As seen in micrographs in Fig. 4a–d (worn under 100 N), effect

of the tretement to fibers on wear mechanisms can be seen. Asseen in the case of CFU (micrograph in Fig. 4a) the fiber–mtrix wet-ting is almost unnoticable at some places (marked as 1) while atsome places it is minimal (marked as 2). Oveall, the long fibers are

back transferred Fe from the counter face disc.

2266 M. Sharma et al. / Wear 27

Fig. 7. Raman Spectra for CFT composites slid against mild steel disc under differentloads.

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ig. 8. Correlation between wear rate and structural order parameter for CFT com-osites.

everely broken, pulverized and peeled off. In the case of anotheroaction for CFU (micrograph in Fig. 4b) inspite of light load, sur-ace is severely damaged. Back trasfer of matrix from the disc oneverely broken array of fibers can be seen apart from debondedbers (marked as 1). Peeling off or pulling out of fibers and debris

eaving behind the cavities can be seen at varios places. Such fibrousebris when changes the orientation after getting embedded in theatrix (marked as 2-fiber-tip perpendicular to the sliding plane) is

esponsible for the higher �. On the conterary, treated fabric com-osite worn under 100 N (micrographs in Fig. 4c and d), showed

ess amount of fiber–matrix debonding (since initial bonding wastrong), breakage of fibers supporting lower wear of this composite.s seen in micrograph (Fig. 4d), extent of back transfer of matrix isore. Fibers are well embedded in the matrix and show trends ofear thinning (truncated fiber tips suppoting wear of longitudinalbers parallel to the sliding direction).

.1.2. Wear under higher load (400 N)As seen in the micrographs in Fig. 5a–d, effect of higher load on

he surface damage of the composites resulting in high wear can beeen. The surface of CFU and CFT worn under 400 N when comparedo the surfaces worn under 100 N, influence of increased load on theurface damage can be seen in terms of more fiber–matrix debond-

1 (2011) 2261– 2268

ing due to higher thermal and mechanical stresses which is mainlyresponsible for increased fiber damage and removal of debris fromthe surface leading to higher wear. The difference in the extent ofwear due to the treatment of fabric can be easily correlated withthe topography of the surfaces. Micrographs in Fig. 5a and b are forCFU while Fig. 5c and d are for CFT. A large number of debondedfibers as seen in the micrograph in Fig. 5a resulted in easy break-age. Initial weak fiber–matrix adhesion led to easy pulverizationof fibers. These fibers when not supported by the matrix properlydo not support the load. Instead of wearing preferentially and get-ting wear thinned, these fibers get peeled off from the matrix easilyand succumb to easy breakage. As seen in the micrograph in Fig. 5bfor CFU (400 N) the crossover point in the weave (which is weakestpart in the composite because fiber–matrix wetting is minimal) canbe seen. Some fibers have shown indication of wear thinning to asmall extent (marked as1). However, the most prominent featuresof this composite which showed highest wear were: broken fibersseparated from the array after disorientation; large fiber–matrixde-bonding (marked as 2); excessive fiber breakage and removalas fibrous debris (marked as 3) and small amount of back-transferfrom the disc (marked as 4).

In the case of treated fabric composites interesting features wereobserved which were claimed for its low wear (micrographs inFig. 5c and d). Both the surfaces show the cross-over points at dif-ferent loacations. The most prominent feature is the array of fibersstanding proudly in the fabric composite withot any displacement.The stronger initial fiber–matrix bonding is responsible for keepingthe fibers intact together under such harsh operating conditions.Another prominent feature is wear thinning of fibers resulting intruncated ends (marked as 1) which after continuous stresses getso much wear thinned that they get cut easily after very long slid-ing time. All these fibers were wear thinned longitutinally which isthe main cause for low wear of this composite. Various processes offiber damage such as fiber cracking, followed by micro-cutting andpulverization leading to disorientation of wear debris are marked inboth the surfaces as 2. Overall, it was concluded that the fibers couldwear preferentailly because of stronger-fiber–matrix bonding asaresult of CRNOP tretament resulting in high wear resistance.

As seen in micrograph in Fig. 6 (Fe mapping by EDAX), the weardebris of iron particles generated from the wearing of disc getstransferred and embedded on the composite surface. The metallicwear debris (Fe particles) generated during wear of disc gets backtransferred on to the composites surface. These get embedded pref-erentially in the softened matrix due to frictional heat generationand can be easily identified at places where matrix (red colour).Carbon fibers being hard dot allow embedment on their surfaces(black and dark red colour).

