Upload
gkgj
View
216
Download
0
Embed Size (px)
Citation preview
8/19/2019 Dry Sliding Wear Characteristics of Glass Epoxy Silicon Carbide
http://slidepdf.com/reader/full/dry-sliding-wear-characteristics-of-glass-epoxy-silicon-carbide 1/6
Dry sliding wear characteristics of glass–epoxy composite filled
with silicon carbide and graphite particles
S. Basavarajappa n, S. Ellangovan
Department of Studies in Mechanical Engineering, University B.D.T. College of Engineering, Davangere 577004, India
a r t i c l e i n f o
Article history:
Received 19 November 2011
Received in revised form30 July 2012
Accepted 2 August 2012Available online 10 August 2012
Keywords:
Sliding wear
Polymer matrix composites
Wear testing
Surface topography
a b s t r a c t
The dry sliding wear characteristics of a glass–epoxy (G–E) composite, filled with both silicon carbide
(SiCp) and graphite (Gr), were studied using a pin-on-disc test apparatus. The specific wear rate was
determined as a function of sliding velocity, applied load and sliding distance. The laminates werefabricated by the hand lay-up technique. The volume percentage of filler materials in the composite
was varied, silicon carbide was varied from 5 to 10% whereas graphite was kept constant at 5%. The
excellent wear resistance was obtained with glass–epoxy containing fillers. The transfer film formed on
the counter surface was confirmed to be effective in improving the wear characteristics of filled G–E
composites. The influence of applied load is more on specific wear rate compared to the other two wear
parameters. The worn surfaces of composites were examined with scanning electron microscopy (SEM)
to investigate the probable wear mechanisms. It was found that in the early stage of wear, the fillers
contribution is significant. The process of transfer film, debris formation and fiber breakage accounts for
the wear at much later stages.
& 2012 Elsevier B.V. All rights reserved.
1. Introduction
Over the past decades, polymer matrix composites are made
and most widely used for structural applications in the aerospace,
automotive, and chemical industries, and in providing alterna-
tives to traditional metallic materials [1]. The features that make
composites so promising as industrial and engineering materials
are their high specific strength, high specific stiffness and oppor-
tunities to tailor material properties through the control of fiber
and matrix compositions. Composites are developed for superior
mechanical strength and this objective often conflicts with the
simultaneous achievement of superior wear resistance [2]. As a
result of this, these materials are found to be used in mechanical
components such as gears, cams, wheels, impellers, brakes,
clutches, conveyors, transmission belts, bushes and bearings. Inmost of these services the components are subjected to tribolo-
gical loading conditions, where the likelihood of wear failure
becomes greater. Of the large number of matrices available
commercially, only a small portion is in significant use for these
kinds of applications.
The use of fillers in the matrix, gives rise to many combina-
tions that provide increasing load withstanding capability,
reduced coefficient of friction, improved wear resistance and
improved thermal properties. In addition to this, fillers in poly-meric composite reduce the cost due to the less consumption of
matrix material. Fibers are the principal constituents in a fiber
reinforced composite materials. They occupy the largest volume
fraction and share the major portion of the load acting on a
composite [3]. In case of dry sliding it is effective in reducing the
wear rate, this reduction in wear is due to the load carrying
capacity of the fibers, their higher creep resistance and thermal
conductivity. But the higher load makes it more sensitive to fiber
breaking, pulverizing of the fibers and transfer [4]. Generally, the
wear behavior of polymer matrix composites is different from
that of conventional metallic materials. The material removal
from the polymer matrix composites in contact with a counter
surface is characterized by several mechanisms. The primary one
is adhesive wear, wherein fine particles of polymer gets removedfrom the surface, and also fiber–matrix debonding and fiber
breaking. On the other hand, the presence of either the fused
polymer or the grooves at the interface is interpreted to indicate
that the materials are wearing out by abrasion instead of
adhesion [5].
The question of why fibers and fillers usually improve the
wear resistance of a polymer matrix has been the subject of
intense study in recent years [6–9]. Zhang et al. [10] studied
dry sliding friction and wear behavior of PEEK and PEEK/SiC-
composite coatings and concluded that the influences of SiC fillers
in the composite effectively reduce the plough and the adhesion
between the two relative sliding parts. Chauhan et al. [11]
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/wear
Wear
0043-1648/$ - see front matter & 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.wear.2012.08.001
n Corresponding author. Tel./fax: þ 91 8192 2224567.
E-mail address: [email protected] (S. Basavarajappa).
Wear 296 (2012) 491–496
8/19/2019 Dry Sliding Wear Characteristics of Glass Epoxy Silicon Carbide
http://slidepdf.com/reader/full/dry-sliding-wear-characteristics-of-glass-epoxy-silicon-carbide 2/6
reported a study on the effect of SiCp filled glass fiber–vinyl ester
composites on dry sliding wear and water lubricated conditions.
