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Polyetherimide composites with gamma irradiated carbon fabric: Studies on abrasive wear
Wear 270 (2011) 688–694
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Wear journal homepage: www.elsevier.com/locate/wear
Polyetherimide composites with gamma irradiated carbon fabric: Studies on abrasive wear Sudhir Tiwari a , J. Bijwe a,∗ , S. Panier b a b
Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC), Indian Institute of Technology, Delhi, New Delhi 110016, India Polymers and Composites Technology and Mechanical Engineering Department, Ecole des Mines de Douai, Douai Cedex 59508, France
a r t i c l e
i n f o
Article history: Received 8 October 2010 Received in revised form 22 January 2011 Accepted 28 January 2011 Available online 4 February 2011 Keywords: Carbon fabric Polymer matrix composites Abrasive wear Electron microscopy
a b s t r a c t Interfacial adhesion between matrix and fiber is an important aspect in controlling performance properties of the composites. Carbon fibers are known for chemical inertness and hence limited wettability with the matrix and need prior surface treatment to improve its adhesion with the matrix. In this work, ␥ (gamma) irradiation technique with varying doses (0–300 kGy) was employed to the twill weave carbon fabric (CF) to develop composites with polyetherimide (PEI) matrix based on impregnation method followed by compression molding. Composites were characterized for interlaminar shear strength (ILSS) and abrasive wear performance. Improvement in the friction and wear properties was correlated with the improvement in ILSS as a result of CF treatment. Higher the treatment dose, higher was the ILSS and better was the tribo-performance. SEM studies on fibers indicated increased roughness of the surface as a consequence of treatment and dose. Fourier Transform Infrared Spectroscopy in Attenuated Total Reflectance (FTIR-ATR) mode indicated inclusion of functional groups (mainly carbonyl). Both these factors were responsible for enhancing the fiber–matrix interface. Various techniques such as adhesion test, fiber tension test and Raman spectroscopic analysis of CF were also exploited to analyze the influence of ␥ irradiation on CF. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Carbon fiber is very much preferred as reinforcement due to very important properties such as high specific strength in two directions, thermal conductivity, thermal and thermo-oxidative resistance, low expansion coefficient, self lubricity, etc. However, carbon fibers are chemically inert in nature and hence have poor wettability and adsorption with most of the polymer matrices which results in weak interface. The interface between fiber and matrix is an important aspect in controlling the overall properties of the composite. A strong interface increases the structural stability of the composites and transfers the stress efficiently from matrix to fiber. For enhancing fiber–matrix interfacial adhesion chemical bonding and mechanical interlocking are the most effective ways. Various surface treatment methods such as chemical, electrochemical, thermal, cold plasma, rare earth solution, radiation, etc. have been employed so far to improve the adhesion between the carbon fibers and various matrices [1–7]. Amongst these ␥ irradiation is a very effective approach of tailoring the surface properties of fibers, composites and polymers [7–12]. Radiation affects the crys-
∗ Corresponding author. Tel.: +91 11 26591280; fax: +91 11 26591280. E-mail address: [email protected] (J. Bijwe). 0043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2011.01.035
tal lattice by displacement of atoms within the lattice or electronic excitation. The electrons stripped from the atoms are believed to cause dimensional (topographical) changes in carbon fibers and to create active sites on fiber surfaces which may bind with functional groups of bulk polymers [8]. Moreover, irradiation changes the interfacial microstructure to improve the fiber–matrix interfacial bonding. Surface roughening and polar functionality are the factors which contribute to the interfacial adhesion in ␥-irradiated fibers. Li et al. [7] reported that ␥ treatment enhanced the ILSS of CF/epoxy composites significantly. Wan et al. [8] concluded that the composites with the ␥ irradiated carbon fibers exhibited higher flexural and shear strength than the composites with the airoxidized and untreated fibers. The stronger fiber–matrix bonding was most likely due to the larger amount of the carboxyl group on the surface of the ␥-irradiated fibers. Hassan et al. [9] observed that the ␥-irradiation affects the mechanical and thermal parameters and extent varies from fiber to fiber. The results showed that the irradiation of CF-poly(propylene) composite increased its thermal stability and its tensile strength. In case of CF–Epoxy composites, the ILSS increased with the increase in the dose in the range of 0–250 kGy. The specific surface area of CF and hence contact area between the CF and resin increased. These all factors promoted the formation of a good interface while fabricating composites [10].
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In case of tribology, no paper could be available reporting about the influence of ␥ radiation on carbon fibers followed by development and performance evaluation of composites. Few papers [13] pertain to the similar aspects by reporting influence of ␥ radiation on the composite (and not the fibers) and report increase in abrasive wear resistance of composite of vinylester and glass fibers due to increase in extent of cross-linking of a thermoset polymer. Abrasive wear is the most severe form of wear and is observed in various applications like conveyor aids, vanes, gears, bushes, seals, bearings, pumps handling industrial fluids/slurries containing abrasives, chute liners used in machineries in agriculture, earth moving, mining, etc. [14,15]. In this paper this was selected as a performance evaluation test to explore the potential of ␥ irradiation technique for carbon fibers by developing the composites with polyetherimide (PEI) specialty polymer. 2. Experimental Polyetherimide (PEI) granules (trade name-ULTEM 1000) were supplied by GE plastics, while twill weave (2 × 2) carbon fabric (CF) used as reinforcement was supplied by Fiber Glast Corporation, USA. The treatment to fabric was done by exposing it to Cobalt-60 ␥-radiation source with activity of 1.3 × 104 Curie for three doses (100, 200 and 300 kGy) at the rate of 4.54 kGy/h in air. Carbon fabric was cleaned by boiling in petroleum ether for half an hour. 2.1. Surface analysis Treated and virgin fabrics were analysed with various techniques as follows to investigate the chemical and mechanical changes on the surfaces. 2.1.1. SEM studies SEM studies on untreated and ␥-treated fibers were done after gold coating on Zeiss EVO MA10 microscope to characterize the topographical changes on the fiber surface. 2.1.2. FTIR-ATR analysis In order to investigate the possible changes in the chemical composition of carbon fibers by ␥ treatment, FTIR-ATR analysis was done on the Perkin Elmer SPECTRUM BX FTIR instrument in mid infrared range (4000–700 cm−1 ). 2.1.3. Raman spectroscopy of fibers Raman spectra of untreated and treated CF were obtained on Ranishaw inVia Raman spectroscope with 514 nm He–Ne laser source. The fibers were fixed on a microscope glass slide. The intensity ratio between the D-line (1360 cm−1 ) and G-line (1590 cm−1 ) of the Raman spectra was employed to evaluate the size of the crystalline surface of the carbon fiber samples. Before analysis fibers were cleaned ultrasonically. 2.1.4. Fiber–matrix adhesion studies The effect of ␥ treatment on the improvement in the adhesion between the matrix and CF was analysed by fiber–matrix adhesion test. In this method, small pieces of fabric (100 mm × 100 mm) {virgin and ␥ treated} were accurately weighted and then dipped simultaneously in PEI solution for 3 min and then carefully taken away from the solution and allowed to drip in identical conditions followed by complete drying and weighing. % Gain in weight of the fabric was calculated expecting that the treated fabric would show higher pick-up of matrix. Each fabric was tested for two times and average value was taken for analysis.