3.2. Micro-Raman spectroscopic (MRS) studies

Fig. 7 shows the Raman spectra for CFT slid under 100 N, 200 Nand 450 N load. The bands at 1360 and 1590 cm−1 are the main fea-tures of carbonaceous materials and are called D bands (disordered)and G bands (graphitic), respectively. The degree of structural dis-order of the carbon fibers embedded in the surface of compositeis characterized by the ratio of integrated intensity of disorderinduced (ID) to graphitic band (IG). For FRPs, especially based onthermoplastics there is a huge intensity difference between theRaman peaks for reinforcement and the matrix materials [23].Hence in the present case, the Raman spectra of the carbon fibersembedded in the sliding surface of composites were recorded.

Micro-Raman spectroscopy (MRS) is used in the present case

to study the stresses induced on the fiber surfaces during slidingunder different loads and also to study the interaction between thepolymers and fibers in the composites. Generally, this interactionis reflected by a peak shift or a peak width change [24]. For carbon

M. Sharma et al. / Wear 27

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Fig. 9. Raman Spectra for CFT composites slid under different loads.

bers the graphitic order band (G-band) is featured at frequency590 cm−1, with the increase in sliding load from 100 N to 450 N, aaman shift was observed from 1595 cm−1 to 1607 cm−1 (Fig. 7).

Fig. 8 includes the ID/IG ratios for CFT composites, it was used toorrelate the structural purity of graphitic materials to the graphiterystal domain size [25,26] and the intensity of the D band is consid-red to be defect dependent. With the increase in load, K0 increasednd ID/IG ratio also increased. Higher stresses lead to increase inhe structural disorder of the fiber outer layers and a substantialestruction of basal planes, creating a large number of edge carbontoms [27]. With the increase in applied load, an increased inten-ity of G-band was observed, which may be due to the distortion inbers at the surfaces of composites slid under higher load increaseduring friction process. Such high distortion may attribute to thetrain produced by shear deformation on the frictional surface [28].

As seen in Fig. 9, linear correlation was observed with wear andtructural disorder parameter. Though the data are too small toeneralize, one can say that in case of carbon fabric composites,ood correlation was observed in the amount of wear and stresseshe fibers undergo during wearing.

In the case of CFU also some studies were done by MRS. Inter-stingly, the second order Raman shifts (2D) at frequency range500–3000 cm−1 were observed from the spectra of embeddedbers in the worn CFU, which were not observed for fresh carbonbers [10]. With the increase in sliding load, the 2D peak becomesore pronounced (Fig. 9). This second order disorder band is typi-

ally observed in the case of graphite based materials due to doubleesonance effect; elastic phonon scattering is responsible for theppearance of the D band (disorder band) in the presence of latticeefects and is substituted by an inelastic phonon emission pro-ess for 2D [25]. Thus with the increase in load inelastic phononmission process may also be increased.

. Conclusions

Carbon fabric was treated with cold remote nitrogen–oxygen0.5%) plasma (CRNOP) to explore the possibility of improv-ng fiber–matrix interface and hence mechanical and tribologicalroperties. The composites with PEEK based on similar amountf treated and untreated fabric were developed with the pow-

er prepreg technique. Treated composite exhibited significantlynhanced mechanical properties due to enhanced fiber–matrixdhesion and effectively improved the mechanical (10–15%) anddhesive wear properties of the composites (22–25%). It was con-

[

1 (2011) 2261– 2268 2267

cluded that the low � (≈0.2) and low wear rate (≈1 × 10−15 m3/Nm)exhibited by the CRNOP treated composite was due to the improvedfiber–matrix adhesion as a result of inclusion of chemical groupsand increase in the roughness of fiber. Improved fiber–matrix inter-face led to minimizing the severity of wear-events such as fiberpeeling off from the matrix and hence less damage and hencelower wear and �. Based on the Micro-Raman spectroscopic (MRS)studies on the worn surfaces of composite, a good correlationemerged with the strain produced in the fibers as a result of stressesgenerated during sliding under different loads. At high appliedloads, higher were the accumulated stresses and more strains areproduced on the fibers and hence lesser the wear resistance ofcomposites. Such findings can form a basis of new wear-propertycorrelation studies in the carbon fiber reinforced composites.

Acknowledgements

Authors are grateful to the Council of Scientific and IndustrialResearch (CSIR), New Delhi, India, for funding the work reportedin this paper. Authors are grateful to Prof. Brigitte Mutel from Uni-versity of Lille, France, for extending facility of plasma treatment tothe fabric.

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