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Effect of Fiber Loading on Mechanical Properties, Friction and Wear Behaviour of Vinylester Composites under Dry and Water Lubricated Conditions

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International Journal of Material Science IJMS
IJMS Vol.1 Iss.1 2011 PP.1-8 www.ij-ms.org
CWorld Academic Publishing
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Effect of Fiber Loading on Mechanical Properties,
Friction and Wear Behaviour of Vinylester
Composites under Dry and Water Lubricated
Conditions
S.R.Chauhan1, Bharti Gaur2, Kali Dass3*
1 Asst. Prof., Department of Mechanical Engineering, NIT Hamirpur (H.P.) -177005, India
2 Asst. Prof., Department of Chemistry, NIT Hamirpur (H.P.) -177005, India
3 PhD Research Scholar, Department of Mechanical Engineering, NIT Hamirpur (H.P.) -177005,
thakurkalidass999@gmail.com
Abstract-This paper explores the effect of fiber loading on
mechanical properties, friction and sliding wear behaviour of
vinylester composites under dry and water lubricated conditions
under variation of normal applied loads and sliding speeds.
Friction and wear experiments were carried out at ambient
conditions on a Pin on disc machine arrangement. From the
study it has been found that higher fiber content though
improves some of the mechanical properties but also affect
adversely some of the properties. The friction and wear
properties of vinylester are improved by the addition of glass
fiber as reinforced. The coefficient of friction increases with
increase in applied normal load and sliding speed under dry
sliding condition and decreases with increase in the applied
normal load under water lubricated condition, but the specific
wear rate for vinylester composites decreases with increase in
applied normal load under both dry and water lubricated sliding
conditions.
Keywords-Vinylester composites; Mechanical properties;
coefficient of friction; specific wear rate; SEM
I. INTRODUCTION
Polymer composites have been increasingly applied as
structural materials in the aerospace, automotive and chemical
industries, providing lower weight alternatives to traditional
metallic materials. A number of these applications are
tribological components such as gears, cams, bearings and
seals, where the self-lubrication of polymers is of special
advantage. One of the features that make polymer composites
so promising in industrial applications is the possibility of
tailoring their properties with special fillers. Polymers and
their composites are emerging as viable alternative material to
metal based ones in many common and advanced engineering
applications [1-3]. In the industries, the polymers and their
composites are being increasingly used in view of their good
strength and low densities. Besides, a wider choice of
materials and ease of manufacturing make them ideal for
engineering applications [4-6].
On account of their good combination of properties, fiber
reinforced polymer composites are used particularly in
automotive and aircraft industries, the manufacturing of space
ship and sea vehicles [7-9]. Fiber reinforced polymer
composites are the most rapidly growing class of materials
due to their good combinations of high specific strength and
specific modulus. Other important characteristics of these
materials which make them more attractive compared to
conventional metallic systems are low density and ability to
be tailored to have stacking sequences that provide high
strength and stiffness in directions of high loading [10-12].
Polymer composites consist of resin and a reinforcement
two main constituents chosen according to the desired
mechanical properties and the application for which they are
to be employed [13]. Fibers are the principal constituents in a
bre-reinforced composite material. They occupy the largest
volume fraction in a composite laminate and share the major
portion of the load acting on a composite structure [14].
Among the fibre reinforcements glass, fibres are widely
employed. Polymer composites reinforced with these fibres
are usually one to four times stronger and stiffer than their
unfilled matrices. It is also well established fact that no
material is universally resistant to all modes of wear. Hence
during material selection for typical tribo application it
becomes imperative to know its complete spectrum of
behavior in various possible wearing situations [15]. Glass
bre is also used for the bodies of specialty and sports cars.
Glass fibres are electrical insulators, hence their considerable
use in laminates for electrical insulation applications [16].
Glass bers are produced also available in woven form.
Varying density woven glass fabrics determine the
mechanical properties of fabrics [17].