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2.1.5. Fiber tow tension test Since the fibers are expected to get surface damaged due to treatment, their strength is likely to get reduced depending on selected treatment. Untreated and ␥ treated CF tows were tested in tension to see the effect of the treatment on tensile strength. A tow (3 K) of fabric was glued on the abrasive paper at a distance of 150 mm. Before starting the tension test, paper was cut from the middle portion to allow the load to come on the tow only. The test was performed on Zwick 250 Universal Testing Machine. Testing speed was 0.5 mm/s. Maximum force taken by the fabric tow was observed. Ten specimens were tested for each fabric sample. Maximum 10% standard deviation was considered. 2.2. Development of composites Composites were developed from PEI (density 1.27 g/cm3 ) based on the impregnation method followed by compression molding. Four types of CF viz. virgin (F0 ), ␥-treated with 100 kGy (FG1 ), 200 kGy (FG2 ) and 300 kGy (FG3 ) doses were used to develop composites. The composites were designated as C0 , CG1 and CG2 and CG3 , respectively. The CF (treated/untreated) roll was cut in pieces of size of 80 mm × 80 mm. The open strands from all the four sides of pieces were sealed with a PTFE coated glass fabric tape to avoid the fiber misalignment. These pieces were immersed in a container (fitted with stacks of perforated trays) filled with viscous solution of PEI (prepared in Dichloromethane) with a density of 1.33. The container was properly sealed to avoid evaporation of solvent, which was required for adequate wetting of fiber strands with the PEI solution. After 12 h, the plies were taken out carefully to avoid misalignment in the weave and dried in oven for 2 h. These 20 prepregs were used to attain the desired thickness (in the range of 3.5–4 mm) and were stacked in the mould carefully. PTFE coated glass fabric was placed on the top and bottom of the stacked prepregs as mould releasing agent. During compression molding, the mould was heated to attain the temperature in the range of 385–390 ◦ C within 2 h. The prepregs were then compression molded at this temperature at an applied pressure of 7.35 MPa. During the total compression time of 20 min at high temperature four intermittent breathings (each of 2 s) were applied to expel residual solvent, if any. The composites were allowed to cool under ambient conditions under applied pressure. The test specimens were cut from the composites with the help of diamond cutter as per required standards for mechanical and tribological testing. In all composites amount of resin was managed to be in the close range by using same density of PEI solution and same processing parameters. 2.3. Characterization of composites 2.3.1. Physical and mechanical properties The composites were characterized for physical and mechanical properties. Density of the composites was determined as per ASTM D792 standards. The composites were evaluated for interlaminar shear strength (ILSS) as per ASTM D2344 standards. The span to thickness ration was 5:1. Tests were performed on Zwick 250 Universal testing machine. 2.4. Abrasive wear studies Abrasive wear studies in a single-pass condition and forward linear motion were conducted on a Linear Abrasive Wear rig fabricated by Magnum Engineers, Bangalore (India) and discussed elsewhere [16]. Prior to the experiment, the composite specimen (10 mm × 10 mm × 3.5–4 mm) was abraded against a fine abrasive paper of grade 800 for uniform contact. Initial weight of such
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Fig. 1. SEM (10kX) of untreated and ␥ treated (100–300 kGy) CF.
ready specimen was measured after cleaning ultrasonically with acetone followed by drying. For abrasive wear study, the specimen was abraded against a waterproof SiC abrasive paper of 120 grade (grit size ≈118 m) fixed on a movable bed at a constant speed (2 m/min). The total sliding distance of 1.5 m was achieved by abrading the specimen in six tracks where each track measured 0.25 m. Experiments was conducted under different loads (10, 20, 30 and 40 N). After the experiment specimen was again cleaned in a similar fashion, dried, and weighed on a weighing balance with an accuracy of 0.0001 g to obtain the final weight of a sample. In all, three experiments were done and average value of weight loss (difference in weight) for two closes values was used for specific wear rate calculations. The specific wear rate (K0 ) was calculated from the following equation; K0 =
m (m3 /N-m) Ld
Table 1 ID /IG ratio and La of untreated and ␥-treated CF. Fiber type
ID /IG
La (Å)
F0 FG1 FG2 FG3
2.92 3.24 3.51 3.95
15.07 13.58 12.54 11.14
and mechanical properties of the composites. Specific wear rates (K0 ) and friction coefficient () of the composites as a function of load are plotted in Figs. 3 and 4, respectively. Fig. 5(a–h) shows SEM micrographs of worn surfaces of composites at 10 and 40 N loads. A schematic diagram of fiber tow tension test is shown in Fig. 6. 3.1. SEM analysis
(1)
where m is the weight loss in kg, is the density of composite in kg/m3 , L is the load in Newton and d the distance abraded in meters. The fabric was always parallel to the abrading plane and warp fibers were parallel to the sliding direction. 3. Results and discussion Fig. 1 shows the SEM micrographs (10kX) of untreated and ␥ treated fibers. FTIR-ATR spectra of untreated and ␥ treated CF is shown in Fig. 2. Table 1 shows (ID /IG ) ratio and surface crystalline size (La) of the carbon fibers. Table 2 gives tensile load taken by the untreated and ␥ treated fabrics tow in tension test and percentage weight gain in adhesion test. Table 3 shows the data on physical
As seen from Fig. 1 surface of the fiber after ␥ treatment was rougher than that of virgin fibers. Smooth surface of untreated fiber was replaced with deep and more closely spaced grooves on the treated fibers, which increases the surface roughness. Increase in roughness was observed with increase in treatment dose. Increased Table 2 Maximum tensile load taken by the untreated and ␥ treated fabric tows in tension test and % weight gain in adhesion test. Type of fiber
Tensile load (N) taken by CF tow
% Wt. gain by CF in adhesion test
F0 FG1 FG2 FG3
246 230 217 202
51.96 56.79 61.07 63.83
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Fig. 2. FTIR-ATR spectra of untreated and ␥ treated CF.
roughness gives increase in surface area and more number of sites for mechanical interlocking between fiber and matrix. This was one of the causes which led to enhanced fiber–matrix adhesion as discussed in Section 3.4.
as these groups are helpful in increasing chemical activity of fabric surface.
