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Journal of Minerals & Materials Characterization & Engineering, Vol. 5, No.1, pp 87-101, 2006
jmmce.org Printed in the USA. All rights reserved
The Role of Fillers on Friction and Slide Wear Characteristics in
Glass-Epoxy Composite Systems
B. Suresha*1, G. Chandramohan1, J. N. Prakash2, V. Balusamy3 and
1Department of Mechanical Engineering, PSG College of Technology,
Coimbatore- 6 41 004, INDIA
2 Research and Development Centre, East Point College of Engineering. and Technology,
Bangalore-560 025, INDIA
3 Department of Metallurgical Engineering, PSG College of Technology,
Coimbatore- 6 41 004, INDIA
4 Department of Mechanical Engineering, National Institute of Technology,
Trichy-620 015, INDIA
*Corresponding author’s e-mail address: firstname.lastname@example.org
The comparative performance of Glass-Epoxy (G-E) composite systems interfaced with
graded fillers has been examined. In this study, composite materials were experimentally
investigated under varying load and sliding velocities by using a Pin-on-Disc type wear
The influence of two inorganic fillers, silicon carbide particles (SiC) and graphite, on the
wear of the glass fabric reinforced epoxy composites under dry sliding conditions has
been investigated. For increased load and sliding velocity situations, higher wear loss
was recorded. Some of these observations are supplemented by scanning electron
microscopic (SEM) investigations. The coefficients of frictional values show an
increasing trend with subsequent increase in load/sliding velocities. It was observed that
the Graphite filled G-E composite shows lower coefficient of friction than the other two
composites irrespective of variation in the load/sliding velocities. SiC filled G-E
composite exhibited the maximum wear resistance. Further, wear of the matrix, breakage
of reinforcing fibers, matrix debris formation and interface separation were observed in
unfilled and graphite-filled G-E composites. Other interesting SEM features have been
noticed and discussed.
KEYWORDS: Glass-epoxy composite; Fillers; Slide wear; Scanning electron
88 Suresha, Chandramohan, Prakash, Balusamy, and Sankaranarayanasamy Vol.5, No.1
In recent times, there has been a remarkable growth in the large-scale production of
fiber and/or filler reinforced epoxy matrix composites. Because of their high strength-to-
weight and stiffness-to-weight ratios, they are extensively used for a wide variety of
structural applications as in aerospace, automotive and chemical industries . On
account of their good combination of properties, fiber reinforced polymer composites
(FRPCs) are used for producing a number of mechanical components such as gears,
cams, wheels, brakes, clutches, bearings and seals. Most of these are subjected to
tribological loading conditions. The FRPCs exhibit relatively low densities and they can
also be tailored for our design requirements by altering the stacking sequences to provide
high strength and stiffness in the direction of high loading .
A number of material-processing strategies have been used to improve the wear
performance of polymers. Glass fiber reinforced polymeric composites traditionally show
poor wear resistance and high friction due to the brittle nature of the reinforcing fibers.
This has prompted many researchers to cast the polymers with fibers/fillers. Considerable
efforts are being made to extend the range of applications. Such use would provide
economical and functional benefits to both manufacturers and consumers. Various
researchers have studied the tribological behaviour of FRPCs. Studies have been
conducted with various shapes, sizes, types and compositions of fibers in a number of
matrices [3-8]. In general these materials exhibit lower wear and friction when compared
to pure polymers. An understanding of the friction and wear mechanisms of FRPC’s
would aid in the development of a new class of materials so as to counter the challenges
faced by researchers. Reviews of such works found in articles [9-11] have shown that the
friction and wear behaviour of FRPCs exhibits anisotropic characteristics.
Use of inorganic fillers dispersed in polymeric composites is increasing. Fillers not
only reduce the cost of the composites, but also meet performance requirements, which
could not have been achieved by using reinforcement and resin ingredients alone. In
order to obtain perfect friction and wear properties many researchers modified polymers
using different fillers [12-20]. Briscoe et al.  reported that the wear rate of high-
density polyethylene (HDPE) was reduced with the addition of inorganic fillers, such as
CuO and Pb3O4. Tanaka  concluded that the wear rate of polytetrofluroethylene
(PTFE) was reduced when filled with ZrO2 and TiO2. Bahadur et al. [14-16] found that
the compounds of copper such as CuO and CuS were very effective in reducing the wear
rate of PEEK, PTFE, Nylon and HDPE. Kishore et al.  studied the influence of
sliding velocity and load on the friction and wear behaviour of G-E composite, filled with
either rubber or oxide particles, and reported that the wear loss increased with increase in
load/speed. Solid lubricants such as graphite and MoS2 [18, 19] when added to polymers
proved to be effective in reducing the coefficient of friction and wear rate of composites.