The role of polymer as a matrix in a fibre -reinforced
composite is to transfer stresses between the fibres to provide
a barrier against an adverse environment and to protect the
surface of the fibres from mechanical abrasion. Glass fibre -
reinforced polymer with thermoset polyester resin is an
attractive material that is economically desired. Its application
at low temperatures and under service terms is easy, when this
material is compared to advanced polymer composites with
complex molecule structure, high strength and working under
terms of difficult service [19].
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It is well known that the friction and wear behaviours of
polymers in water lubricated condition differ generally from
those in the dry sliding condition, and the absorption of water
and plasticization of polymer surfaces influence the friction
and wear of the polymer [20]. Also the absorption of water
can lead to reduction in strength, modulus of elasticity,
increase in the elongation and swelling of the surface layer
[21, 22]. Lancaster [23] studied the lubrication of carbon
fibre-reinforced polymers, and concluded that fluids such as
water and other solutions inhibit the formation of transfer
films of carbon/ polymer debris on the counter-face and the
wear rates are greater than those obtained in dry conditions. In
various study of polymer composites with water lubricated
sliding conditions reduces the coefficient of friction but may
increase the wear rate of the polymer composites [23, 24].
Tanaka et al. [24] investigated the wear behaviour of glass
fiber, carbon fiber and carbon bead-reinforced
polytetrafluoroethylene (PTFE). The glass-reinforced PTFE
showed a very low wear rate with a steel counter face and
finally concluded that the fiber preferentially supports the
applied load and a fiber rich layer is produced during rubbing
action on the mating surface. Unal and Mimaroglu [25]
investigated the water lubricated tribological performance of
carbon reinforced PEEK composite and they concluded that
the coefficient of friction under water lubricated condition is
lower than that the dry sliding condition, and he also found
that friction and wear behaviour of PEEK composite also
lead to a reduction of mechanical efficiency. Therefore the
accurate knowledge of the influence of sliding speed and
applied load value on the friction and wear is extremely
important [26].
In recent years, much research has been devoted to
exploring the potential advantage of thermoset matrix for
composite applications [27]. One such matrix is vinylester,
which has found a place in the family comprising the
thermoset engineering polymers due to its excellent
mechanical properties with good chemical corrosion
resistance. It is also known that vinylester resins bond very
well to fiber glass.
Also it is seen from the literature that, a very less amount
of work is carried out on mechanical properties, friction and
sliding wear behaviour of vinylester composites on a steel
disc using a pin-on-disc arrangement under dry and water
lubricated conditions. Thus the aim of the present work is to
study the effect of fiber loading on mechanical properties,
friction and sliding wear behaviour of vinylester composites
under dry and water lubricated conditions.
II. EXPERIMENTAL DETAILS
A. Material and Panel Fabrication
In this investigation mechanical and sliding wear of 2D E-
glass woven fiber in vinylester matrix composite has been
studied. A combination of good mechanical, tribological
properties and relatively lower cost of glass fiber makes them
an attractive alternative for many engineering applications.
The glass fiber chosen is most common type E-Glass fiber
(density 2.54 gm/cm3 and modulus72.4GPa) as reinforcing
material in vinylester composites. The glass fabrics are woven
in two perpendicular directions. The vinylester resin (density
1.23gm/cm3 and modulus 2.4-4 MPa) is supplied by Northern
Polymer Pvt. Ltd. New Delhi. Methyl ethyl ketone peroxide
(MEKP), Cobalt Naphthenate is used as catalyst and
accelerator respectively. The woven glass fabrics composites
consist of fiber in three different quantities 40 wt%, 50wt%
and 60 wt%.
