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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

The fiber reinforced polymer matrix composite (FRPCs) materials

involve two phases namely the reinforcing phase and matrix phase. The

reinforcing phase such as fibers or particles is reinforced in the matrix of

continuous phase. The matrix phase is not only acting as a binder but also it

acts as a load distributing medium to the fibers or particles. In the design of

polymeric matrix composites, selection of matrix materials is based on

application and service conditions of the component. The selection of

reinforcement is based on the properties and the cost that contributes the total

system’s cost (Hull and Clyne 1996).

Adequate literature is available on different aspects of mechanical

and tribological properties of polymer matrix composites by particulate fillers

and fiber loading, length and unidirectional fiber orientation, bidirectional

fiber composites. However very limited literature is available for bidirectional

fiber reinforced polymer matrix composites filled with particulates. The

literature on bidirectional fiber reinforced polymer matrix composites,

reinforcement and matrix use, the effect of filler loading on FRPCs, the

behavior of FRPCs under mechanical loading conditions, wear behavior on

dry sliding and abrasive conditions have been reviewed and discussed in the

following paragraphs.

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2.2 MECHANICAL BEHAVIOR OF FIBER REINFORCED

POLYMER MATRIX COMPOSITES

2.2.1 Effects Due to the Reinforcement of Fibers/Fillers on

Unidirectional Fiber Composites

In order to face the advanced requirements of modern world

applications, many studies have started focusing on investigating and

characterizing materials to obtain newer materials with superior properties.

The required properties of the materials include light weight, high strength,

stiffness and corrosion resistance. Polymer blending has been receiving

increasing attention from both the scientific and industrial communities, as it

being widely accepted as an efficient method. Also, it seems to offer an

alternative low cost substitute for the development of new materials. It also

provides materials with unusual combinations of properties such as

mechanical, thermal, and chemical properties. These are the result of the

different properties of each component. One of the traditional method to

improve the mechanical and tribological properties to make them more

suitable for various loading conditions in polymer tribology is the

incorporation of fibers (e.g., glass or carbon) or filler material (Friedrich et al

2005). Glass, carbon and aramid fibers are some of the widely used

reinforcement materials in polymer matrix composites. The polymer

composites reinforced with these fibers provides four times the strength and

stiffness of unfilled composites (Kurkureka et al 1999).

Advanced polymer composites such as epoxy resins reinforced

with glass or carbon or kevlar fibers or thermoset plastics are finding

applications in almost all general fields of engineering such as automobile,

aero space, marine engineering, materials handling equipments, agricultural

and earth-moving equipment.

31

The mechanical and tribological properties of the FRP composites

were improved by incorporating filler materials and this is a technique

adopted by the various researchers. FRP composites were equipped with the

addition of fillers reinforcement (Lancaster 1972) and lubricants (Xian and

Zhang 2004) in the matrix resin. The fiber and particulate reinforced polymer

composites provide a wide range of properties that could be used in many

applications.

Hussian et al (1996) investigated the mechanical properties of

unidirectional carbon fiber reinforced epoxy composites (C-E) and Al2O3

particles dispersed C-E hybrid composites. They reported that the mechanical

properties were improved by incorporating 10 vol% nano-or micro-sized

Al2O3 particles into the epoxy matrix. The addition of nano or micro sized

Al2O3 particles with the C-E composite was found to provide hybridization

effects. Also increase in the interfacial bonding with fiber and matrix material

was found to be the main reason for improvement.

Hanna et al (2011) investigated the mechanical characterization on

unsaturated polyester resin filled with ceramic particles (CaCO3, CaO,

MgCO3, MgO) and also with fixed amount of 0.5 wt. % of CaF2. They

reported that the values of tensile modulus of elasticity, bending modulus and

hardness increased with all the fillers. Flexural strength of materials filled

with CaCO3, MgCO3 and MgO increases with an increase in weight fraction

of filler particles for MgCO3 and MgO till they reached a maximum value of

9 wt.% for MgCO3 and MgO respectively. Flexural strength of unsaturated

polyester filled with CaO filler particles was found to have a constant value

for all weight fractions when compared to that of other materials.

Harsha and Tewari (2002) studied the mechanical and tribological

properties of various Polyaryletherketones (PAEKs) such as

Polyetheretherketone (PEEK), Polyetherketone (PEK), Polyetherketoneketone

32

(PEKK) with various fillers such as glass fiber, carbon fiber and graphite

particles. They reported that 30% carbon fiber-filled PEKK composites

exhibit improved tensile strength, tensile modulus, flexural strength, flexural

modulus and reduced elongation at break when compared to the 10 and 30%

filled glass and carbon fiber PEEK and PEK composites. Also abrasive wear

studies showed that tougher matrixes of the PAEKs exhibited higher abrasive

wear resistance when compared to their composites. Also the variables such

as sliding distance, load and abrasive grit size seem to have a significant

influence on abrasive wear performance.

Sole and ball (1996) investigated the mechanical and abrasive wear

behavior of the Polypropylene (PP) added with mineral fillers such as talc,

CaCO3, BaSO4 and fly ash.

The addition of the mineral fillers to the PP matrix resulted in a

decrease in the tensile yield strength of the material. The talc filled PP

showed a significant improvement in yield strength over unfilled PP. A slight

improvement in yield strength was identified in CaCO3, BaSO4 filled PP.

Epoxy resin has been significantly important to the engineering

community for many years. Components made of epoxy-based materials have

been providing outstanding mechanical, thermal, and electrical properties.

Using an additional phase (e.g. inorganic fillers) to strengthen the properties

of epoxy resins has become a common practice (Zheng et al 2003). It has

been established in the recent years that polymer-based composites reinforced

with a small percentage of strong fillers can significantly improve the

mechanical, thermal, and barrier properties of the pure polymer matrix.

Ramsteiner and Theysohn (1984) studied the shape and

concentration of reinforcing fillers and the mechanical properties of the

Polypropylene matrix influence the tensile behavior of composites. Filler

33

materials such as glass beads, wollastonite and talcum with different shapes

influence the mechanical properties of the composites. The glass beads with

regular shape were found to provide better mechanical properties for

polypropylene composites.

Bahadur et al (1990) investigated the mechanical and tribological

behavior of the reinforcement of short glass fiber with thermosetting polyester

composites. They reported that an increased proportion of fiber-glass in

polyester increases the flexural modulus of the composites. They also

reported that the wear rate of polyester composites is much lower than that of

the unreinforced polyester.

2.2.2 Effects due to Fiber Length and Orientations

The performance of the FRP composites is mainly due to the fiber

length and orientations. Length of the fibers can be long or short. Long,

continuous fibers are easy to orient and process, but short fibers cannot be

controlled fully for proper orientation. Long fibers provide many benefits

over short fibers such as impact resistance, low shrinkage, improved surface

finish, and dimensional stability. However, short fibers are more effective

cost, easy to work with, and have a fast cycle time fabrication procedures.

Short fibers have fewer flaws and therefore, higher strength as well.

Fibers oriented in one direction give very high stiffness and

strength in that direction. If the fibers are oriented in more than one direction,

such as in a mat, they provide high stiffness and strength in the directions of

the fiber orientations. However, for the same volume of fibers per unit

volume of the composite, it cannot match the stiffness and strength of

unidirectional composites.

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Fu et al (2000) investigated the tensile properties of PP reinforced

with Short Glass Fibers (SGF) and Short Carbon Fibers (SCF) composites.