Vol.5, No.1 The Role of Fillers on Friction and Slide Wear 89
The use of graphite as a particulate filler has been reported to improve tribological
behavior in metal matrix composites (MMCs) .
Most of the above findings are based on either randomly oriented or unidirectionally
oriented fiber composites. Woven fabric reinforced composites  are gaining
popularity because of their balanced properties in the fabric plane as well as their ease of
handling during fabrication. Mody et al.  have shown that the simultaneous existence
of parallel and anti-parallel oriented carbon fibers in a woven configuration leads to a
synergistic effect on the enhancement of the wear resistance of the composite.
The objective of this work is to investigate the friction and wear properties of
particulate filled G-E composites sliding against a hardened steel counterface. As a
comparison, the friction and wear properties of plain G-E were also evaluated under
identical test conditions. This work helps in understanding the function of different fillers
in G-E composites. This work is believed to be helpful for understanding the function of
different fillers in G-E composites.
Woven glass fabrics made of 360 gsm, containing E-glass fibers of diameter 5-10
µm has been employed. The matrix system used is a medium viscosity epoxy resin
(LAPOX L-12) and a room temperature curing polyamine hardener (K-6) both supplied
by ATUL India Ltd, Gujarat, India. The fillers that have been used are silicon carbide
(SiC) and graphite particulates.
All laminates used in this study were manufactured by dry hand lay up technique.
E-glass plain weave roving fabric, which is compatible to epoxy resin, is used as the
reinforcement. The epoxy resin is mixed with the hardener in the ratio 100:12 by weight.
The stacking procedure consists of placing the fabric one above the other with the resin
mix well spread between the fabrics. A porous teflon film is placed on the completed
stack. To ensure uniform thickness of the sample a spacer of size 3 mm is used. The mold
plates have a release agent smeared on it. The whole assembly is pressed in a hydraulic
press (0.5 MPa) and allowed to cure for a day at room temperature. After demolding, post
curing was done at 120οC for 2 h using an electrical oven. The laminate so prepared has a
size 250 mm X 250 mm X 3 mm. To prepare the filled G-E composites, filler (SiC and
Graphite) is mixed with a known amount of epoxy resin. The details of the composites
are shown in Table 1. The test samples are cut to size 5 mm x 5 mm x 3 mm with the help
of a diamond tipped cutter.
90 Suresha, Chandramohan, Prakash, Balusamy, and Sankaranarayanasamy Vol.5, No.1
Table 1. Details of samples prepared
2.3 Test procedure
A pin-on-disc test setup was used for slide wear experiments. The surface of the
sample (5 mm X 5 mm) glued to a pin of dimensions 6 mm diameter and 22 mm length
comes in contact with a hardened disc of hardness 62 HRC. The counter surface disc was
made of En 32 steel having dimensions of 165 mm diameter, 8 mm thick and surface
roughness (Ra) of 0.84 µm. The test was conducted on a track of 115 mm diameter for a
specified test duration, load and velocity . Prior to testing, the test samples were
rubbed against a 600-grade SiC paper. The surfaces of both the sample and the disc were
cleaned with a soft paper soaked in acetone before the test. The pin assembly was initially
weighed using a digital electronic balance (0.1 mg accuracy). The test was carried out by
applying normal load (30 N to 70 N) and run for a constant sliding distance (5000 m) at
different sliding velocities (3, 4 and 5 m/s). At the end of the test, the pin assembly was
again weighed in the same balance. The difference between the initial and final weights
was a measure of slide wear loss. A minimum of three trials was conducted to ensure
repeatability of test data. The friction force at the sliding interface of the specimen was
measured at an interval of 5 minutes using a frictional load cell. The coefficient of
friction was obtained by dividing the frictional force by the applied normal force.
Selected samples were coated with a thin layer of gold on the worn surface and subjected
to microscopic examination using scanning electron microscope.