For making of the samples wet hand layup technique is
used. The layup procedure consisted of placing the glass sheet
on the mould release sheet which has been sprayed by the
mould release agent. On this a hardener, accelerator and
vinylester resin mixed in required proportion is smeared. Over
this, a layer of woven fabric sheet is laid down and resin
prepared is spread once again. This procedure is repeated in
all three cases unless the required thickness is obtained. A
metal roller is used so that air bubbles could be removed and
uniform thickness could obtain. After obtaining required
thickness, it is covered once again at top by the mould release
sheet, sprayed by release agent and smeared with layer of
prepared resin. The whole assembly is placed in the
mechanical press and pressure is applied and cured at room
temperature for 24hours. The sheet prepared of sizes 300mm
× 300mm of required thickness. The details of the composites
including weight percentage are shown the Table 1. The test
specimens used for tensile, compression, flexural, ILSS,
Impact, Hardness and wear tests are cut according to ASTM
standards from the respective sheets of fiber percentage
40wt%, 50wt% and 60wt% respectively by sample cutting
saw.
B. Mechanical Properties
The Mechanical Properties such as tensile strength,
compression strength, flexural strength and inter laminar
shear strength (ILSS) were calculated by performing
experiments on Hounsefield-25KN universal testing machines
as per ASTM standard. The toughness tests were performed
on plastic impact tester and hardness was determined on
Rockwell hardness tester.
C. Wear Testing and Test Parameters
To evaluate the friction and sliding wear performance of
vinylester and its composites of glass fiber reinforced
prepared with varying fiber loading under dry sliding
condition, wear tests were carried out in a pin-on-disc type
friction and wear monitoring test rig (DUCOM) as per ASTM
G 99. The counter body is a disc made of hardened ground
steel (EN-32, hardness 72 HRC, surface roughness 0.7 µ Ra).
The specimen is held stationary and the disc is rotated while a
normal force is applied through a lever mechanism. During
the test, friction force was measured by transducer mounted
on the loading arm. The friction force readings are taken as
the average of 100readings every 40seconds for the required
period. For this purpose a microprocessor controlled data
acquisition system is used.
A series of test are conducted with five sliding velocities
of 1.6, 2.2, 2.8, 3.4 and 4m/s under five different normal
loading of 10, 20, 30, 40 and 50N. For finding the specific
wear, weight loss method was used. During these experiments
initial and final weight of the specimens were measured. The
material loss from the composite surface is measured using a
precision electronic balance with accuracy + 0.01 mg. The
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specific wear rate (mm3/N mm) is then expressed on ‘volume
loss’ basis
Where
Ks- is the specific wear rate (mm3N-1mm-1)
M- is the mass loss in the test duration (gm)
ρ- is the density of the composite (gm/cm3)
FN- is the average normal load (N).
III. RESULTS AND DISCUSSION
A. Density and Volume Fraction of Voids
The theoretical and measured densities along with the
corresponding volume fraction of voids are presented in Table
1. It may be noted that the composite density values
calculated theoretically from weight fractions which are not in
agreement with the experimentally determined values. The
difference is a measure of voids and pores present in the
composites. It is clear from the Table 1 that increasing fibre
content from 40wt% to 60 wt%, there is decrease in void
fraction. GV1 composite has the volume fraction of voids
higher compared to other composite specimen GV2 and GV3.
This may be due to the fact that GV1 has 60% matrix material
which may entrap air during the preparation of composite
samples in hand layup technique.
The presence of voids or pores may be due to fibre
interaction and fibre constraints on packing in composite
laminates. This can affect composite performance adversely
which may lead to swelling and reduction in density.
B. Hardness
The variation of composite hardness with the weight
fraction of glass fibre is shown in Fig. 1. For the composite
GV1, the hardness value is recorded as 84HRE while for GV2
as 85HRE and for composite GV3 is measured 87HRE. It is
observed that with increase in the fibre content in the
composite; improves the hardness, though the increment is
marginal. It is well established fact that the strength properties
of polymer composites are mainly obtained from the fibre
contents and fibre strength. So the variation in the strength of
composite with variation of fibre content is obvious.
C. Tensile and Flexural Strengths
These variations of composites GV1, GV2 and GV3 in
tensile and flexural strengths are shown in Figure 2.
Gradual increase in both the tensile and flexural strength
with fibre weight fraction is noticed. Similar observations
have been already made for fibre reinforced thermoplastic
composites. However it may be mentioned that both these
strength properties of the composites are important for
structural application.