They reported that mean glass and carbon fiber lengths decrease with

increasing fiber volume fractions. Also, the combined effect of fiber volume

fraction and fiber length determines the final tensile properties of the

composites. The composite strength and modulus of the SCF is higher than

SGF composites. Moreover, it was noticed that the tensile failure strain of the

composites decreases with an increase of fiber volume fraction.

Friedrich (1985) studied the fracture toughness of glass fiber

composites with various matrix materials such as ETFE (ethylene

tetrafluroethylene), PET (poly ethylene terepthalate) and PPS (polyphenylene

sulfide). He reported that the improvement of fracture toughness by the

addition of short fibers is highest when the matrix is in a brittle condition.

Also fiber aspect ratio, interfacial bond strength and fiber strength and

stiffness are some of the factors considered for the composite toughness

improvement.

Gates et al (2003) performed the tensile and compressive strength

and stiffness evaluation on five different laminate configurations

(Unidirectional and angle ply laminates [0], [90], [±25], [±45], [45/90/-45/0])

of carbon fiber reinforced polyamide matrix composites under the cryogenic

temperature conditions. In the case of tension loading, longitudinal and

transverse stiffness and strength decreased as test temperature decreased. But

the tensile shear modulus and strength increased with a decrease in

temperature. Also, for tension loading, the [45/90/-45/0] and [±25] laminates

were less influenced by temperature than the other laminates considered.

However, the [45/90/-45/0] laminate was more sensitive to cryogenic

temperatures than the [±25] laminate. For compression loading, cryogenic

temperatures produced an increase in both the modulus and strength of the

35

laminates. The greatest increase in compressive strength occurred in the [90]

and the greatest increase in modulus occurred in the [±45] laminates.

Keusch et al (1998) investigated the influence of the interface of

differently sized glass fibers on the mechanical properties of glass fiber

reinforced epoxy resin composites. All other parameters are kept constant. To

characterize the fiber/matrix adhesion mechanical tests were conducted and

the results revealed. An investigation of the tensile fatigue performance of

cross ply laminates with two different sizing in the 0° and 90° layers revealed

that the best fatigue performance is determined for composites with a good

fiber/matrix interaction in both layers.

The influence of surface treatments such as oxidation and sizing on

a high strength unidirectional carbon fiber reinforced cynate matrix composite

for interfacial fiber matrix adhesion and Interlaminar Shear Strength (ILSS)

properties were studied by Marieta et al (2002) using the single pull out test.

The carbon cynate composite shows that a higher ILSS due to powerful

interfacial bonds led to a high adhesion effect.

Zhang et al (2004) performed two different surface treatments such

as air oxidation and cryogenic treatment on pitch based short carbon fibers of

epoxy matrix composites. They investigated the mechanical properties such

as flexural modulus and strength. Surface roughness of the carbon fiber

significantly increased by both oxidative and cryogenic treatments,

accordingly to improve the interfacial adhesion strength of fiber and epoxy

bonding due to the mechanical interlocking. Hence, improved mechanical

properties on surface treated short carbon fibers were reported. Also, the

cryogenic treatment has some advantages such as short treatment time and

36

environment-friendly media and higher improvement on both modulus and

strength when compared to the oxidative one.

2.2.3 Effects due to Bidirectional Fibers

Suresha and Sivakumar (2009) studied the mechanical and two

body abrasive wear behavior on bidirectional Glass Vinyl ester (G–V) and

Carbon Vinyl ester (C–V) composites. They reported that the C-V composite

exhibits a higher tensile strength when compared the G-V composite. This is

because in the carbon fibers, the carbon atoms are bonded together in

microscopic crystals that are aligned parallel to the axis of the fiber. The

crystal alignment makes the fiber incredibly strong for its size. Various

properties of carbon fiber such as high tensile strength, low weight, and low

thermal expansion contribute to enhanced tensile strength. Further, the high

strength carbon fabric reinforcement in vinyl ester lowers the elongation at

fracture. The C-V composite was found to exhibit a better wear resistance

when compared to the G-V composites.

Kim et al (2004) studied the mechanical properties of the carbon

woven fabric composites and stated composites could be damaged during the

fabrication process, transport, storage and maintenance. They are susceptible

to mechanical damages when they are subject to effects of tension,

compression and flexure, which can in turn lead to interlayer delamination. In

any case, an increase in external load favors the propagation of delamination

through the interlayer, leading to the catastrophic failure of the component.

Vishwanath et al (1992) examined the mechanical and sliding wear

behavior of glass/polyester and glass/phenolic composites with three different

weight percentages of matrix for the effect of matrix content of composites.

They revealed that the 20 wt.% of the matrix resin in both the composites

yield better tensile and flexural strengths. Also 30 wt.% of matrix resin in

37

both composites showed a minimum wear rate and minimum friction

coefficient. A comparison between the two composites the glass/phenolic

composite showed a minimum wear rate and friction coefficient.

Wonderly et al (2005) investigated the biaxial glass fiber/vinyl

ester and carbon fiber vinyl ester for mechanical properties such as tensile

strength and impact strength. They reported from the results that the carbon

fiber/vinyl ester composite proved mechanically superior under loading

conditions, where the strength is mainly fiber dominated, i.e. under tensile

loading and indentation. Since the carbon fiber composite has higher specific

strengths, lower density, as well as considerably higher stiffness, a carbon

fiber ship could be built significantly lighter than a glass fiber. Both

composites exhibited excellent properties and demonstrated suitably of use in

large ships.

Ramakrishna and Hull (1994) studied the tensile properties on the

bidirectional carbon fabric reinforced epoxy (C-E) composites. They reported

that the resin matrix cracking, fiber bundle debonding and tensile fracture of

fiber bundles are the reasons for collapse the laminates under tensile loading.

They also observed that the tensile properties of the C-E composite increased

with an increase in fiber content.

Gilchrist et al (1996) investigated the mechanical behavior of both

unnotched and web and flange-notched continuously reinforced unidirectional

and bidirectional carbon-fiber/epoxy and glass-fiber/epoxy I-beams under

static load. Buckling and failure of the glass/epoxy beams occur at loads that

are approximately 75% of the corresponding loads in the carbon/epoxy

beams. A higher tensile strength and modulus of the carbon/epoxy composite

when compared to the glass/epoxy composites were also reported.

38

Suresha et al (2008) investigated the mechanical and three-body

abrasive wear behavior of two (2-D) and three dimensional (3-D) E-glass

woven fabric reinforced vinylester (G-V) composites. They reported

improved tensile properties such as tensile strength, tensile modulus and

elongation at break in the 3-D G-V composites when compared to the 2-D

composites. They further reported that the wear volume loss of both 2-D and

3-D G-V composites increased with an increase in abrading distance/load,

even though the highest wear rate was obtained for 2-D G-V composites

when compared to 3-D G-V composites.

Jane Maria et al (2006) investigated the carbon-epoxy (C-E)

composites with four different laminate families (F155/PW, F155/HS,

F584/PW and F584/HS) using pre-impregnated materials based on F155TM

and F584TM epoxy resins reinforced with carbon fiber fabric styles Plain

Weave (PW) and Eight Harness Satin (8HS). They reported that the tensile

test results showed that the laminates with modified F584-epoxy matrix

present higher mechanical properties when compared to the F155-epoxy

matrix. The F584/PW family presented the highest tensile strength value and

the F584/8HS the highest modulus. This is because the used modifier

presented a good compatibility with both F584 epoxy matrix and carbon fiber

reinforcement.