3.2. FTIR-ATR analysis
The bands with intensity 1360 cm−1 and 1593 cm−1 are the main features of carbon materials and are called D bands (disordered) and G bands (graphitic), respectively. The degree of structural disorder of the fibers was characterized by ratio of curve areas of integrated intensity of disorder induced (ID ) to Raman allowed band (IG ). Lorentzian functions were used to obtain the intensity (ID /IG ) ratio and the respective surface crystalline size (La) of the carbon fibers from Raman spectra. The crystalline size was obtained by the following the relationship [17]:
As seen in Fig. 2, FTIR-ATR spectrum of untreated fibers did not show any absorption peaks while that of ␥ treated fibers showed presence of oxygenated polar functional groups such as ether and carbonyl corresponding to wave number range of 900–1250 cm−1 , 1500–1650 cm−1 , respectively. The prominent IR peaks for ether group for FG1 , FG2 and FG3 was obtained at 1017, 1022, 1037 cm−1 and 1213, 1211, 1214 cm−1 , respectively, and carbonyl group at 1577, 1593 and 1596 cm−1 , respectively. The area of the peaks indicating quantitative amount of groups, increased sharply beyond 100 kGy dose. The presence of functional groups could be another cause for improvement in the adhesion between matrix and fabric
3.3. Raman spectroscopic analysis of fibers
La =
C (ID /IG )
(2)
˚ where La is the surface crystalline size and C is equal to 44 A.
Table 3 Physical and mechanical properties of composites. Composites
Fiber wt. (%)
Fiber vol. (%)
Void vol. (%)
Density (g/cm3 )
ILSS (MPa)
C0 CG1 CG2 CG3
67.15 66.70 67.47 68.3
55.53 55.16 55.80 56.49
0.48 0.51 0.51 0.5
1.54 1.55 1.56 1.56
34 44 51 54
± ± ± ±
1.7 2.2 1.42 1.35
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tion in strength and higher was the matrix pick up. This reduction may be due to the increment in pits and grooves on the surface after treatment. The increase in adhesion due to roughening of fiber surface is always at the cost of the strength. Thus the net strength of the composite containing such fibrous reinforcement depends on the contribution of these two processes acting in opposite directions (Fig. 6). 3.6. Studies on composites 3.6.1. Physical and mechanical properties As seen in Table 3, vol.% of CF in the composites was in the range of 55–56%, while % void contents were around 0.5%. As seen in Table 3, with increase in the dose from 0 to 300 kGy, continuous increase in the ILSS was observed. After rapid increase initially up to 200 kGy, it slowed down for 300 kGy. For this dose, ≈60% improvement in the ILSS of composite was observed. This indicates significant enhancement in the adhesion of CF and matrix after treatment. Fig. 3. Specific wear rates of composites under selected loads.
Table 1 shows that the ␥ treatment led to a rise in the ID /IG ratio which indicates an increase in the degree of disorder which may be due to slight distortion in graphitic structure of CF which would occur through the breaking of bonds and the reduction in surface crystallinity [17]. 3.4. Fiber–matrix adhesion As seen in Table 2, weight gained by the ␥ treated fabric was more than the untreated one in fiber–matrix adhesion test and was in the order; FG3 > FG2 > FG1 > F0 This enhanced weight gain in treated fabric may be attributed to the improved adhesion of the matrix with the fabric, which was caused by the changes in topography and inclusion of some oxygenated functional groups on CF after ␥ treatment as indicated by SEM and FTIR-ATR analysis in the previous sections. 3.5. Fiber tow tension test As seen in Table 2 treated fibers showed lower tensile strength as compared to the untreated one. Higher the dose, higher was the roughness and pitting on the surface of fibers, higher was the reduc-
Fig. 4. Coefficient of friction of composites under selected loads.
3.6.2. Abrasive wear study As seen in Fig. 3, the specific wear rates (K0 ) for all the composites were in the range of (5–10) × 10−10 m3 /Nm and following was the order of K0 for all loads C0 > CG1 > CG2 > CG3 Almost 40% and 20% decrease in wear rate and approximately 20% in was observed due to 300 kGy dose when composites were abraded under 10 and 40 N, respectively. of composites was in the range 0.4–0.6 and the magnitude followed the same trends confirming that the ␥ irradiation treatment proved beneficial to increase the strength properties, wear resistance and to reduce friction coefficient. Higher the dose, higher was the improvement in properties. In the selected range of doses, however, no peak value in properties was observed. Hence the comment on the optimized dose of treatment could not be done. As fiber–matrix adhesion improved, wear of composites decreased since various wear mechanisms such as fiber debonding, micro-cracking, micro-cutting followed by pulverization, peeling off and pulling out of fibrous debris from the matrix also reduced as supported by SEM studies of worn surfaces in subsequent section. As fiber damage decreased, production of wear debris also decreased. During sliding, this debris gets disoriented causing more friction. Higher the wear, higher is the amount of debris and its disorientation and higher is the coefficient of friction. Thus stronger fiber–matrix bonding helps in reducing both, wear and friction in composites. K0 decreased with increase in load which is a general trend for fiber reinforced composites in case of abrasive wear [18–20]. of composites also decreased with load and was in tune to the Lhymn’s equation [21]. 3.6.3. SEM studies of composites Micrographs in Fig. 5(a–h) are arranged in the increasing order of wear performance. Various wear mechanisms which were commonly observed on the surfaces are described in the caption. Micrographs Fig. 5(a), (c), (e) and (g) are for worn surfaces of C0 , CG1 , CG2 and CG3 composites under 10 N while those in Fig. 5(b), (d), (f) and (h) are for 40 N load. When these are compared row wise, influence of increasing load on the topography of a particular composite can be seen. When these are compared column-wise, they show gradual decrease in wear and also in damage of fibers which was responsible for the improved wear performance. Interestingly, increase in fiber–matrix adhesion can also be seen when micrographs are compared column wise. Fiber cracking, cutting, fiber–matrix de-bonding and fiber pullout are the most dominating wear mechanisms along with micro-ploughing of the matrix
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Fig. 5. SEM micrographs (×1000) of surfaces of various composites worn under two extreme loads (a, c, e, and g for 10 N and b, d, f and h for 40 N). Various stages of fiber during shearing action by grit; (1) micro groove formed due to micro cutting of array of fibers; (2) initiation of fiber cracking; (3) fiber cutting; (4) fiber matrix debonding; (5) matrix ploughing; (6) fiber pulverization and (7) fiber pullout.