Fig.1 Variation of hardness for composites GV1, GV2 and GV3
Fig.2 Variation of strengths for composites GV1, GV2 and GV3
TABLE I
MEASURED AND THEORETICAL DENSITY OF THE COMPOSITES (GV1, GV2 AND GV3)
Materials
Composite Specification
Measured
Density(gm/cc)
Theoretical
density(gm/cc)
Volume
fraction of
voids (%)
Load
(N)
Sliding
speed(m/s)
GV1 (Vinylester+40wt% glass
fibre) 1.95 2.24 10.02
10
20
30
40
50
1.6
2.2
2.8
3.4
4.0
GV2 (Vinylester+50wt% glass
fibre) 2.25 2.36 4.58 10
20
30
40
50
1.6
2.2
2.8
3.4
4.0
GV3 (Vinylester+60wt% glass
fibre) 2.88 2.95 3.67
10
20
30
40
50
1.6
2.2
2.8
3.4
4.0
94
96
98
100
102
104
106
Rockwell Hardness(HRE)
Composites
0
50
100
150
200
250
300
350
400
40
50
60
Strengths(MPa)
Fiber loading(wt%)
T.S.
F.S.
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D. Inter Laminar Shear Strength (ILSS)
When a short beam is subjected to three points bending,
the maximum shear stress (Interlaminar shear stress) occurs in
the beam mid plane (neutral plane) where normal stresses are
zero. This results in combination of failure modes, such as
fibre rupture, micro buckling and interlaminar shear cracking.
The maximum bending stresses (compression and tensile)
occur at the beam upper and lower surfaces. The ratio
(maximum shear stress / maximum bending stresses),
increases as the beam span length to thickness ratio
decreases, and thus the beam is more likely to fail in shear.
An isotropic material in bending will fail in shear if
(maximum shear stress / maximum bending stress), exceeds
0.58 according to the Von Mises criterion. Anisotropic
materials may fail in shear at a lower (maximum shear stress /
maximum bending stress) ratio. Since there is no guarantee
that the specimen in a short beam shear test will fail in
shear, the calculated value is referred to as the apparent
interlaminar strength, which is a lower bound estimate to the
interlaminar shear strength. Interlaminar shear strength
depends primarily on the matrix properties and fibre matrix
interfacial strength rather than fibre properties. ILSS can be
improved by increasing the matrix tensile strength and matrix
volume fraction. The glass fabric composite samples
showed similar responses to those observed in three point
bending. The failed specimen shows that the glass fibre
sample did not reveal interlaminar failure. All these
observations suggest that the glass fabric reinforced
samples failed in bending in the SBS tests.
Fig. 3 Variation of ILSS strength for composites GV1, GV2 and GV3
In the present work the ILSS values are measured for glass
vinylester composites GV1, GV2 and GV3 and an
improvement is recorded in ILSS values with increase in the
fibre content in them. Values are illustrated in the Figure 3.
E. Impact Strength
The study of impact behaviour of fibrous composite
materials is an essential requirement before recommending for
structural and engineering applications. The strength of matrix,
fibre strength, orientation and weight fraction significantly
influence the impact strength of the glass fibre vinylester
composites. In the present investigation since the orientation
is kept same in all three composite samples, the difference in
the impact energy values will be due to the fibre content. The
variation is shown in Figure 4.
Fig. 4 Variation in impact energy for composites GV1, GV2 and GV3
A significant increase in impact strength is observed for
increasing the fibre content from 40wt% to 50wt%. However
with increasing the fibre content beyond this to 60wt%, there
is decrease in the impact strength. Similar results have been
reported in the earlier research. This fact can be considered a
high content of fibres, poor dispersion and distribution of the
fibres in the matrix. It seems that 50wt% of fibers is the
limiting value to increase the impact properties of vinylester
based composites. However at very high wt% of fibers, the
role played by matrix to distribute the stresses developed is
nullified and thus the failure becomes easier.