Shivakumar et al (2006) studied the mechanical characterization of

two different polymer composites made of E-glass fibers and carbon fibers

reinforced with vinyl ester resin. They reported that the carbon

fiber/vinylester composite showed an improved tension, compression,

in-plane shear, and interlaminar shear properties when compared to glass

fiber composites.

39

2.2.4 Effects due to Bidirectional Fibers with Fillers

Suresha et al (2010) investigated the mechanical and three-body

abrasive wear behavior of carbon-epoxy (C-E) composites both with and

without the use of graphite fillers. They reported that the incorporation of

graphite fillers with the C-E composites enhanced the hardness and tensile

strength of the composites. They further reported that the specific wear rate

showed the decreased trends for graphite filled C-E composite when

compared to unfilled C-E composite.

Carbon–phenolic woven fabric composite materials are used in

heavy duty bearings due to their natural self-lubricating properties and

thermal stability. Park et al (2006) developed the hybrid Composite

Hemispherical Bearing (CHB) for high mobility tracked vehicles using

carbon-phenolic woven composites to improve the sufficient through-

thickness compressive strength and wear resistance. The results revealed that

the addition of 8% carbon black and 10% PEEK powders by weight reduces

the friction coefficient of the PAN based carbon–phenolic composite. Also, it

was found that the endurance life of newly developed CHB increased by three

times more than that of the conventional carbon-PEEK CHB. The wear depth

was found to be five times smaller when compared to conventional carbon-

PEEK CHB.

VaradaRajulu et al (2002) investigated the tensile properties of

epoxy toughened with hydroxyl terminated polyester composites with

different layers of glass woven rovings reinforced into this matrix. They

reported that the tensile strength increased with the increase in weight fraction

of rovings. This is due to the good bonding between the matrix and the

reinforcement because of the use of coupling agent.

40

Biswas and Satapathy (2010) conducted the tribological and

mechanical investigation on alumina filled glass-epoxy composites. The

results revealed that alumina filled glass-epoxy composite exhibited lower

mechanical properties even though it showed a superior wear performance

when compared to other materials.

Sujesh and Ganesan (2012) investigated the tensile behavior of

bidirectional woven Glass Fiber Reinforced Epoxy Polymer (GFRP)

composites filled with nano silica. He reported that reinforcement of nano

silica with the composite increases the stiffness with damage free range. Thus

the silica compensates for the weak mechanical properties of GFRP

composite, even though the tensile result showed a slight decrement in

ultimate tensile strength and tensile modulus of the composites.

Faltermeier et al (2007) investigated the mechanical properties of

uni-directional and bi-directional glass fiber reinforced urethane

dimethacrylate filled with the SiO2 composite brackets and unfilled composite

brackets. They reported that the reinforcement of SiO2 fillers with composites

improve the fracture strength and fracture toughness when compared to

unfilled composite brackets. Further, they also reported that the glass fiber

reinforcement of composite brackets resulted in an enhancement of the

mechanical properties.

Shivamurthy et al (2009) investigated the influence of particulate

filler such as SiO2 (3, 6 and 9 wt. %) with the E-glass woven fabric-epoxy

(G-E) composites on mechanical and wear behavior. Increased mechanical

properties such as Young’s modulus, flexural strength and surface hardness

through the enhanced interlaminar shear strength were reported. This is

because of the addition of SiO2 fillers with G-E composites.

41

Ismail et al (2012) investigated the mechanical and erosive wear

behavior of carbon fabric reinforced epoxy (C-E) composites filled with

different weight proportions of fly ash cenosphere (CSP). They reported

improvement in mechanical properties such as tensile modulus and flexural

modulus of CSP filled C-E composites when compared to unfilled C-E

composites. This is because of low density and higher silica content of CSP

filler.

The literature seems to clearly indicate that the type of fiber, fiber

orientation, matrix material and type and shape filler materials influences the

mechanical ability such as strength and stiffness of the polymer composite

materials. The addition of filler materials with polymer matrix composites

seems to enhance the mechanical as well as tribological properties. The newly

developed hybrid bidirectional composites with the addition of silane-treated

silicon carbide fillers with different volume fractions tailored might contain

potential for improving the mechanical properties. However, this has not been

adequately supported by relevant studies. So the knowledge of function of

bidirectional fiber reinforced polymer matrix composite filled with silane-

treated silicon carbide particles is required to support the light weight

aerospace and bearing applications. The current study is an attempt towards

this discussion.

2.3 DYNAMIC MECHANICAL ANALYSIS

Dynamic Mechanical Analysis (DMA) is a method where a small

deformation is applied to a sample in a cyclic manner. This allows the

materials response to stress, temperature, frequency and other values to be

studied. DMA applies an oscillatory force at a set frequency to the sample and

reports changes in stiffness and damping. DMA data is used to obtain

modulus. It is a useful method of detecting relaxations in polymer molecules

as the temperature is scanned over a range from sub ambient to above the

42

material’s glass transition investigating the structures and viscoelastic

behavior of polymeric materials to determine their relevant stiffness and

damping characteristics for various applications.

Fibers are thought to be the most effective reinforcement phases for

polymer materials; the fiber-reinforced composite materials always exhibit a

high mechanical performance. Carbon fibers, in particular exhibit superior

properties such as higher Young’s modulus, better strength, better thermal

conductivity and good electrical properties when compared to other fibers.

Therefore, carbon fibers are currently being extensively used reinforcements

for composites because of their availability and reliability.

Lofthouse and Burroughs (1978) studied the thermo mechanical

properties of the thermosetting, thermopolymers and metal glasses by DMA.

Ghezzo et al (2010) conducted the DMA of carbon fiber reinforced with

bismaleimide tetrafuran matrix composite to study the self-healing properties

of composites.

DMA of epoxy/expanded graphite (EG) and polyester/EG

composites, epoxy/expanded-milled graphite (epoxy/milled-EG) and

polyester/expanded-milled graphite (polyester/milled-EG) composites were

carried out by Jia et al (2005). The results showed that glass transition

temperature of the epoxy increased by the addition of EG and milled-EG

fillers. Milled-EG increased the storage modulus of the epoxy.

Goyal et al (2007) studied the dynamic mechanical properties of

high-performance polymer matrix composites based on semi-crystalline

polyetheretherketone (PEEK) matrix with aluminium oxide (Al2O3) loading.

A composite containing the 68 wt% of Al2O3 increased the storage modulus

by 78% at 50°C and 200% increase at 200°C, even though there was no major

change in mechanical loss factor with the addition of Al2O3.

43

Kanagaraj et al (2008) reported that to increase the mechanical

properties of the High-Density Polyethylene (HDPE), 1 wt. % of Carbon

Nanotube (CNT) was added. The material was tested by Dynamic Mechanical

and Thermal Analyzer (DMTA) and the results revealed that the storage

modulus of the CNT-mixed HDPE increased, thus confirming the reinforcing

effect of CNT with HDPE leading to improved mechanical properties.

Yasmin and Daniel (2004) studied the mechanical and thermal

properties of graphite platelet/epoxy composites and reported that the storage

modulus and glass transition temperatures of the composites increased with

an increase of graphite platelet concentration; however, the coefficient of

thermal expansion decreased with the addition of graphite platelets. Yasmin

et al also found that a higher concentration of the graphite increases the

thermal stability of the composite than the pure epoxy.

Afaghi-Khatibi and Mai (2002) investigated the interfacial

properties of the carbon epoxy(C–E) composites but with two types of fiber

surface treatments, oxidized/sized and untreated, respectively using the DMA.

They reported that C–E samples with oxidized/sized fiber expose less

fiber/matrix interfacial degradation when compared to the untreated C–E

composite.