in these micrographs. Micrograph Fig. 5(a) shows array of fibers (almost naked) in warp and weft direction along with a deep groove ploughed due to abrasion of SiC particle. Fibers in weft direction (perpendicular to sliding direction) show maximum damage and
brittle fracture. Most of the fibers are cut across the diameter. Fibers in warp direction (parallel to sliding direction) showed less damage and different types of fractures. Fiber cracking followed micro-cutting and pulverization are observed phenomena in such
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distortion in the graphitic structure. The enhancement in adhesion between the matrix and CF led to improvement in ILSS of all the composites. Almost 60% increase in ILSS was exhibited by CG3. Overall it was concluded that ␥ treatment to CF proved beneficial for improvement in all the properties including abrasive wear resistance and friction. Highest dose of treatment was most beneficial in these regards. Acknowledgement Authors gratefully acknowledge Dr. P.S. Datta, Principal Scientist, Division of Agriculture Physics, IARI, New Delhi, India for extending ␥-irradiation facility for this work. References Fig. 6. Schematic diagram of fiber tow tension test.
fibers lying in this direction. At various places, these are pulverized and small portions are removed during abrasion as wear debris. The drastic difference in the worn surfaces of composites with untreated and treated fabrics is apparent in the form of amount of resin adhering and protecting the fibers and leading to less and less damage. Micrograph Fig. 5(g) shows so much amount of resin on the surface that very few broken fibers are visible. When fiber–matrix interface is strong, fiber can resist the shearing forces more efficiently and thus resulting in lower wear. Effect of increasing load on the damage of fibers and subsequently resulting in high wear of composites can be seen in Fig. 5, when micrographs Fig. 5(a) and (b); (c) and (d); (e) and (f); and (g) and (h) are compared. Micrographs Fig. 5(b) and (d) show higher depth of grooves due to higher loads revealing multiple layers of fractured fibers. When micrographs Fig. 5(g) and (h) are compared, in spite of high amount of resin protecting fibers, these are still fractured because of higher load. The extents of fiber pull out increase as load increases to 40 N from 10 N. Thus the worn surfaces showed complete correlation with the wear performance and fiber–matrix adhesion. 4. Conclusions Based on the studies on composites developed with PEI matrix and carbon fabric treated with various doses of ␥ rays, it was concluded that the ␥-treatment to CF led to the significant changes in the surface topography of fibers and inclusion of chemical groups such as ether and carbonyl. With increase in dose from 0 to 300 kGy, roughness of the fiber surface increased, as evident from SEM studies and the tensile strength of the fiber decreased. It was also concluded that the ␥ treatment led to the enhancement in the fiber–matrix adhesion as evident from the matrix pick up studies in adhesion test and SEM studies on worn composites. Based on observations in Raman spectroscopic studies (based on ID /IG ratio stresses), it was concluded that stresses induced in the fibers during irradiation (which were direct functions of amount of doses) could be directly correlated with reduction in crystallinity and the
[1] J. Li, F.F. Sun, The effect of nitric acid oxidization treatment on the interface of carbon fiber-reinforced thermoplastic polystyrene composite, Poly. Plast. Tech. Eng. 48 (2009) 701–715. [2] A. Fukunata, S. Ueda, Anodic surface oxidation for pitch-based carbon fibers and the interfacial bond strengths in epoxy matrices, Compos. Sci. Tech. 60 (2000) 249–254. [3] L.Y. Zhang, L.X. Zhao, J.J. Zhang, The effect of fiber oxidation on the tribological behavior of 3D braided carbon fiber/nylon composites, Wear 262 (7–8) (2007) 1026–1030. [4] B.Z. Jang, Control of interfacial adhesion in continuous carbon and Kevlar fiber reinforced polymer composites, Comp. Sci. Technol. 44 (4) (1992) 333–349. [5] M. Sun, B. Hu, Y. Wu, Y. Tang, W. Huang, Y. Da, Surface of carbon fibers continuously treated by cold plasma, Comp. Sci. Technol. 34 (1989) 353–364. [6] Z. Xu, Y. Huang, C. Zhang, L. Chen, Influence of rare earth treatment on interfacial properties of carbon fiber/epoxy composites, Mater. Sci. Eng. A 444 (2007) 170–177. [7] J. Li, Y. Huang, Z. Xu, Z. Wang, High-energy radiation technique treat on the surface of carbon fiber, Mater. Chem. Phys. 94 (2005) 315–321. [8] Y.Z. Wan, Y.L. Wang, Y. Huang, H.L. Luo, G.C. Chen, C.D. Yuan, Effect of surface treatment of carbon fibers with ␥-ray radiation on mechanical performance of their composites, J. Mat. Sci. 40 (2005) 3355–3359. [9] M.M. Hassan, A. El-Hag Ali, G.A. Mahoud, E.A. Hegazy, Synergistic effect of short reinforced fibers and ␥ rays on the thermal and mechanical properties of waste poly(propylene) composites, J. Appl. Polym. Sci. 96 (2005) 1741–1747. [10] J. Li, Y. Huang, S. Fu, L. Yang, H. Qu, G. Wu, Study on the surface performance of carbon fibers irradiated by ␥-ray under different irradiation dose, Appl. Surf. Sci. 256 (2010) 2000–2004. [11] E.N. Hoffman, T.E. Skidmore, Radiation effects on epoxy/carbon–fiber composite, J. Nucl. Mater. 392 (2009) 371–378. [12] J.M. Pintado, J. Miguel, Effect of ␥ irradiation on mechanical behavior of carbon/epoxy composites materials, Cryogenics 38 (1998) 85–89. [13] N. Chand, M. Fahim, Irradiation effects on the abrasive wear of glass fibre–vinylester composites, Tribol. Lett. 3 (1997) 157–160. [14] G.W. Stachowiak, A.W. Batchelor, Engineering Tribology, Elsevier, Amsterdam, 1993. [15] K. Friedrich, Friction and wear of polymer composites, in: K. Friedrich (Ed.), Composite Materials Series 1, Elsevier, Amsterdam, 1986. [16] J. Bijwe, Rekha Rattan, M. Fahim, Abrasive wear performance of carbon fabric reinforced polyetherimide composites: influence of content and orientation of fabric, Tribol. Int. 40 (2007) 844–854. [17] M.J. Matthews, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Origin of dispersive effects of the Raman d band in carbon materials, Phys. Rev. B 59 (10) (1999) 6585–6588. [18] R. Rattan, J. Bijwe, Influence of weave of carbon fabric on abrasive wear performance of polyetherimide composites, Tribol. Lett. 22 (1) (2006) 105–112. [19] J. Bijwe, R. Rattan, M. Fahim, Abrasive wear performance of carbon fabric reinforced polyetherimide composites: influence of content and orientation of fabric, Tribol. Int. 40 (2007) 844–854. [20] J. Bijwe, J. Indumathi, A.K. Ghosh, On the abrasive wear behavior of fabricreinforced polyetherimide composites, Wear 253 (2002) 768–777. [21] C. Lhymn, K.E. Templemeyer, P.K. Davis, The abrasive wear of short fiber composites, Composites 16 (2) (1985) 127–136.