Pure vinyl ester material has higher specific wear rate because of
the lower mechanical properties and reinforcement of glass fiber
and SiC filler improves the wear resistance both under dry and
water lubricated conditions. Basavarajappa et al. [12] studied the
effect of graphite fillers in glass–epoxy composites under dry
sliding conditions. They reported that addition of graphite in
glass–epoxy composite leads to lower wear volume loss. This isdue to a thin coherent and uniform film that was transferred on
the disc and the interphase also contained lubricant particles,
thereby reducing the severity of the wear. Hyung Cho et al. [13]
investigated tribological properties of solid lubricants (graphite,
Sb2S3, MoS2) for automotive brake friction materials wherein it is
reported that the friction stability, fade resistance, anti-fade, and
wear of gray iron disks and friction materials were affected by the
relative amounts of solid lubricants in the friction materials.
Shyam [14] found that wear depends upon the cohesion of the
transfer film, adhesion of the transfer film to the counterface and
the protection of rubbing polymer surface from metal asperities
by transfer film.
Hashmi et al. [15] demonstrated graphite modified cotton fiber
reinforced polyester composites under sliding wear conditions.
They stated that significant reduction in the contact-surface-
temperature was observed on addition of graphite in cotton–
polyester composites. Bahadur and Polineni [16] investigated the
glass fabric-reinforced polyamide composites filled with CuO and
PTFE, and reported that 11.3 vol% glass fabric–25 vol% CuO–
10 vol% PTFE composite showed the lowest steady state wear
rate. It was 60–75% lower than the wear rate that could be
obtained by using glass fabric or CuO reinforcement alone or in
combination. Suresha et al. [17] described the role of SiC and Gr
on friction and slide wear characteristics in glass–epoxy compo-
sites by adding them separately. They stated that the influence of
these inorganic fillers has a significant role in reducing friction
and exhibited better wear resistance properties under dry sliding
conditions.
In view of above an attempt is made in this present investiga-
tion to combine the benefits of two inorganic fillers SiCp and Gr
into the G–E composite, to enhance the wear resistance. The dry
sliding wear behavior of G–E composites was characterized by
observing the scanning electron microscopy (SEM) images. This
approach was adopted to elucidate the mechanism of wear in the
composites.
2. Experimental details
2.1. Specimen details
The matrix material used was a medium viscosity epoxy resin
(LAPOX L-12) and a room temperature curing polyamine hardener(K-6). This matrix was chosen since it provides good adhesive
properties owing to the cross-linking chain between the resin
polymer and the hardener. Hence, the shrinkage after curing is
usually lower. The reinforcement material employed was bidirec-
tional perpendicular yarns of 7-mil E-glass fiber. SiCp (15 mm) and
Gr (15 mm) powders were selected as the filler materials on the
basis of their demonstrated ability to withstand high tempera-
tures, and to form transfer film during sliding and low thermal
expansion. The composites were prepared in the form of blocks
(250 mm 250 mm 3 mm) by the hand lay-up technique. The
fillers SiCp and Gr are mixed with known amount of epoxy resin.
The detail composition of the composite is given in Table 1. The
laminate was cured at room temperature for a period of about
24 h. The cured laminates are cut using a diamond tipped cutter
to yield wear test specimen of size 6 mm 6 mm 3 mm.
Dry sliding wear behavior tests were performed on 6 mm 6 mm
face.
2.2. Test details
A pin-on-disc wear test apparatus was used for the dry sliding
wear experiments (as per ASTM G-99 standard). The disc used
was an alloy steel with 165 mm diameter and 8 mm thick,
hardness of 62 HRc and with a surface roughness of 1.2 mm. The
test was conducted on a track of 130 mm diameter for a specified
test duration, applied load and sliding velocity. The surface of thespecimen was perpendicular to the contact surface. Prior to
testing, the specimen pin was rubbed over a 600-grade SiC paper
to ensure proper contact between the specimen surface and the
disc counter surface during sliding. The surfaces of both the
specimen and the disc were cleaned with a soft paper soaked in
acetone before the test. The initial and final weights of the
specimen were measured by using an electronic digital balance
with an accuracy of 0.0001 g. The difference between the initial
and final weights is the measure of weight loss. The weight loss
was then converted into wear volume using the measured density
data. The specific wear rate (W s) parameter provides a more
comprehensive measure of the wear loss characteristics of the
materials. The specific wear rate was calculated from
W s ¼ DV =Ld ðmm3=NmÞ ð1Þ
where DV is the volume loss in mm3, L is the applied load in
Newton and d is the sliding distance in meters. SEM observations
were carried out; the features of interest regions were recorded.