F. Wear Measurement
In this section friction and sliding wear characteristics of
pure vinylester (V) and E-glass fibre vinylester composites
GV1, GV2 and GV3 under different applied normal loads and
sliding speeds under dry sliding conditions are evaluated.
Table 1 presents the physical properties and test conditions for
the evaluation of coefficient of friction and specific wear rate
of vinylester (V) and glass vinylester composites, GV1, GV2
and GV3.
G. Effect of Normal Load and Sliding Speed on Coefficient
of Friction
The experimental results for coefficient of friction for
glass vinylester composites GV1, GV2 and GV3 tested under
normal loads of 10, 20, 30, 40 and 50N and sliding speeds of
1.6, 2.2, 2.8, 3.4 and 4m/s are shown in Figs. 5(a-c).
Figs 5(a-c) shows the variation in coefficient of friction
with applied normal load under both dry and water lubricated
sliding conditions.
From the Figs. 5(a-c) shows that the coefficient of friction
increases with increase in applied normal load under dry
sliding condition and decreases with increase in the applied
normal load under water lubricated condition. Under all the
test conditions the maximum coefficient of friction was found
to be for vinylester composites GV1 at sliding speed of 4 m/s
and applied normal load of 50N under dry sliding condition,
0
20
40
60
80
100
120
140
160
180
200
GV1
GV2
GV3
ILSS(MPa)
Composites
0
0.2
0.4
0.6
0.8
1
1.2
1.4
40
50
60
Impact Energy(J)
Fiber loading(%)
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and minimum at sliding speed of 1.6 m/s and applied normal
load of 50N under water lubricated dry sliding condition. Also
from the Figs. 5 (a-c) it is observed that coefficient of friction
increases with increase in sliding speed under both dry and
water lubricated sliding conditions. The difference in
coefficient of friction values between water lubricated and dry
sliding conditions has an average of 56.55%. The mean
overall difference is about 57%. But when the applied normal
load increases to the limit load values of the polymer the
friction will increase due to the critical surface energy. Further
it can be explained as the frictional power increases the
temperature of the steel surface, which leads to relaxation of
polymer molecule chains and bond at fibre-matrix gets
weakened. Due to which fibres are broken into fragments and
form debris with matrix particles. Higher the glass fibre
present in matrix more is the frictional resistance in dry
sliding condition. Generally the coefficient of friction for
vinylester and glass vinylester composites under water
lubricated sliding conditions is lower than the dry sliding
conditions. These reductions in coefficient of friction values
are attributed to the part which water plays as lubricant. The
presence of water at the interface of specimen and steel disc
washes away the wear debris. This improves the thermal
properties of specimen considerably and also this results into
assisting of the occurrence of h ydrodynamic contact full film
thickness.
(a)
(b)
(c)
Figs. 5 (a-c) Variation of coefficient of friction with normal load under dry
and water lubricated sliding conditions (a) GV1 (b) GV2 and (c) GV3
(a)
(b)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
5 10 15 20 25 30 35 40 45 50
Coefficient of friction(µ)
Load(N)
1.6m/s(W.L.)
2.8m/s(W.L.)
4.0m/s(W.L.)
1.6m/s(D.S.)
2.8m/s(D.S.)
4.0m/s(D.S.)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
5 10 15 20 25 30 35 40 45 50
Coefficient of friction(µ)
Load(N)
1.6m/s(W.L.)
2.8m/s(W.L.)
4.0m/s(W.L.)
1.6m/s(D.S.)
2.8m/s(D.S.)
4.0m/s(D.S.)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
5 10 15 20 25 30 35 40 45 50
Coeff.of friction(µ)
Load(N)
1.6m/s(W.L.)
2.8m/s(W.L.)
4.0m/s(W.L.)
1.6m/s(D.S.)
2.8m/s(D.S.)