Contents lists available at ScienceDirect
Wear journal homepage: www.elsevier.com/locate/wear
Polyetherimide composites with gamma irradiated carbon fabric: Studies on abrasive wear Sudhir Tiwari a , J. Bijwe a,∗ , S. Panier b a b
Industrial Tribology Machine Dynamics and Maintenance Engineering Centre (ITMMEC), Indian Institute of Technology, Delhi, New Delhi 110016, India Polymers and Composites Technology and Mechanical Engineering Department, Ecole des Mines de Douai, Douai Cedex 59508, France
a r t i c l e
i n f o
Article history: Received 8 October 2010 Received in revised form 22 January 2011 Accepted 28 January 2011 Available online 4 February 2011 Keywords: Carbon fabric Polymer matrix composites Abrasive wear Electron microscopy
a b s t r a c t Interfacial adhesion between matrix and fiber is an important aspect in controlling performance properties of the composites. Carbon fibers are known for chemical inertness and hence limited wettability with the matrix and need prior surface treatment to improve its adhesion with the matrix. In this work, ␥ (gamma) irradiation technique with varying doses (0–300 kGy) was employed to the twill weave carbon fabric (CF) to develop composites with polyetherimide (PEI) matrix based on impregnation method followed by compression molding. Composites were characterized for interlaminar shear strength (ILSS) and abrasive wear performance. Improvement in the friction and wear properties was correlated with the improvement in ILSS as a result of CF treatment. Higher the treatment dose, higher was the ILSS and better was the tribo-performance. SEM studies on fibers indicated increased roughness of the surface as a consequence of treatment and dose. Fourier Transform Infrared Spectroscopy in Attenuated Total Reflectance (FTIR-ATR) mode indicated inclusion of functional groups (mainly carbonyl). Both these factors were responsible for enhancing the fiber–matrix interface. Various techniques such as adhesion test, fiber tension test and Raman spectroscopic analysis of CF were also exploited to analyze the influence of ␥ irradiation on CF. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Carbon fiber is very much preferred as reinforcement due to very important properties such as high specific strength in two directions, thermal conductivity, thermal and thermo-oxidative resistance, low expansion coefficient, self lubricity, etc. However, carbon fibers are chemically inert in nature and hence have poor wettability and adsorption with most of the polymer matrices which results in weak interface. The interface between fiber and matrix is an important aspect in controlling the overall properties of the composite. A strong interface increases the structural stability of the composites and transfers the stress efficiently from matrix to fiber. For enhancing fiber–matrix interfacial adhesion chemical bonding and mechanical interlocking are the most effective ways. Various surface treatment methods such as chemical, electrochemical, thermal, cold plasma, rare earth solution, radiation, etc. have been employed so far to improve the adhesion between the carbon fibers and various matrices [1–7]. Amongst these ␥ irradiation is a very effective approach of tailoring the surface properties of fibers, composites and polymers [7–12]. Radiation affects the crys-
∗ Corresponding author. Tel.: +91 11 26591280; fax: +91 11 26591280. E-mail address: [email protected] (J. Bijwe). 0043-1648/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2011.01.035
tal lattice by displacement of atoms within the lattice or electronic excitation. The electrons stripped from the atoms are believed to cause dimensional (topographical) changes in carbon fibers and to create active sites on fiber surfaces which may bind with functional groups of bulk polymers [8]. Moreover, irradiation changes the interfacial microstructure to improve the fiber–matrix interfacial bonding. Surface roughening and polar functionality are the factors which contribute to the interfacial adhesion in ␥-irradiated fibers. Li et al. [7] reported that ␥ treatment enhanced the ILSS of CF/epoxy composites significantly. Wan et al. [8] concluded that the composites with the ␥ irradiated carbon fibers exhibited higher flexural and shear strength than the composites with the airoxidized and untreated fibers. The stronger fiber–matrix bonding was most likely due to the larger amount of the carboxyl group on the surface of the ␥-irradiated fibers. Hassan et al. [9] observed that the ␥-irradiation affects the mechanical and thermal parameters and extent varies from fiber to fiber. The results showed that the irradiation of CF-poly(propylene) composite increased its thermal stability and its tensile strength. In case of CF–Epoxy composites, the ILSS increased with the increase in the dose in the range of 0–250 kGy. The specific surface area of CF and hence contact area between the CF and resin increased. These all factors promoted the formation of a good interface while fabricating composites [10].
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In case of tribology, no paper could be available reporting about the influence of ␥ radiation on carbon fibers followed by development and performance evaluation of composites. Few papers [13] pertain to the similar aspects by reporting influence of ␥ radiation on the composite (and not the fibers) and report increase in abrasive wear resistance of composite of vinylester and glass fibers due to increase in extent of cross-linking of a thermoset polymer. Abrasive wear is the most severe form of wear and is observed in various applications like conveyor aids, vanes, gears, bushes, seals, bearings, pumps handling industrial fluids/slurries containing abrasives, chute liners used in machineries in agriculture, earth moving, mining, etc. [14,15]. In this paper this was selected as a performance evaluation test to explore the potential of ␥ irradiation technique for carbon fibers by developing the composites with polyetherimide (PEI) specialty polymer. 2. Experimental Polyetherimide (PEI) granules (trade name-ULTEM 1000) were supplied by GE plastics, while twill weave (2 × 2) carbon fabric (CF) used as reinforcement was supplied by Fiber Glast Corporation, USA. The treatment to fabric was done by exposing it to Cobalt-60 ␥-radiation source with activity of 1.3 × 104 Curie for three doses (100, 200 and 300 kGy) at the rate of 4.54 kGy/h in air. Carbon fabric was cleaned by boiling in petroleum ether for half an hour. 2.1. Surface analysis Treated and virgin fabrics were analysed with various techniques as follows to investigate the chemical and mechanical changes on the surfaces. 2.1.1. SEM studies SEM studies on untreated and ␥-treated fibers were done after gold coating on Zeiss EVO MA10 microscope to characterize the topographical changes on the fiber surface. 2.1.2. FTIR-ATR analysis In order to investigate the possible changes in the chemical composition of carbon fibers by ␥ treatment, FTIR-ATR analysis was done on the Perkin Elmer SPECTRUM BX FTIR instrument in mid infrared range (4000–700 cm−1 ). 2.1.3. Raman spectroscopy of fibers Raman spectra of untreated and treated CF were obtained on Ranishaw inVia Raman spectroscope with 514 nm He–Ne laser source. The fibers were fixed on a microscope glass slide. The intensity ratio between the D-line (1360 cm−1 ) and G-line (1590 cm−1 ) of the Raman spectra was employed to evaluate the size of the crystalline surface of the carbon fiber samples. Before analysis fibers were cleaned ultrasonically. 2.1.4. Fiber–matrix adhesion studies The effect of ␥ treatment on the improvement in the adhesion between the matrix and CF was analysed by fiber–matrix adhesion test. In this method, small pieces of fabric (100 mm × 100 mm) {virgin and ␥ treated} were accurately weighted and then dipped simultaneously in PEI solution for 3 min and then carefully taken away from the solution and allowed to drip in identical conditions followed by complete drying and weighing. % Gain in weight of the fabric was calculated expecting that the treated fabric would show higher pick-up of matrix. Each fabric was tested for two times and average value was taken for analysis.