3. RESULTS AND DISCUSSION
Experimental data on the slide wear loss of filled and unfilled G-E composite
samples are shown in Figs. 1 to 3 for different loads (30 to 70 N) and sliding velocities (3
to 5 m/s). Table 2 shows the results pertaining to the coefficient of friction of filled and
unfilled G-E composite system. It is observed from the figures and Table 2 that there is a
strong inter-dependence between the friction coefficient and wear loss irrespective of the
loads and sliding velocities employed. The SEM photographs of select combinations of
Matrix Reinforcement Filler wt. %
A Epoxy E-glass fabric Graphite 5
B Epoxy E-glass fabric SiCp 5
C Epoxy E-glass fabric ---- ----
Vol.5, No.1 The Role of Fillers on Friction and Slide Wear 91
filled and unfilled G-E samples subjected to slide wear are shown in Figs. 4, 5 and 6
Sliding ve locit y, m/
Wear loss, g
Figure 1. Wear loss versus sliding velocity of “A” type sample.
Sliding velocit y, m/
Wear l o ss, g
Figure 2. Wear loss versus sliding velocity of “B” type sample.
92 Suresha, Chandramohan, Prakash, Balusamy, and Sankaranarayanasamy Vol.5, No.1
33.5 44.5 5
Sliding velocit y, m/
Wear loss, g
Figure 3. Wear loss versus sliding velocity of “C” type sample.
Table 2. Coefficient of friction of samples tested
Coefficient of friction
A B C A B C A B C
30 N 0.30 0.37 0.38 0.31 0.38 0.41 0.33 0.40 0.43
50 N 0.33 0.40 0.42 0.38 0.45 0.47 0.37 0.51 0.52
70 N 0.35 0.50 0.51 0.45 0.52 0.54 0.42 0.55 0.61
Vol.5, No.1 The Role of Fillers on Friction and Slide Wear 93
94 Suresha, Chandramohan, Prakash, Balusamy, and Sankaranarayanasamy Vol.5, No.1
Figure 4. SEM picture of “A” sample at: (a) 30 N, 3 m/s, (b) 30 N, 5 m/s. (c)
70N, 3 m/s, and (d) 70 N, 5 m/s.
Vol.5, No.1 The Role of Fillers on Friction and Slide Wear 95
Figure 5. SEM picture of “B” sample at: (a) 30 N, 3 m/s, (b) 30 N, 5 m/s. (c) 70N, 3 m/s,
and (d) 70 N, 5 m/s.
96 Suresha, Chandramohan, Prakash, Balusamy, and Sankaranarayanasamy Vol.5, No.1
Figure 6. SEM picture of “C” sample at: (a) 30 N, 3 m/s, (b) 30 N, 5 m/s. (c)
70N, 3 m/s, and (d) 70 N, 5 m/s.
Vol.5, No.1 The Role of Fillers on Friction and Slide Wear 97
3.1 Coefficient of friction
The variation in coefficient of friction with varying sliding velocities/loads of filled
and unfilled G-E composites is shown in Table 2. For the filled G-E composites, an
increasing trend in the coefficient of friction is seen, with increase in sliding
velocity/load. However, comparison of graphite-filled G-E (sample A) with SiC-G-E
(sample B) and G-E composites (sample C) indicate that the coefficient of friction of
graphite filled G-E composite (sample A) is less. The reduction in coefficient of friction
is attributed to the presence of graphite particulates acting as a solid lubricant. On the
other hand, the increase in coefficient of friction in SiC-G-E may occur because of the
inclusion of hard silicon carbide particles.
For the unfilled G-E samples, like in filled G-E samples, an increase in sliding
velocity/load results in increase in the coefficient of friction. The increase in coefficient
of friction is due to the fact that easy detachment of softened epoxy from the
reinforcement and more breakage of reinforced glass fibers.
3.2 Slide wear data
The slide wear data of filled and unfilled G-E composites shown in Figs. 1 to 3 are
considered for interpretation. The results reveal that the wear loss increases with increase
in sliding velocity irrespective of the load employed both for filled and unfilled G-E
composite systems. However, the magnitudes of wear loss values are much less in filled
G-E samples compared to unfilled G-E samples at all loads.
It is seen from Figs. 1 to 3 that the filler in G-E composites appears to influence the
friction and wear behaviour. The wear losses of the composites decreases with filler
addition and show the maximum wear resistance (least wear loss) for SiC-filled G-E and
the least for unfilled G-E).
For C-type sample, the fibers are oriented parallel to the sliding surface and also to
the sliding direction. In this position the fibers can be easily detached from the matrix;
hence it is observed that the increase in wear loss is much greater than that observed in
filled G-E composite samples. Further, increased exposure of the reinforcement of fibers
to the counter surface results in increased fiber fracture due to the frictional thrust.