4.0m/s(D.S.)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
5 10 15 20 25 30 35 40 45 50
Sp. wear rate (mm3/Nmm)X10-7
Load(N)
1.6m/s(W.L.)
2.8m/s(W.L.)
4.0m/s(W.L.)
1.6m/s(D.S.)
2.8m/s(D.S.)
4.0m/s(D.S.)
0
0.1
0.2
0.3
0.4
0.5
0.6
5 10 15 20 25 30 35 40 45 50
Sp. wear rate(mm3/N)mmX10-7
Load(N)
1.6m/s(W.L.)
2.8m/s(W.L.)
4.0m/s(W.L.)
1.6m/s(D.S.)
2.8m/s(D.S.)
4.0m/s(D.S.)
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(c)
Figs. 6 (a-c) Variation in specific wear rate with applied normal load under
dry and water lubricated conditions sliding condition (a) GV1 (b) GV2 (c)
GV3
H. Effect of Applied Normal Load and Sliding Speeds
on Specific Wear Rate
The specific wear rate values calculated from mass loss of
E-glass fibre reinforced vinylester composites (GV1, GV2 and
GV3) tested under different testing conditions of load 10, 20,
30, 40 and 50N and speeds of 1.6, 2.2, 2.8, 3.4 and 4.0 m/s are
shown in Figs. 6 (a-c).
The Figs. 6 (a-c) shows the variation of specific wear rate
with applied normal load and sliding speeds under both dry
and water lubricated sliding conditions. From Figs. 6 (a-c) it
is evident from these figures that in this investigation within
load range of 10N-50N, the specific wear rate is influenced by
increasing the applied normal load and the sliding speeds.
From the Figs. 6 (a-c) shows that the specific wear rate for
vinylester composites decreases with increase in applied
normal load under both dry and water lubricated sliding
conditions. The Fig. 6 (a) shows that specific wear rate of
glass vinylester composite GV1 under water lubrication
condition is higher than the dry sliding condition.
It is also noticed that under water lubrication sliding
condition the specific wear rate decreases with increase in
sliding speed. At lower sliding speeds there are differences in
specific wear rates. From the Fig. 6 (b) it is observed that
there is marginal difference in the specific wear rate for both
under water lubricated and dry sliding conditions of
composite GV2. From the Fig. 6 (c) the observations show
that the specific wear rate is lesser in water lubricated sliding
condition than dry sliding condition of composite GV3. It is
also noticed that with increase in sliding speed the specific
wear rate decreases. This is explained by the film layer
formation on counter face in dry sliding conditions whereas in
water lubrication this layer is removed and fresh composite
surface is ready for sliding under water lubricated condition.
(a) (b) (c)
(d) (e) (f)
Figs. 7 SEM pictures of vinylester composites at 50N load and 4.0 m/s sliding speed under dry sliding (a) GV1 (b) GV2 (c) GV3 and water lubricated conditions (d)
GV1 (e) GV2 (f) GV3.
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
5 10 15 20 25 30 35 40 45 50
Sp. wear rate(mm3/Nmm)X10-7
Load(N)
1.6m/s(W.L.)
2.8m/s(W.L.)
4.0m/s(W.L.)
1.6m/s(D.S.)
2.8m/s(D.S.)
4.0m/s(D.S.)
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Water prevents the formation of the transfer films of the
fibre glass/vinylester matrix on the counterface by removing
the debris [8].
The specific wear rate under water lubrication condition is
close to those obtained in dry sliding conditions. More over the
frictional heat loosens the bond between fibre and matrix due
to thermal relaxation, which causes the loss of weight in dry
sliding conditions. However in case of water lubricated
conditions the effect of thermal penetration is avoided by
cooling effect by the presence of water at interface of the
composite specimen and steel disc. The fibre content also
affects the wear behaviour of the glass vinylester composites.
The composite GV3 with 60wt% E-glass fibre reinforcement
shows more compact bond and does not allow the polymer
particles to wear out easily. Hence higher fibre content shows
low wear loss particularly at higher sliding speeds.