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2.1.5. Fiber tow tension test Since the fibers are expected to get surface damaged due to treatment, their strength is likely to get reduced depending on selected treatment. Untreated and ␥ treated CF tows were tested in tension to see the effect of the treatment on tensile strength. A tow (3 K) of fabric was glued on the abrasive paper at a distance of 150 mm. Before starting the tension test, paper was cut from the middle portion to allow the load to come on the tow only. The test was performed on Zwick 250 Universal Testing Machine. Testing speed was 0.5 mm/s. Maximum force taken by the fabric tow was observed. Ten specimens were tested for each fabric sample. Maximum 10% standard deviation was considered. 2.2. Development of composites Composites were developed from PEI (density 1.27 g/cm3 ) based on the impregnation method followed by compression molding. Four types of CF viz. virgin (F0 ), ␥-treated with 100 kGy (FG1 ), 200 kGy (FG2 ) and 300 kGy (FG3 ) doses were used to develop composites. The composites were designated as C0 , CG1 and CG2 and CG3 , respectively. The CF (treated/untreated) roll was cut in pieces of size of 80 mm × 80 mm. The open strands from all the four sides of pieces were sealed with a PTFE coated glass fabric tape to avoid the fiber misalignment. These pieces were immersed in a container (fitted with stacks of perforated trays) filled with viscous solution of PEI (prepared in Dichloromethane) with a density of 1.33. The container was properly sealed to avoid evaporation of solvent, which was required for adequate wetting of fiber strands with the PEI solution. After 12 h, the plies were taken out carefully to avoid misalignment in the weave and dried in oven for 2 h. These 20 prepregs were used to attain the desired thickness (in the range of 3.5–4 mm) and were stacked in the mould carefully. PTFE coated glass fabric was placed on the top and bottom of the stacked prepregs as mould releasing agent. During compression molding, the mould was heated to attain the temperature in the range of 385–390 ◦ C within 2 h. The prepregs were then compression molded at this temperature at an applied pressure of 7.35 MPa. During the total compression time of 20 min at high temperature four intermittent breathings (each of 2 s) were applied to expel residual solvent, if any. The composites were allowed to cool under ambient conditions under applied pressure. The test specimens were cut from the composites with the help of diamond cutter as per required standards for mechanical and tribological testing. In all composites amount of resin was managed to be in the close range by using same density of PEI solution and same processing parameters. 2.3. Characterization of composites 2.3.1. Physical and mechanical properties The composites were characterized for physical and mechanical properties. Density of the composites was determined as per ASTM D792 standards. The composites were evaluated for interlaminar shear strength (ILSS) as per ASTM D2344 standards. The span to thickness ration was 5:1. Tests were performed on Zwick 250 Universal testing machine. 2.4. Abrasive wear studies Abrasive wear studies in a single-pass condition and forward linear motion were conducted on a Linear Abrasive Wear rig fabricated by Magnum Engineers, Bangalore (India) and discussed elsewhere [16]. Prior to the experiment, the composite specimen (10 mm × 10 mm × 3.5–4 mm) was abraded against a fine abrasive paper of grade 800 for uniform contact. Initial weight of such
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Fig. 1. SEM (10kX) of untreated and ␥ treated (100–300 kGy) CF.
ready specimen was measured after cleaning ultrasonically with acetone followed by drying. For abrasive wear study, the specimen was abraded against a waterproof SiC abrasive paper of 120 grade (grit size ≈118 m) fixed on a movable bed at a constant speed (2 m/min). The total sliding distance of 1.5 m was achieved by abrading the specimen in six tracks where each track measured 0.25 m. Experiments was conducted under different loads (10, 20, 30 and 40 N). After the experiment specimen was again cleaned in a similar fashion, dried, and weighed on a weighing balance with an accuracy of 0.0001 g to obtain the final weight of a sample. In all, three experiments were done and average value of weight loss (difference in weight) for two closes values was used for specific wear rate calculations. The specific wear rate (K0 ) was calculated from the following equation; K0 =
m (m3 /N-m) Ld
Table 1 ID /IG ratio and La of untreated and ␥-treated CF. Fiber type
ID /IG
La (Å)
F0 FG1 FG2 FG3
2.92 3.24 3.51 3.95
15.07 13.58 12.54 11.14
and mechanical properties of the composites. Specific wear rates (K0 ) and friction coefficient () of the composites as a function of load are plotted in Figs. 3 and 4, respectively. Fig. 5(a–h) shows SEM micrographs of worn surfaces of composites at 10 and 40 N loads. A schematic diagram of fiber tow tension test is shown in Fig. 6. 3.1. SEM analysis
(1)
where m is the weight loss in kg, is the density of composite in kg/m3 , L is the load in Newton and d the distance abraded in meters. The fabric was always parallel to the abrading plane and warp fibers were parallel to the sliding direction. 3. Results and discussion Fig. 1 shows the SEM micrographs (10kX) of untreated and ␥ treated fibers. FTIR-ATR spectra of untreated and ␥ treated CF is shown in Fig. 2. Table 1 shows (ID /IG ) ratio and surface crystalline size (La) of the carbon fibers. Table 2 gives tensile load taken by the untreated and ␥ treated fabrics tow in tension test and percentage weight gain in adhesion test. Table 3 shows the data on physical
As seen from Fig. 1 surface of the fiber after ␥ treatment was rougher than that of virgin fibers. Smooth surface of untreated fiber was replaced with deep and more closely spaced grooves on the treated fibers, which increases the surface roughness. Increase in roughness was observed with increase in treatment dose. Increased Table 2 Maximum tensile load taken by the untreated and ␥ treated fabric tows in tension test and % weight gain in adhesion test. Type of fiber
Tensile load (N) taken by CF tow
% Wt. gain by CF in adhesion test
F0 FG1 FG2 FG3
246 230 217 202
51.96 56.79 61.07 63.83
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Fig. 2. FTIR-ATR spectra of untreated and ␥ treated CF.
roughness gives increase in surface area and more number of sites for mechanical interlocking between fiber and matrix. This was one of the causes which led to enhanced fiber–matrix adhesion as discussed in Section 3.4.
as these groups are helpful in increasing chemical activity of fabric surface.