Wagge et al (1991) reported the effects of the addition of various

fillers and extenders (clay, pecan shell flour, and wheat flour) on the curing

process of a phenol-formaldehyde resin by Dynamic Mechanical Thermal

Analysis (DMTA). The DMTA results showed that the curing process of

composite was not affected by any fillers or extenders and also minor

differences in the physical properties of the uncured resin.

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Yuanxin et al (2012) investigated the effect of clay weight fraction

on thermal and mechanical properties of epoxy matrix of the unfilled, 1, 2, 3,

and 4 wt% clay filled SC-15 epoxy using DMA. They reported that the 2.0

wt% clay filled epoxy exhibit a higher storage modulus and glass transition

temperature (Tg). They also investigated the carbon fabric reinforced

nanophased epoxy with 2 wt% clay by DMA, and revealed that an increase of

5°C of Tg when compared to the plain composite.

Costa et al (2005) studied the cure behavior of the carbon-epoxy

thermosetting composite by DMA used to produce the composite material

with certain quality that can be used in structural components.

Goertzen and Kessler (2007) studied the viscoelastic behavior of

carbon fiber epoxy matrix composites used for pipeline repair by DMA. They

reported the glass transition temperatures for various stages from room

temperature to post cured composite specimens and also identified the

temperature limits for the composite.

Normally, the components made of polymer-based composites are

subjected to thermal stresses and abrasion while it is in the usage under

various loads. One of the techniques followed by researchers to combat this

problem is to improve the tribo-mechanical properties of polymer-based

composites, which includes addition of the filler materials to the polymer-

based composites; the DMA was followed to study the influence of thermal

properties on composite materials at elevated temperatures. The dynamic

mechanical analysis on silane-treated SiC particulate filled carbon-epoxy

composites system has not been reported in literature. Hence the viscoelastic

properties such as storage modulus, loss modulus, damping and glass

transition temperature (Tg) of the materials will be discussed in this study.

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2.4 FRICTION AND DRY SLIDING WEAR BEHAVIOR OF

FIBER REINFORCED POLYMER MATRIX COMPOSITES

2.4.1 Wear and Friction Coefficient

Wear is defined as damage to a solid surface, generally involving

progressive loss of material due to relative motion between that surface and

contacting substance or substances. Friction is defined as the resistance to

movement of one solid body over another. The importance of tribological

properties convinced many researchers to study the friction and wear behavior

and to improve the wear resistance of polymeric composites.

The need for the use of newer materials to combat wear situations

has resulted in the emergence of polymer-based composite materials.

Fiber-reinforced polymeric composites are one of the most rapidly growing

class of materials because of their good combination of high specific strength

and specific modulus. They are widely used for sliding couples against

metals, polymers and other materials. However, where there is contact, there

is the problem of friction and wear. In the case of fiber reinforced polymer

matrix composites, the process of material removal in dry sliding condition is

dominated by four wear mechanisms, viz, matrix wear, fiber sliding wear,

fiber fracture and interfacial debonding (Friedrich 1985). In tribological

applications, these composites are subjected to conditions such as rubbing,

sliding and rolling against themselves or against other materials. The

tribological performance of composite materials is usually related to their

reinforcement properties. One of the traditional methods to improve the

friction and wear behavior of polymeric materials was to enhance their

hardness, stiffness and compressive strength and to reduce their adhesion to

the counterpart material (Lhymn 1987).

46

Myshkin et al (2005) reviewed the tribological behavior of

polymers and studied the surface energy of different coatings by new contact

adhesion meter. They reported results related to friction of plastics, effect of

load, sliding velocity and temperature on friction, abrasive and adhesive wear

and friction on polymers.

2.4.2 Effect of Reinforcement of Fillers/Fibers in Unidirectional

Composites

A notable advance in the polymer industries has been the use of

fiber and particulate fillers as reinforcement in polymer matrix. However, the

matrix materials also play an important role as is the case for thermoset resin

matrix composites, which can be designed for specific applications by

properly selecting the polymer.

Some of the commonly used polymers include

polytetraflouroethylene (PTFE), polyetheretherketone (PEEK), polyamide,

polyethylene, phenolic, vinyl ester, unsaturated polyester and epoxy. Fillers

affect the tribological behavior of polymers by decreasing wear in some cases

and while increasing the same in others. Many researchers have reported an

improvement in wear resistance of polymers by the addition of fillers. Some

of the fillers that are effective in reducing friction and wear are MoS2, CuO,

CuS, Al2O3, etc.,.

When compared to fillers with reinforcements and matrix resins,

fillers are least expensive and also save weight in the case of polymer

composites. The use of fillers with the polymer composites is considered to

be important due to following reasons:

i. Fillers improve the wear resistance of the composites

47

ii. Fillers enhance the mechanical properties of the composites

by transferring stresses and by improving the bonding

between the reinforcement and matrix.

iii. Fillers reduce the shrinkage of the polymer composites

iv. Fillers reduce the cost of the composite by reducing the

quantity of costlier resin and reinforcement fibers

v. Fillers influence the fire resistance of composites.

Li et al (2004) reported that the switch slide base plates are made of

epoxy with graphite and MoS2 fillers. In the dry sliding test, both the graphite

and MoS2 act as friction-reducing agents. The wear resistance of the epoxy

with graphite was found to be 10 times higher than that of the neat epoxy.

They concluded that during the wear process, the formation of a thin transfer

film on the counterface was responsible for the reduction in friction and wear

loss of filled epoxy composites. The MoS2 prevents the adhesion between the

steel ring and resin counterpart. This wear resistance of the material was due

to the stability of the transfer film on the counterface of the disc under dry

sliding test.

Suresha et al (2007) investigated the role of SiC fillers in glass-

epoxy (G-E) composites on mechanical and dry sliding wear behavior. They

reported that the mechanical properties such as tensile strength, tensile

modulus, and elongation at break, flexural strength, and hardness improved

due to the inclusion of SiC filler. Also, the dry slide wear test results of

SiC-G-E composite showed a lower slide wear loss irrespective of the

load/sliding velocity when compared to G-E composite.

Fillers and fiber reinforcement increase the strength and stiffness of

a polymer, and hence, are effective in reducing wear in dry sliding conditions

48

involving adhesion transfer or fatigue. Bijwe et al (1990) studied the effect of

filler/fiber reinforcement in four types of polymers which may increase or

decrease the wear rate. They reported that the specific wear rate decrease with

an increase in load. Except for bronze-filled polytetrafluoroethylene (PTFE),

all other fillers such as carbon, graphite, PTFE and MoS2 short glass fibers

increase abrasive wear. This is because the extent of counterface modification

in multipass conditions is an important parameter in measuring the abrasive

wear performance of the composites.

Jia et al (2005) studied the wear and transfer characteristics of four

carbon fiber reinforced polymer composites such as Polytetrafluoroethylene

(PTFE) reinforced by 15% Carbon Fiber (CF), Polyimide (PI) reinforced by

15% CF and 5% PTFE, PI reinforced by 15% CF and 5% MoS2 and

Polyetheretherketone (PEEK) reinforced by 15% CF and 5% PTFE under

distilled-water-lubricated and dry-sliding against stainless steel. They

reported that all four composites under the water-lubricated conditions

exhibited lower friction and better wear resistance when compared to dry

sliding conditions because of composite transfer on to the counterpart steel

surface accounted for the larger wear rate of the polymer composite under dry

sliding, its hindered transfer onto the steel surface and the boundary

lubricating action of water accounted for the much smaller wear rate under

water lubrication.