I. Scanning Electron Microscopy
Typical SEM features of worn surfaces of E-glass
vinylester composites GV1, GV2 and GV3 at applied normal
load of 50N and sliding speed of 4.0m/s are shown in figure 7.
(a-f) under dry and water lubricated sliding conditions.
The surfaces of the specimens were examined directly by
scanning electron microscope JEOL JSM-6480LV. The
composite samples were mounted on stubs with silver paste. To
enhance the conductivity of the samples, a thin film of
platinum was vacuum-evaporated onto them before the
photomicrographs are taken. The specific wear rate data in
respect of selected samples is hereby discussed based on
scanning electron microscopic features. Figure 7 (a) presents
the features of worn surface of GV1 composite specimen at
applied normal load of 50N and sliding speed of 4.0m/s under
dry sliding conditions.
From the surface the uniform distribution of matrix with
small cracks, debris formation and very small amount of fibre
exposure can be observed. SEM picture shown in figure 7 (d)
presents the features of worn surface under water lubricated
sliding conditions of composite GV1 at applied normal load of
50N and sliding speed of 4.0m/s and it is observed that matrix
is well spreaded and covering the fibres. This shows the
smaller amount of wear in the presence of water as lubricant.
Similarly the figures 7 (b) and 7 (e) present the SEM features
of composite GV2 under dry and water lubricated sliding
conditions at applied normal load of 50N and sliding speed of
4.0m/s respectively. It is observed that under dry sliding
condition fibre breakage, debris formation and fibre exposure
depicting higher wear rate than under water lubricated
conditions representing the fibre exposure with very small
amount of matrix sticking to fibre only and effects of water
acting as coolant and lubricant are seen. Figures 7 (c) and 7 (f)
represent the worn surface features of composite specimens
GV3 under dry and water lubricated sliding conditions at
applied normal load of 50N and sliding speed of 4.0m/s
respectively.The observations of these surface show that wear
of tested composite is lesser under water lubricated conditions.
From this study it is noticed that increasing fibre contents in
vinylester composites there is considerable reduction in
specific wear rate. The effect of load is more pronounced on
composite specimens than the sliding speeds.
IV. CONCLUSIONS
The following conclusions can be drawn from the present
study:
The density of the composite specimens is affected
marginally by increasing the fiber content.
For the composites with higher percentagee of fiber content,
cured at room temperature shows slight increase in density.
Incorporation of higher percentage beyond 50% fiber
loading to 60% has improved the tensile strength, tensile
modulus and elongation. For 50% fiber reinforcement,
composite laminates have maximum values for the flexural
strength, ILSS strength but there is reduction in these
properties when fiber content is increased further to 60%. The
compression strength also reduced with increase in fiber
content from 40% to 50% & 60% for the specimen.
The coefficient of friction increases with increase in
applied normal load and sliding speed under dry sliding
condition and decreases with increase in the applied normal
load under water lubricated condition, but the specific wear
rate for vinylester composites decreases with increase in
applied normal load under both dry and water lubricated
sliding conditions.
The response to friction and dry sliding wear in
vinylester is influenced considerably
by the addition of woven bi-direction glass fiber as
reinforcement and its amount also. The variation in the fiber
content attempted in this work, exhibit lower wear loss
compared to pure vinylester resin. This is due the reason that
pure vinylester has small mechanical properties.
Therefore vinylester with fiber reinforcement improves
load carrying capability that lower the wear rate. Also higher
amount of glass fiber reinforcement reduces the specific wear
rate.
Wear study against Hardened grounded steel disc
counterface under various loads and sliding speeds, the wear
performances of vinylester and glass fiber reinforced
composites with varying fiber loading are ranked as follow.
GV3(Vinylester+60%GFR)>GV2(Vinylester+50%GFR)>G
V1 (Vinylester+40%GFR) > V (Pure Vinylester) (KS in the
order of 10-8mm3N-1m-1) and can be considered as a very good
tribo material. The results are comparable to the epoxies and
other tribo materials.
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