The specimen being non-conducting, it was sputter coated with a
layer of gold before SEM examination.
3. Results and discussion
When SiCp and graphite fillers are embedded in the G–E
composite, the wear trend is as shown in Figs. 1–3. The specific
wear rate of G–E composite has been found to be affected by the
sliding speed. This is true in both filled and unfilled G–E
composites. In both the cases a general trend has been foundfor the effect of sliding speed as show in Fig. 1.
The effect of sliding speed on wear of polymer matrix compo-
sites has been investigated quite extensively. The specific wear
rate increased as the sliding speed increased. Plowing by the wear
debris and the asperities on the counter surface is the major
activity on the surface. At high speed the interface temperature
increases because of the poor conductivity of the polymer
composite. The high temperature can give rise to a molten layer
at the interface and it can affect the fiber–matrix bonding on the
subsurface. It can also promote degradation wear and crack
propagation on the subsurface. So, the specific wear rate increases
exponentially at higher speeds [18]. The higher thermal conduc-
tivity of the fillers is one of the reasons why filled G–E composites
have superior wear resistance to that of unfilled G–E composite.
Table 1
Details of composites prepared.
Specimen
code
Matrix
volume (%)
Reinforcement
volume (%)
Fillers volume (%)
SiCp Gr
A 50 50 – –
B 40 50 5 5
C 35 50 10 5
S. Basavarajappa, S. Ellangovan / Wear 296 (2012) 491–496 492
8/19/2019 Dry Sliding Wear Characteristics of Glass Epoxy Silicon Carbide
http://slidepdf.com/reader/full/dry-sliding-wear-characteristics-of-glass-epoxy-silicon-carbide 3/6
8/19/2019 Dry Sliding Wear Characteristics of Glass Epoxy Silicon Carbide
http://slidepdf.com/reader/full/dry-sliding-wear-characteristics-of-glass-epoxy-silicon-carbide 4/6
a ploughing action on the surface of the composite. Thus the wear
debris was produced during the sliding process and further
decreased the wear resistance of the composite owing to an abrasive
wear effect.
Contrary to the above, the worn surface of filled G–E compo-
sites has nearly invisible peeling-off at the same sliding condi-
tions. This indicates that the fillers incorporated in the G–E
composite effectively act to enhance the bonding strength amongthe fibers and the matrix. Figs. 5–10 are micrographs of the worn
surfaces of the filled G–E composites in the order of increasing
load, showing that the fillers are protruded from the matrix. The
protrusion of fillers indicates that the fillers take up some portion
of the load during sliding and prevent severe adhesion between
the matrix and the counter surface (Fig. 5). Here the fibers are less
distinctly seen due to smearing by resinous material in which
glass fibers are arranged.
In the absence of severe adhesion the surface fracture is
significantly reduced. The matrix surface is covered with small
shallow and irregular patches of the thin dark film (marked ‘C’ in
Fig. 6) which are different from the markings on the unfilled G–E
composite. Here a few abrasion grooves (marked ‘D’ in Fig. 6) and
a number of ripple markings are exhibited. From Fig. 8, there are
Fig. 4. Worn surface of unfilled G–E composite at 60 N applied load.
Fig. 5. G–E composite filled with 5% SiCp–5% Gr at 20 N applied load.
C
D
Fig. 6. G–E composite filled with 5% SiCp–5% Gr at 60 N applied load.
E
Fig. 7. G–E composite filled with 5% SiCp–5% Gr at 100 N applied load.
Fig. 8. G–E composite filled with 10% SiCp–5% Gr at 20 N applied load.
S. Basavarajappa, S. Ellangovan / Wear 296 (2012) 491–496 494
8/19/2019 Dry Sliding Wear Characteristics of Glass Epoxy Silicon Carbide
http://slidepdf.com/reader/full/dry-sliding-wear-characteristics-of-glass-epoxy-silicon-carbide 5/6
some extent cracks, which are parallel and perpendicular to the
sliding direction (marked arrow). Further, these cracks become
more susceptible to propagation on to the surface, giving rise to
loosening of the fillers. Furthermore, the worn surface gives rise
to laminate type of debris (marked ‘F’ in Fig. 9) when applied loadis increased to 60 N. Hence it can be concluded that an increase in
the volume percentage of filler materials leads to less bonding
between the filler and matrix material. To produce a good
bonding and better wear resistance, an optimum level of filler is
required.
In the case of higher loads most of the matrix material has already
been removed and loosening of the fillers results in exposure of the
fibrous region to the sliding contact. In the regime under adhesive
forces, often transmitted through a film, the fiber ends undergo
severe thinning along their length (marked ‘E’ in Fig. 7); a similar
feature was observed by Hui Zhang et al. [22]. The thinning process
fractures the skin of the fibers and separates it from the surface,
whereas the rest remain embedded, still contributing to the wear
resistance of the composite for a certain time.