Prehn et al (2005) studied the sliding wear performance of

SiC-filled epoxy composites under abrasive and water-lubricated conditions

for pump applications. To combine the ductility of the polymer with the

hardness of the ceramics, SiC was used as a filler material. They concluded

that incorporation of SiC in epoxy showed excellent wear behavior under dry

and water-lubricated conditions.

49

Srivastava et al (1992) investigated the friction and wear properties

of unidirectional E-glass fiber reinforced epoxy resin filled with mica

particles. They reported that the addition of mica fillers reduces the wear rate

and friction of the E-glass-epoxy composite. They also noticed that an

increase in the hardness and compressive strength of unidirectional E-glass

fiber reinforced epoxy resin composites.

Srivastava and Pathak (1996) studied the effect of graphite

particulates on friction and dry sliding wear of short glass fiber reinforced

epoxy matrix composites. Bushing samples were prepared by short glass

epoxy composites with various percentages of graphite filler materials.

Bushing samples was tested for wear and friction study. The results revealed

that both the wear and friction increased with the increase in loads and sliding

velocity. However, with an increase in the the value of graphite (10%), the

value of wear decreases irrespective of the applied load and the sliding

velocity. This is due to the formation of the lubricating transfer film by

graphite at the countersurface which reduces wear rate.

Davim and Cordoso (2009) conducted dry sliding wear test on

polyetheretherketone (PEEK), 30 wt% carbon fiber filled PEEK

(PEEK-CF30), 30wt% glass fiber filled PEEK (PEEK-GF30) against steel

and reported that the PEEK-CF30 shows a lesser friction coefficient when

compared to PEEK-GF30 and PEEK. PEEK-CF30 and PEEK-GF30 materials

both shows improved wear resistance when compared to PEEK even though

PEEK-CF30 exhibits best tribological character.

Bloom et al (2003) studied the wear resistance of Al-Cu-Fe

quasicrystal filled with novolac epoxy composite materials under dry sliding

conditions. They reported that when epoxy filled with aluminum, copper,

iron, aluminum oxide, and silicon carbide are tested for comparison, the use

50

of Al–Cu–Fe quasicrystal powder as filler in epoxy, maximizes the composite

wear resistance while also minimizing abrasion of the steel counterface.

The tribological behavior of Polyphenylene Sulfide (PPS) filled

with the inorganic fillers Ag2S, CuS, ZnF2, and SnS were investigated under

dry sliding conditions by Schwartz and Bahadur (2001). They reported that

when Ag2S and CuS fillers are deformed plastically, they produce smooth

countersurface leading to lower wear rate. However, ZnF2 and SnS did not

show any deformation. It produces rough surface and deep cracking at the

higher wear rate. The flexural strength of the Ag2S and CuS composites were

found to be much higher than that of the ZnF2 and SnS.

Yamaguchi (1990) found that the wear rates of unsaturated

polyester and epoxy matrices filled with different proportions of silicon

dioxide decreased significantly at a higher loading of 40 wt. %.

Brisco et al (1974) studied the friction and wear behavior of

polythenes with and without lead oxide, copper oxide fillers with the

influence of sliding speed, load and the nature, roughness and temperature of

the counterface. They reported that both lead oxide and copper oxide mixed

filler drastically reduces wear but not the friction of high density polythene.

Also in low density polythenes, no such wear reduction was found. In high

density polythenes, wear at high speeds were reduced due to smooth steel

counterfaces

Suresha et al (2010) investigated the role of micro and nano fillers

such as graphite and nano clay respectively on Polyamide66/polypropylene

(PA66/PP) composites by dry sliding wear test. They reported that the both

the graphite filled PA66/PP composites and nano clay filled PA66/PP

composites exhibit a lower wear rate when compared to plain PA66/PP

51

composite. This wear resistance of the materials is due to the stability of the

transfer film on the counterface of the disc under dry sliding test.

Wang et al (2003) studied the dry sliding behavior of Nylon 1010

composite specimens prepared with MoS2 filler and with short carbon fiber as

the reinforcement. In the test MoS2 filler particles decomposed and its

compounds were found to increase the adhesion between the transfer film and

the counterface surface. The decomposed filler formed a thin, uniform and

continuous transfer film contributing to the increase in wear resistance of

nylon composites.

In most cases, carbon fiber proves better in this respect than the

more abrasive glass fiber. Carbon fiber is graphitized carbon with the

hexagonal planes of crystals aligned perpendicular to the fiber axis. The

lubricating function of the graphitized carbon was thought to be responsible

for the reduction of friction coefficient and wear rate as the composites slide

against the mating surface. Besides the lubricating function, carbon fiber also

enhances the thermal conductivity and mechanical properties of the polymer

matrix, which is believed to be beneficial to wear resistance as well. The

modification of tribological behavior of fiber-reinforced polymers by the

addition of filler material has been reported by many researchers. Most

studies on the influence of filler materials in the case of polymer composites

sliding against the metallic counterfaces, have reported a reduction of wear

rate and coefficient of friction. In addition to the higher mechanical strength

obtained due to the addition of fillers in polymeric composites, there is direct

cost reduction due to lesser consumption of resin material.

2.4.3 Effect due to Fiber Length and Fiber Orientation

Investigations have shown that the incorporation of fiber

reinforcement has improved the wear resistance and reduced the coefficient of

52

friction. Lancaster (1968) investigated the carbon and glass fibers reinforced

with various thermosetting and thermoplastic polymers under dry sliding

conditions. They reported that the randomly oriented fibers reduce both

coefficient of friction and the wear rates. It was also, reported that the

minimum wear is obtained when the fibers are normal to the sliding surface.

The carbon fiber reinforced polymers exhibit a lower wear resistance, a less

friction coefficient, a higher modulus of elasticity and greater flexural

strength. This wear and friction reduction may be due to applied load and

smoothing the surface of the steel counterface.

In the recent decades Short Fiber Reinforced Polymers (SFRP)

composites have grown rapidly in many engineering applications, particularly

automobile and mechanical engineering industry (Chou 1992). When

compared to continuous fiber composites, SFRP combine easier

processability with low manufacturing cost. Therefore short carbon fibers are

one of the most commonly used reinforcements for improving mechanical

and tribological performance of polymers.

Sung and Suh (1979) investigated the friction and wear behavior of

uniaxially oriented graphite fiber-epoxy, kevlar fiber-epoxy and biaxial glass

fiber-MoS2-polytetrafluoroethylene (PTFE) composites as a function of

varying fiber orientations with respect to the sliding direction. They reported

that the graphite fiber-epoxy composites showed minimum wear and friction

coefficients when the orientation of the fibers was normal to the sliding

surface. Also, kevlar-epoxy composites showed a minimum wear rate but the

friction coefficient was the highest when the fibers were oriented normal to

the surface and the sliding direction.

Xian and Zhang (2004) investigated dry sliding wear behavior of

short carbon fibers with solid lubricants such as graphite flakes and

poly(tetrafluoroethylene) powders reinforced into a poly(etherimide) matrix.

53

They stated that composites filled with equilibrium contents of solid

lubricants and short carbon fibers, ie., 10 vol % of each filler, exhibited a

lower wear rate and friction coefficient; conversely, the lower concentration

of solid lubricants adversely affect the wear resistance. During sliding,

continuous and effective friction films formed on the material pairs is the

reason for the improved tribological properties.