98 Suresha, Chandramohan, Prakash, Balusamy, and Sankaranarayanasamy Vol.5, No.1
3.3 Scanning electron microscopy
The slide wear data in respect of select samples are discussed based on the scanning
electron microscopic features. The SEM pictures of Sample A shown in Figs. 4(a) and
4(b) pertaining to the test conditions of 30 N, 3 m/s and 30 N, 5 m/s respectively are
considered for interpretation. Thus Fig. 4(a) shows less wear of the matrix, matrix
covering the debris and hardly any breakage of fibers. Fig. 4(b) on the other hand, shows
higher degree of fiber breakage, mostly cleavage type of smaller size and smearing of
debris on the fibers (marked ‘A’ in Fig. 4(b)). The observations corroborate the wear
data reported in Fig. 1. For the same sample at higher load of 70 N, keeping the sliding
velocity at 3 m/s and 5 m/s respectively, Fig. 4c and 4d show the corresponding SEM
features. Thus, Fig. 4(c) displays increased debris formation, agglomeration of debris,
adherence of debris on the fibers and more number of breakage of fibers compared to the
condition seen in Fig. 4(a) (30 N, 3 m/s). Figure 4(d) records increased breakage of fibers
with cleavage type of fracture, interface separation between the fibers and matrix and
debris formation concentrated at specific locations. Further, few fibers along the sliding
direction are found to be disoriented. There is one to one correspondence between the
SEM observations and wear test results.
The SEM picture of B-type sample subjected to a load of 30 N and sliding velocity
3 m/s is shown in Fig. 5(a). The spread of the matrix and fewer wear debris formation are
noticed. Both delamination and debonding increased with increasing sliding velocity (5
m/s), which resulted in exposure of reinforced fibers (Fig. 5(b)) along the sliding
direction. In Fig. 5(c), it is noticed that the debris begins to cluster around the fibers.
When Fig. 5(d) is compared with the Fig. 5(b), it is obvious that with application of
higher load and no change in sliding velocity there has been observed increase of more
breakage of fibers and further the broken fibers show inclined type of fracture. These
observations are in accordance with experimental wear test data presented in Fig. 2.
The SEM features of C- type samples (plain G-E composite) subjected to various
loads and sliding velocities are displayed in Figs. 6(a) to 6(d). Fig. 6(a) shows the SEM
picture of the sample subjected to 30 N load and a sliding velocity of 3 m/s. It is observed
that the matrix wear is more and fiber exposure is less (compare Fig. 6(a) with Fig. 4(a)
and 5(a)). These features support the wear behaviour as seen in Fig. 3. The SEM features
pertaining to 30 N load and 5 m/s sliding velocity is shown in Fig. 6(b), which reveals
that the matrix debris is well spread, yielding more number of glass fiber breakages
compared to the sample subjected to 30 N load and 3 m/s sliding velocity (Fig. 6(a)). By
increasing the load from 30 N to 70 N and keeping the sliding velocity at 3 m/s, the wear
surface features of sample C shows higher wear of the matrix, increased fiber-matrix
debonding as well as breakage of fibers as shown in Fig. 6(c). Increasing the velocity to 5
m/s for the same sample (Fig. 6(d)) results in higher matrix debris formation and heavy
breakage of glass fibers (cleavage type) in large numbers compared to Fig. 6(c) (70 N, 3
Vol.5, No.1 The Role of Fillers on Friction and Slide Wear 99
m/s). Also, the wear debris is getting totally distributed. These SEM photographs
corroborate the wear data shown in Fig. 3.
The following inferences are drawn from the above study.
• Inclusion of Graphite and SiC particulate fillers contributed significantly in reducing
friction and exhibited better wear resistant properties.
• Silicon carbide filled G-E composite shows higher resistance to slide wear compared
to plain G-E composites.
• There has been an observed marked improvement in wear resistance as seen in SiC-
G-E composite sample compared to plain G-E sample.
• Graphite filled G-E composite shows lower coefficient of friction compared to the
other two samples. The reduction in coefficient of friction in A-type sample can be
attributed to the presence of Graphite which acts as a solid lubricant.
• SEM examinations of worn surfaces show that the type of wear changed from
adhesive wear to abrasive wear for all the samples tested.
• Increased wear resistance and reduced coefficient of friction are positive traits, which
make the composite suitable to be used as liners in coal handling equipments.
The authors are grateful to the Additional Director Dr. S. Seetharamu of Central Power
Research Institute, Materials Testing Division, Bangalore for extending the laboratory
facilities for the present study. The authors thank the Central Power Research Institute
management for the permission extended to publish this paper.
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