3.2. FTIR-ATR analysis
The bands with intensity 1360 cm−1 and 1593 cm−1 are the main features of carbon materials and are called D bands (disordered) and G bands (graphitic), respectively. The degree of structural disorder of the fibers was characterized by ratio of curve areas of integrated intensity of disorder induced (ID ) to Raman allowed band (IG ). Lorentzian functions were used to obtain the intensity (ID /IG ) ratio and the respective surface crystalline size (La) of the carbon fibers from Raman spectra. The crystalline size was obtained by the following the relationship [17]:
As seen in Fig. 2, FTIR-ATR spectrum of untreated fibers did not show any absorption peaks while that of ␥ treated fibers showed presence of oxygenated polar functional groups such as ether and carbonyl corresponding to wave number range of 900–1250 cm−1 , 1500–1650 cm−1 , respectively. The prominent IR peaks for ether group for FG1 , FG2 and FG3 was obtained at 1017, 1022, 1037 cm−1 and 1213, 1211, 1214 cm−1 , respectively, and carbonyl group at 1577, 1593 and 1596 cm−1 , respectively. The area of the peaks indicating quantitative amount of groups, increased sharply beyond 100 kGy dose. The presence of functional groups could be another cause for improvement in the adhesion between matrix and fabric
3.3. Raman spectroscopic analysis of fibers
La =
C (ID /IG )
(2)
˚ where La is the surface crystalline size and C is equal to 44 A.
Table 3 Physical and mechanical properties of composites. Composites
Fiber wt. (%)
Fiber vol. (%)
Void vol. (%)
Density (g/cm3 )
ILSS (MPa)
C0 CG1 CG2 CG3
67.15 66.70 67.47 68.3
55.53 55.16 55.80 56.49
0.48 0.51 0.51 0.5
1.54 1.55 1.56 1.56
34 44 51 54
± ± ± ±
1.7 2.2 1.42 1.35
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tion in strength and higher was the matrix pick up. This reduction may be due to the increment in pits and grooves on the surface after treatment. The increase in adhesion due to roughening of fiber surface is always at the cost of the strength. Thus the net strength of the composite containing such fibrous reinforcement depends on the contribution of these two processes acting in opposite directions (Fig. 6). 3.6. Studies on composites 3.6.1. Physical and mechanical properties As seen in Table 3, vol.% of CF in the composites was in the range of 55–56%, while % void contents were around 0.5%. As seen in Table 3, with increase in the dose from 0 to 300 kGy, continuous increase in the ILSS was observed. After rapid increase initially up to 200 kGy, it slowed down for 300 kGy. For this dose, ≈60% improvement in the ILSS of composite was observed. This indicates significant enhancement in the adhesion of CF and matrix after treatment. Fig. 3. Specific wear rates of composites under selected loads.
Table 1 shows that the ␥ treatment led to a rise in the ID /IG ratio which indicates an increase in the degree of disorder which may be due to slight distortion in graphitic structure of CF which would occur through the breaking of bonds and the reduction in surface crystallinity [17]. 3.4. Fiber–matrix adhesion As seen in Table 2, weight gained by the ␥ treated fabric was more than the untreated one in fiber–matrix adhesion test and was in the order; FG3 > FG2 > FG1 > F0 This enhanced weight gain in treated fabric may be attributed to the improved adhesion of the matrix with the fabric, which was caused by the changes in topography and inclusion of some oxygenated functional groups on CF after ␥ treatment as indicated by SEM and FTIR-ATR analysis in the previous sections. 3.5. Fiber tow tension test As seen in Table 2 treated fibers showed lower tensile strength as compared to the untreated one. Higher the dose, higher was the roughness and pitting on the surface of fibers, higher was the reduc-
Fig. 4. Coefficient of friction of composites under selected loads.
3.6.2. Abrasive wear study As seen in Fig. 3, the specific wear rates (K0 ) for all the composites were in the range of (5–10) × 10−10 m3 /Nm and following was the order of K0 for all loads C0 > CG1 > CG2 > CG3 Almost 40% and 20% decrease in wear rate and approximately 20% in was observed due to 300 kGy dose when composites were abraded under 10 and 40 N, respectively. of composites was in the range 0.4–0.6 and the magnitude followed the same trends confirming that the ␥ irradiation treatment proved beneficial to increase the strength properties, wear resistance and to reduce friction coefficient. Higher the dose, higher was the improvement in properties. In the selected range of doses, however, no peak value in properties was observed. Hence the comment on the optimized dose of treatment could not be done. As fiber–matrix adhesion improved, wear of composites decreased since various wear mechanisms such as fiber debonding, micro-cracking, micro-cutting followed by pulverization, peeling off and pulling out of fibrous debris from the matrix also reduced as supported by SEM studies of worn surfaces in subsequent section. As fiber damage decreased, production of wear debris also decreased. During sliding, this debris gets disoriented causing more friction. Higher the wear, higher is the amount of debris and its disorientation and higher is the coefficient of friction. Thus stronger fiber–matrix bonding helps in reducing both, wear and friction in composites. K0 decreased with increase in load which is a general trend for fiber reinforced composites in case of abrasive wear [18–20]. of composites also decreased with load and was in tune to the Lhymn’s equation [21]. 3.6.3. SEM studies of composites Micrographs in Fig. 5(a–h) are arranged in the increasing order of wear performance. Various wear mechanisms which were commonly observed on the surfaces are described in the caption. Micrographs Fig. 5(a), (c), (e) and (g) are for worn surfaces of C0 , CG1 , CG2 and CG3 composites under 10 N while those in Fig. 5(b), (d), (f) and (h) are for 40 N load. When these are compared row wise, influence of increasing load on the topography of a particular composite can be seen. When these are compared column-wise, they show gradual decrease in wear and also in damage of fibers which was responsible for the improved wear performance. Interestingly, increase in fiber–matrix adhesion can also be seen when micrographs are compared column wise. Fiber cracking, cutting, fiber–matrix de-bonding and fiber pullout are the most dominating wear mechanisms along with micro-ploughing of the matrix
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Fig. 5. SEM micrographs (×1000) of surfaces of various composites worn under two extreme loads (a, c, e, and g for 10 N and b, d, f and h for 40 N). Various stages of fiber during shearing action by grit; (1) micro groove formed due to micro cutting of array of fibers; (2) initiation of fiber cracking; (3) fiber cutting; (4) fiber matrix debonding; (5) matrix ploughing; (6) fiber pulverization and (7) fiber pullout.