By comparing Fig. 10 with Fig. 7, it is possible to highlight the
effect of more SiCp particles in G–E composite. Here the epoxy
matrix and glass fibers are damaged more severely by crushing
and cutting action of abrasive particles (marked ‘G’). The worn
surface shows evidence of poor adhesion of matrix to the fibers as
several clean fibers appear on the worn surface. In fact, this
topography looks more likely as an abrasive wear case rather than
the adhesive wear. As a result the wear rate of the composites
increases slightly with increasing applied load but never reachesvery high levels.
The synergistic effect of fillers hinders the wear of G–E compo-
sites surface layer. Thus, a smoother worn surface and hence lower
wear rate was observed under dry lubrication as compared with
unfilled G–E composite. The better wear resistance exhibited by the
filled G–E composites depends on factors such as increasing
bonding strength, less voids and formation of transfer film by filler
materials.
5. Conclusions
The study of the wear behavior of filled and unfilled G–E
composites at various sliding velocity, applied load and slidingdistance reveals the following.
An increase in sliding velocity increased the specific wear rate.
Applied load has much more predominant effect, whereas sliding
distance has less effect. Inclusion of fillers in G–E composites leads
to better wear resistance; however higher the percentage of the
SiCp filler along with graphite higher the wear due to deteriorated
abrasive wear performance of the parent material and it is also seen
to depend on the amount and nature of the transfer film formed on
the steel counter surface. The wear mechanisms involved are well
indicated with SEM micrographs, which reveal multiple micro-
cracking, debris formation, fiber thinning, fiber breakage, fiber pull
outs, peeling of the matrix and fiber–matrix debonding.
References
[1] Li Chang, Zhong Zhang, Lin Ye, Klaus Friedrich, Tribological properties of epoxy nanocomposites III characteristics of transfer films, Wear 262 (2007)699–706.
[2] W. Giwdon, Stachowiak Andrew, W. Batchelor, Engineering Tribology, thirded., Elsevier, 2005, p. 676.
[3] Hasim pihtili, Nihat Tosun, Effect of load and speed on the wear behavior of woven glass fabrics and aramid fiber-reinforced composites, Wear 252(2002) 979–984.
[4] J. Quintelier, P. De Baets, P. Samyn, D. Van Hemelrijck, SEM features of glass–polyester composite system subjected to dry sliding wear 261 (2006)703–714Wear 261 (2006) 703–714.
[5] P. Sampath kumaran, S. Seetharam, A. Murali, P.K. Kumar, Kishore, Slidingwear studies in glass–epoxy system through scanning microscopic observa-tions, Bulletin of Materials Science 21 (4) (1998) 335–339.
[6] V.K. Srivastava, S. Wahne, Wear and friction behavior of soft particles filledrandom direction short GFRP composites, Materials Science and EngineeringA 458 (2007) 25–33.
[7] B. Suresha, G. Chandramohan, J.N. Prakash, V. Balusamy, K. Sankaranarayanasamy,The role of fillers on friction and slide wear characteristics in glass–epoxycomposite systems, Journal of Minerals and Materials Characterization andEngineering 5 (1) (2006) 87–101.
[8] Xiubing Li, Yimin Gao, Jiandong Xing, Yu Wang, Liang Fang, Wear reductionmechanism of graphite and MoS2 in epoxy composites, Wear 257 (2004)279–283.
[9] Kishore, P. Sampathkumaran, S. Seetharamu, P. Thomasb, M. Janardhana,A study on the effect of the type and content of filler in epoxy–glasscomposite system on the friction and slide wear characteristics, Wear 259(2005) 634–641.
[10] G. Zhang, H. Liao, H. Lia, C. Mateus, J.M. Bordes, C. Coddet, On dry slidingfriction and wear behavior of PEEK and PEEK/SiC-composite coatings, Wear260 (2006) 594–600.
[11] S.R. Chauhan, Anoop Kumar, I. Singh, Sliding friction and wear behavior of vinylester and its composites under dry and water lubricated sliding
conditions, Materials and Design 31 (2010) 2745–2751.
F
Fig. 9. G–E composite filled with 10% SiCp–5% Gr at 60 N applied load.
G
Fig. 10. G–E composite filled with 10% SiCp–5% Gr at 100 N applied load.
S. Basavarajappa, S. Ellangovan / Wear 296 (2012) 491–496 495
8/19/2019 Dry Sliding Wear Characteristics of Glass Epoxy Silicon Carbide
http://slidepdf.com/reader/full/dry-sliding-wear-characteristics-of-glass-epoxy-silicon-carbide 6/6