Lu et al (1993) investigated the dry sliding and abrasive wear

behavior of a unidirectional carbon-fiber reinforced glass matrix composite at

room temperature. The wear rate and friction coefficients were investigated

for three principal sliding directions relative to the fiber orientations. They

reported that the highest wear resistance and lowest friction coefficient were

observed in the anti parallel direction. It was noted that on both the composite

and counterparts, the wear rates decreases with an increase in hardness of the

counterpart material.

Chang (1982) investigated the friction and wear characteristics of

carbon-carbon composites for aircraft brake materials and the wear rates were

measured in terms of weight loss and thickness reduction. They reported that

the wear rates in terms of weight loss were always greater than those in terms

of thickness reduction over a wide range of braking conditions. This is

attributed to the oxidation of carbon beneath the porous friction surfaces. One

way of controlling rate step for oxidative weight loss is through the diffusion

of oxygen through pores. This has been proposed due to the excellent

concurrence between the activation energies for the oxidation of carbon and

for material loss on non-friction surfaces.

Tripaty and Furey (1993) investigated the tribological behavior of

unidirectional graphite-epoxy and carbon-PEEK (Poly (ether ether ketone))

54

composites in sliding contact. They reported that surface temperatures

increased with an increase of velocity; the coefficients of friction decreased

with an increase of sliding velocity and were significantly influenced by fiber

orientation. Also, the graphite-epoxy composites showed the minimum wear

at intermediate velocity; conversely the carbon-PEEK composites showed a

higher wear.

2.4.4 Effects due to the Bidirectional Composites

Suresha et al (2006) investigated the triblogical properties of glass-

epoxy (G-E) and carbon-epoxy (C-E) composites under the dry sliding

conditions. They reported that the C-E composite exhibit a lower wear loss

and co-efficient of friction against the hard steel disc when compared to the

G-E composite, since the carbon fibers act as a self lubricating material.

Bijwe et al (2002) experimented dry sliding wear study of three

different weaves (plain, twill and woven) glass fabric reinforced with the

polyetherimide (PEI) matrix composites and also another composite prepared

with PTFE and Cu fillers. They reported that plain weave glass/PEI enhanced

wear resistance and yielded minimum coefficient of friction when compared

to the other two composites. This is because of a very thin and uniformly

spread layer of back-transferred polymeric material, adhering very strongly to

the fabric. It was also noticed that the addition of fillers affect the wear

properties of the composites.

Gomes et al (2001) conducted the sliding experiments for

unidirectional PAN/resin Carbon Fiber Reinforced Composite (CFRC) pins

on two-directional rayon/resin CFRC discs with room temperature and

moderate speeds. They reported that the CFRC pin was subject to less wear

and moderate friction coefficients. Wear resistance strongly decreases with an

55

increasing sliding speed or test temperature. Also they reported that at higher

speeds, the disc was subjected to catastrophic failure level due to fatigue and

frictional heating effects result in extensive fiber matrix debonding and fiber

fracture.

Suresha et al (2010) investigated the friction and dry sliding wear

behavior of glass and carbon fabric reinforced vinyl ester composites. They

reported that the coefficient of friction and wear rate increased with an

increase in load and the sliding velocity depends on type of fabric

reinforcement and temperature at the interphase. Carbon fabric reinforced

vinyl ester showed a better wear resistance when compared to glass vinyl

ester composite. This is because a thin film formed on counterface appeared

to be effective in improving the tribological characteristics.

Zhang et al (2008) investigated the friction and wear properties of

CF reinforced phenolic composites using the ring-on-block tester. They

reported that both sliane coupling agent and HNO3 oxidation can help to

improve the friction and wear behaviour of CF reinforced phenolic

composite, while combined surface treatment is the most effective one to

decrease the friction coefficient and wear rate of the composite.

Vina et al (2008) investigated the wear behavior of glass fiber

fabric reinforced polyetherimide (PEI) composites under dry sliding

conditions with ambient temperature and for increased temperature up to the

200°C. They reported that the wear volume of the glass-PEI composites

decreased with the addition of glass fiber than the plain PET. It was also

noted that the wear volume of the glass-PEI composite also increased with an

increase in temperature. Even though for the temperature of 200°C, the wear

volume decreases. The reason is the contact point of composite pin reaches

higher temperature nearer to the glass transition temperature due to micro

structural variation in the material.

56

Joakim Schon (2004) investigated the friction study on bolted joints

(a large part of the load is transferred by friction) made of bidirectional

carbon fiber epoxy matrix composite by reciprocal sliding. They reported that

during testing, the coefficient of friction increased initially with a number of

cycles and after reaching a maximum, then slowly decreased. The reason for

this behavior is the wear debris is reattached to the composite surface during

wear and the surface is covered with a layer of wear debris.

Sliding friction and wear characteristics of three-dimensional (3-D)

braided carbon fabric reinforced epoxy resin (C3D/EP) composites were

investigated by Wan et al (2006) and the tests were performed for different

velocities and the applied loads. From the results, they reported that the

coefficient of friction and specific wear rate changed during running –in

period and reached a stable value at the steady wear stage. This is because the

fiber-matrix bonding is main reason for the reduction of wear rate and

coefficient of friction.

Viswanath et al (1993) investigated the influence of three different

matrix resins such as epoxy, polyester and modified phenolic on the sliding

wear of bidirectional glass woven roving reinforced polymer composites

under dry conditions. They reported that the glass/phenolic composites

exhibited the highest mechanical properties whereas the highest wear

resistance (minimum specific wear rate) was presented by glass/epoxy

composites. Further, they reported that the structural integrity of

glass/phenolic composites gave the lowest coefficient of friction at all sliding

velocities.

2.4.5 Effects due to the Bidirectional Composites with Filler Materials

The use of graphite as a filler material was known to improve the

mechanical and tribological properties of polymer matrix composites. The

57

mechanical and tribological properties of the particulate-filled bi-directional

carbon/glass fabric-reinforced epoxy composite material were evaluated by

Suresha et al [2006, 2007 and 2009]. They concluded that the incorporation of

particulate fillers improved the mechanical and tribological properties of

polymer composites.

Shivamurthy et al (2009) investigated the influence of particulate

filler such as SiO2 (3, 6 and 9 wt %) with the E-glass woven fabric-epoxy (G-E)

composites on mechanical and wear behaviors. They stated that the silica

content of 3 and 6 wt.% SiO2 particulate filled G-E composites exhibits good

performance in sliding wear resistance. Also, the improved mechanical

properties by the enhanced interlaminar shear strength due the addition of

SiO2 fillers on G-E composites were reported.

Suresha et al (2009) investigated the dry sliding wear and two-body

abrasive wear behavior of graphite filled and unfilled carbon fabric reinforced

epoxy (C-E) composites. The results of dry sliding wear tests revealed that for

increased load and sliding velocity, higher wear loss was recorded and the

graphite filled C-E composite exhibit lower wear rate. The reason behind this

development is the graphite surface film formed on the counterface which

was confirmed to be effective in improving wear characteristics of graphite

filled carbon-epoxy composites.

Kishore et al (2000) analyzed the influence of sliding speed and

load on the friction and wear behavior of glass-reinforced polymer composite

filled with either rubber or aluminium oxide particles. They reported that the

wear loss increases with an increase in load/speed. Even though the oxide –

filled composites showed minimum wear at lower loads; rubber-filled

composites showed minimum wear at higher loads.

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Suresha et al (2006) investigated the effect of inorganic fillers such

as SiC particles and graphite on the glass fabric reinforced epoxy composites

under dry sliding wear conditions. The results revealed that the graphite filled

glass-epoxy composites showed lower coefficient of friction; also the SiC

filled glass-epoxy composites exhibited a minimum wear resistance.