in these micrographs. Micrograph Fig. 5(a) shows array of fibers (almost naked) in warp and weft direction along with a deep groove ploughed due to abrasion of SiC particle. Fibers in weft direction (perpendicular to sliding direction) show maximum damage and
brittle fracture. Most of the fibers are cut across the diameter. Fibers in warp direction (parallel to sliding direction) showed less damage and different types of fractures. Fiber cracking followed micro-cutting and pulverization are observed phenomena in such
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distortion in the graphitic structure. The enhancement in adhesion between the matrix and CF led to improvement in ILSS of all the composites. Almost 60% increase in ILSS was exhibited by CG3. Overall it was concluded that ␥ treatment to CF proved beneficial for improvement in all the properties including abrasive wear resistance and friction. Highest dose of treatment was most beneficial in these regards. Acknowledgement Authors gratefully acknowledge Dr. P.S. Datta, Principal Scientist, Division of Agriculture Physics, IARI, New Delhi, India for extending ␥-irradiation facility for this work. References Fig. 6. Schematic diagram of fiber tow tension test.
fibers lying in this direction. At various places, these are pulverized and small portions are removed during abrasion as wear debris. The drastic difference in the worn surfaces of composites with untreated and treated fabrics is apparent in the form of amount of resin adhering and protecting the fibers and leading to less and less damage. Micrograph Fig. 5(g) shows so much amount of resin on the surface that very few broken fibers are visible. When fiber–matrix interface is strong, fiber can resist the shearing forces more efficiently and thus resulting in lower wear. Effect of increasing load on the damage of fibers and subsequently resulting in high wear of composites can be seen in Fig. 5, when micrographs Fig. 5(a) and (b); (c) and (d); (e) and (f); and (g) and (h) are compared. Micrographs Fig. 5(b) and (d) show higher depth of grooves due to higher loads revealing multiple layers of fractured fibers. When micrographs Fig. 5(g) and (h) are compared, in spite of high amount of resin protecting fibers, these are still fractured because of higher load. The extents of fiber pull out increase as load increases to 40 N from 10 N. Thus the worn surfaces showed complete correlation with the wear performance and fiber–matrix adhesion. 4. Conclusions Based on the studies on composites developed with PEI matrix and carbon fabric treated with various doses of ␥ rays, it was concluded that the ␥-treatment to CF led to the significant changes in the surface topography of fibers and inclusion of chemical groups such as ether and carbonyl. With increase in dose from 0 to 300 kGy, roughness of the fiber surface increased, as evident from SEM studies and the tensile strength of the fiber decreased. It was also concluded that the ␥ treatment led to the enhancement in the fiber–matrix adhesion as evident from the matrix pick up studies in adhesion test and SEM studies on worn composites. Based on observations in Raman spectroscopic studies (based on ID /IG ratio stresses), it was concluded that stresses induced in the fibers during irradiation (which were direct functions of amount of doses) could be directly correlated with reduction in crystallinity and the
[1] J. Li, F.F. Sun, The effect of nitric acid oxidization treatment on the interface of carbon fiber-reinforced thermoplastic polystyrene composite, Poly. Plast. Tech. Eng. 48 (2009) 701–715. [2] A. Fukunata, S. Ueda, Anodic surface oxidation for pitch-based carbon fibers and the interfacial bond strengths in epoxy matrices, Compos. Sci. Tech. 60 (2000) 249–254. [3] L.Y. Zhang, L.X. Zhao, J.J. Zhang, The effect of fiber oxidation on the tribological behavior of 3D braided carbon fiber/nylon composites, Wear 262 (7–8) (2007) 1026–1030. [4] B.Z. Jang, Control of interfacial adhesion in continuous carbon and Kevlar fiber reinforced polymer composites, Comp. Sci. Technol. 44 (4) (1992) 333–349. [5] M. Sun, B. Hu, Y. Wu, Y. Tang, W. Huang, Y. Da, Surface of carbon fibers continuously treated by cold plasma, Comp. Sci. Technol. 34 (1989) 353–364. [6] Z. Xu, Y. Huang, C. Zhang, L. Chen, Influence of rare earth treatment on interfacial properties of carbon fiber/epoxy composites, Mater. Sci. Eng. A 444 (2007) 170–177. [7] J. Li, Y. Huang, Z. Xu, Z. Wang, High-energy radiation technique treat on the surface of carbon fiber, Mater. Chem. Phys. 94 (2005) 315–321. [8] Y.Z. Wan, Y.L. Wang, Y. Huang, H.L. Luo, G.C. Chen, C.D. Yuan, Effect of surface treatment of carbon fibers with ␥-ray radiation on mechanical performance of their composites, J. Mat. Sci. 40 (2005) 3355–3359. [9] M.M. Hassan, A. El-Hag Ali, G.A. Mahoud, E.A. Hegazy, Synergistic effect of short reinforced fibers and ␥ rays on the thermal and mechanical properties of waste poly(propylene) composites, J. Appl. Polym. Sci. 96 (2005) 1741–1747. [10] J. Li, Y. Huang, S. Fu, L. Yang, H. Qu, G. Wu, Study on the surface performance of carbon fibers irradiated by ␥-ray under different irradiation dose, Appl. Surf. Sci. 256 (2010) 2000–2004. [11] E.N. Hoffman, T.E. Skidmore, Radiation effects on epoxy/carbon–fiber composite, J. Nucl. Mater. 392 (2009) 371–378. [12] J.M. Pintado, J. Miguel, Effect of ␥ irradiation on mechanical behavior of carbon/epoxy composites materials, Cryogenics 38 (1998) 85–89. [13] N. Chand, M. Fahim, Irradiation effects on the abrasive wear of glass fibre–vinylester composites, Tribol. Lett. 3 (1997) 157–160. [14] G.W. Stachowiak, A.W. Batchelor, Engineering Tribology, Elsevier, Amsterdam, 1993. [15] K. Friedrich, Friction and wear of polymer composites, in: K. Friedrich (Ed.), Composite Materials Series 1, Elsevier, Amsterdam, 1986. [16] J. Bijwe, Rekha Rattan, M. Fahim, Abrasive wear performance of carbon fabric reinforced polyetherimide composites: influence of content and orientation of fabric, Tribol. Int. 40 (2007) 844–854. [17] M.J. Matthews, M.A. Pimenta, G. Dresselhaus, M.S. Dresselhaus, Origin of dispersive effects of the Raman d band in carbon materials, Phys. Rev. B 59 (10) (1999) 6585–6588. [18] R. Rattan, J. Bijwe, Influence of weave of carbon fabric on abrasive wear performance of polyetherimide composites, Tribol. Lett. 22 (1) (2006) 105–112. [19] J. Bijwe, R. Rattan, M. Fahim, Abrasive wear performance of carbon fabric reinforced polyetherimide composites: influence of content and orientation of fabric, Tribol. Int. 40 (2007) 844–854. [20] J. Bijwe, J. Indumathi, A.K. Ghosh, On the abrasive wear behavior of fabricreinforced polyetherimide composites, Wear 253 (2002) 768–777. [21] C. Lhymn, K.E. Templemeyer, P.K. Davis, The abrasive wear of short fiber composites, Composites 16 (2) (1985) 127–136.