With reference to the literature survey, most of the above findings

are based on the unidirectional oriented or randomly oriented fiber reinforced

composites. Mody et al (1988) investigated the bi-directional fiber reinforced

composites and reported that the excellent wear resistance of the composites

was due to bi-directional fibers. Hence, the dry sliding wear behavior of bi-

directional carbon fiber reinforced epoxy matrix composites with various

wt% of SiC filler particulates have been considered for the present

investigation to develop the new concept materials.

2.5 ABRASIVE WEAR BEHAVIOR OF FIBER REINFORCED

POLYMER MATRIX COMPOSITES

Gates (1988) discussed the classification of abrasive wear such as

two-body abrasion and three-body abrasion. The two-body abrasion is more

severe than the three-body. Gates stated that the three-body abrasion was

equivalent to high-stress abrasion and is generally more severe than two-body

(low-stress) abrasion

2.5.1 Two-body Abrasive Wear Behavior

Wada and Uchiyama (1993) investigated the friction and wear

properties of Short-Fiber-Reinforced Chloroprene rubber (SFRR) composites

in the Longitudinal (L), Transverse (T) and Normal (N) direction oriented

polyamide fibers. The experiments were conducted at various sliding speeds

of rubbing against abrasive papers. They reported that the composites were

59

rubbed against the abrasive paper, the wear rates of the SFRR composites

decreased when compared to unreinforced chloroprene rubber.

Tewari and Bijwe (1993) investigated the abrasive wear behavior

of various composites of polyamide (nylon 6, 6) reinforced with increasing

amounts of carbon fiber against various abrasive papers under dry conditions.

They reported that combination of particulate filler (PTFE) and carbon fiber

proved to be very harmful to abrasive wear resistance. Load, abrading

particle size and fiber orientation were also observed to be important factors.

Cirino et al (1988) experimented the dry sliding and abrasive wear

behavior of various thermoset and thermo polymer composites and they

reported the following outcomes: a) the epoxy and PEEK matrices showed

the lower wear rate when filled with the carbon/aramid fibers than the unfilled

state. b) the lower specific wear rate was identified in the composites when its

fiber orientation was parallel.

Lhymn et al (1985) investigated the wear rate and friction

coefficient of short carbon/glass fiber reinforced plastics (PEEK, PPS, Nylon)

as a function of abrasive particle size, fiber orientation and sliding velocity.

Lhymn reported that the wear rate is sensitive to fiber orientation with respect

to sliding direction. The normal orientation of fiber to sliding direction exhibit

lower wear rate when compared to parallel and anti parallel orientation of the

fiber. Also, they stated the frictional force increased with an increase of

abrasive particle size.

Anand Chairman et al (2011) investigated the two-body abrasive

wear behavior of titanium carbide (TiC) filled glass fabric-epoxy (G-E)

composites under different sliding condition using the Pin-on-disc wear tester.

He reported that the addition of TiC particles with the G-E composite

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enhances the wear resistance. The wear loss of the composites was identified

due the applied load only.

El-Tayeb (2009) investigated the two-body abrasive wear behavior

of Sugarcane Fiber Reinforced polyester and synthetic R-glass fiber (GRP)

reinforced polyester composites using pin-on-ring wear test apparatus. The

test results revealed that chopped strand mat Sugarcane Fiber Reinforced

reinforced polyester consisting of fiber exhibit a good abrasion resistance

compared to GRP composites. This is due to the tendency of Sugarcane Fiber

Reinforced to bend easily under abrading conditions.

Harsha and Tewari (2003) investigated the two-body and three-

body abrasive wear behavior of various polyaryletherketone (PAEKs)

composites such as polyetheretherketone (PEEK), polyetherketone (PEK),

polyetherketoneketone (PEKK) with various fillers using a pin-on-disc

machine and a Rubber Wheel Abrasion Test (RWAT) rig. The results

revealed that for all PAEKs composites, specific wear rate of two-body

abrasion is greater than the three-body abrasion. The fillers such as PTFE and

graphite particles in PAEKs composites were found to be more harmful to its

wear performance. The reinforcement of glass fibers and carbon fibers with

the PAEKs composites enhances wear resistance.

Mohan et al (2010) investigated the effects of silicon carbide fillers

on two-body abrasive wear behavior of glass fabric-epoxy (G-E) composites.

They reported that increase of abrading distance increases the weal loss

linearly. The addition of SiC particles with the G-E composites increases

wear resistance. This is due to the incorporation of SiC particles, led to less

matrix and less fiber damage during the abrasion.

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Suresha and Shivakumar (2009) investigated the abrasive wear

behavior of glass and carbon fabric reinforced vinyl ester composites. They

reported that wear volume loss of all composites increased with an increase in

abrading distance and abrasive particle size. However, the specific wear rate

decreased with an increase of abrading distance and decrease of particle size.

It was also found that the carbon-vinyl ester composite exhibit a better

abrasion resistance when compared to glass-vinyl ester composites under

different loads and abrading distances.

Suresha et al (2010) studied the influence of graphite filler

additions on two-body abrasive wear behavior of compression moulded

carbon–epoxy (C–E) composites using pin-on-disc wear tester against the

different grades of SiC abrasive paper. They reported that the graphite filler in

C–E composite reduced the specific wear rate; also the wear volume loss

drops significantly with an increase in graphite content. In the graphite filled

C-E composite, filler-filler interaction and uniform distribution of the filler in

matrix enhances the wear resistance of the C-E composite.

Raju et al (2012) investigated the mechanical and two-body

abrasive wear behavior of silicon dioxide (SiO2) filled glass fabric reinforced

epoxy (G-E) composite. He reported that the addition of SiO2 particles with

the G-E composites enhances its wear performance and mechanical properties

of the composite. The SiO2 filled G-E composite exhibited a better abrasion

resistance when compared to the unfilled G-E composite under given speed

and load conditions. This is because of the brittle nature of glass fabric and

uniform distribution of SiO2 fillers.

Bijwe et al (2007) developed the five plain weave CF reinforced

Polyetherimide (PEI) composites, with CF contents in the steps of 10 vol% as

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a filler material and investigated the abrasive and mechanical behavior of the

composites. The result revealed that 65 vol. % of CF/PEI composites exhibit a

better wear resistance and improved mechanical properties such as tensile and

shear strength. The abrasive wear resistance of the composites by the

influence of fabric orientation with respect to the sliding plane and direction,

and the fiber orientation normal to the sliding plane showed an improved

trend when compared to parallel orientation of the CF fiber in the composites.

2.5.2 Three-body Abrasive Wear Behavior

Patnaik et al (2010) studied the three-body abrasive wear behavior

of random glass fiber-epoxy resin (RGF-Epoxy) composites filled with

Silicon Carbide (SiC), Alumina (Al2O3) and Pine Bark Dust (PBD) fillers.

The results revealed that addition of SiC filler with the RGF-Epoxy

composites reduces the mass loss and specific wear rate when compared to

alumina and pine bark dust filled RGF-Epoxy composites. Also, they reported

further wear mechanisms such as plastic deformation, pitting in the matrix,

micro-cutting, ploughing etc., on the composites.

Surface treatment of carbon fibers (Qin et al 2003) is commonly

used to improve the fiber–matrix adhesion, interfacial shear strength, etc.

However, literature reveals only a few studies which focus on the effect of

surface modification of filler on abrasive wear properties of fiber-reinforced

polymer composites (Cirino et al 1987). It was reported that silane coupling

agent promotes the interfacial adhesion and interfacial toughness between

glass fibers and polytetrafluoroethylene (PTFE) and also largely enhance the

tensile and tribological properties of glass–PTFE composites to a significant

effect (Cheng et al 2003). The whole phenomenon of abrasion was a

63

complicated matter influenced by different factors such as the properties of

materials coming into contact with each other and service conditions.

Friedrich (1993) investigated the abrasive wear behavior of dental

composites against the quartz abrasive with various fillers such as untreated

quartz, silane-treaded quartz filler and untreated glass-bead filler. They

reported the silane treated quartz filler influences composites and reduces the

wear rate when compared to the other composites

Harsha and Tewari (2003) investigated the effect of reinforcement

fibers, solid lubricants, mass of abrasives and load in polyaryletherketone

(PAEK) matrix under three- body abrasive wear conditions. The results

revealed that among the selected PAEKs the ketone/ether ratios played a

significant influence on three-body abrasive wear behavior at a higher load. It

was also found that an abrasive wear rate was higher in composites when

compared to the neat matrix at different loads. The abrasive wear rate of

composites increases with an increase of fiber content also carbon fiber

reinforced PEEK composite had a worst abrasive wear resistance when

compared to glass fiber reinforced PAEK composites. It was also observed

that the fillers such as PTFE and graphite particles were found to be

detrimental to wear performance.

Basavarajappa et al (2010) investigated the effect of SiC filler

material on three-body abrasive wear behavior of glass-epoxy composites

under the parameters of abrading distance, applied load and sliding speed.

They reported that the weight loss increases with an increase in load, sliding

speed and abrading distance; even though SiC filled glass-epoxy composite

exhibit a significant wear resistance by the loading of SiC when compared to

the unfilled glass-epoxy composites.

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Yousif et al (2012) studied the three-body abrasive wear behaviour

of Chopped strand mat Glass fiber Reinforced Polyester (CGRP) for three

principal orientations of the fibers, i.e. Parallel Orientation (P-O), Anti-

Parallel Orientation (AP-O) and Normal Orientation (N-O) under high stress

conditions. They reported that CGRP composite exhibited better wear

characteristic in P-O as opposed to in AP-O and N-O of fibers.

Chand et al (2000) investigated the three-body abrasive wear

behavior of short E-glass fiber reinforced polyester with and without the use

of filler. They used the Rubber wheel abrasion test apparatus and reported

that the abrasive wear rate increases with an increase of applied load and size

of abrasive particles. However wear rate was found to reduce with an increase

in sliding velocity. They further reported that wear resistance increases with

an increase in weight % of glass fiber reinforcement in the matrix and the

addition of calcium carbonate fillers. This is because high energy is required

to facilitate failure in glass fibers.

Suresha et al (2010) investigated the mechanical and three-body

abrasive wear behavior of carbon fabric reinforced epoxy (C-E) and silane-

treated graphite filled C-E (Gr-C-E) composites. They reported that the wear

volume was increases with an increase of abrading distance; also, specific

wear rate was decreased with abrading distance/load and depends on filler

loading. The presence of silane-treated graphite filler in C-E which showed a

promising trend was also reported.

Mohan et al (2011) stated the three body abrasive wear on glass

fabric-epoxy (G–E) composite incorporated with the tungsten (WC) and

tantalum niobium carbide (Ta/Nbc) powders. The results revealed that hard

carbide powders filled composites such as G–E–WC and G–E–Ta/Nbc

65

composites exhibit a lower wear volume loss and a lower specific wear rate

when compared to unfilled G–E composite.

Suresha and Chandramohan (2008) investigated the abrasive wear

behavior of Glass-vinyl ester (G-V) composites with the addition of SiC and

graphite fillers by rubber wheel abrasive wear tester. They reported that the

SiC filled G-V composite exhibits a better wear resistance when compared to

the graphite filled materials. This is because the hardness of the SiC particles

spread with the fiber matrix of the composite led to the stronger interface

bonding between glass fiber and the vinyl matrix.

Chand and Neogi (1998) investigated the low-stress abrasive wear

behavior of chopped-glass-fiber-reinforced polyester composites using a

rubber wheel abrasion tester. Silica sand particles of two different size ranges

were used and tests were conducted as a function of abrading distances. They

reported that the wear rate remains constant with the increasing sliding

distance on the composites.

Durand et al (1995) added ceramic particle such as Al2O3, TiC,

SiC, TiN, VC, TiO and ZrO as fillers with the polymer-based epoxy matrix

composite material the wear test. The results indicated that the composite

material containing the carbide particles, TiC and SiC, exhibit a higher wear

resistance when compared to the material containing the oxide particles, TiO,

Al2O3 and ZrO.

The three-body abrasion of SGF, C-E thermoset polymer

composites with and without particulate fillers were studied (Chand et al

1998, 2000, Suresha et al 2010). It was found that the fillers increase the

reinforcement content and also improved the abrasion resistance of the

66

composite. However, particulates/short fiber filled thermo plastic composite

showed deterioration of wear property (Harsha et al 2002), the three body

abrasion of particulate filled thermoplastic composite was studied and found

that increasing filler content worsened the wear property of the composite.

Although abrasive wear involving fiber reinforced polymer composite covers

a huge area in the literature: The wear process particularly involving micro

filler filled and fiber reinforced polymeric composite is still not well

understood. On the basis of the above literature studies, till date, no work was

carried out to study the effect of silane-treated SiC filler addition into carbon

fiber-reinforced epoxy matrix composite. The proper understanding of

abrasive behavior of unfilled and silane-treated SiC-filled C–E composite was

necessarily required for the end applications. Hence, in the current work, an

attempt has been made to study the two-body and three-body abrasive wear

behavior of silane-treated SiC-filled C–E composites.

2.6 AIM OF THE PRESENT STUDY

From the literature survey, it can be observed that many researchers

attempted to study role of fillers such as Al2O3, MOS2, Ag2S, CuS, SiO2,

TiO2, CaCO3, TiC, TiN, VC, TiO and ZrO, mica, graphite on the mechanical,

tribological and thermal behavior of polymer matrix composites. However,

the study of silane-treated SiC particulates as a filler material and its

performance on polymer matrix composites has not been extensively studied.

Also, bi-directional FRP composites have been widely used in all the fields

because of its enhanced load carrying capacity, improved wear resistance and

friction when compared to particulate filled/unfilled unidirectional FRP

composites. Thus, the present work aims to investigate the role of silane-

treated silicon carbide particulate filler on the mechanical and tribological

behavior of bi-directional silane treated carbon fabric reinforced-epoxy matrix

67

hybrid composites. With reference to the issues cited above, the present study

aims to

1. Evaluate the mechanical properties such as hardness, tensile

and flexural properties of unfilled and silane-treated SiC

particulates filled bi-directional silane-treated carbon fabric

reinforced-epoxy (C-E) hybrid composites.

2. Evaluate the thermo-mechanical behavior of unfilled and

silane- treated SiC particulates filled bi-directional silane-

treated carbon fabric reinforced epoxy hybrid composites.

3. Understand the influence of the various parameters such as

sliding distance, applied load and sliding velocity on friction

and dry sliding wear behavior of unfilled and silane-treated

SiC particulates filled bi-directional silane-treated carbon

fabric reinforced-epoxy hybrid composites.

4. Evaluate the influence of the abrading distance, abrasive paper

grit size and applied load on two-body abrasion and also to

study the influence of the parameters such as abrading distance

and applied load on three-body abrasive wear behavior of

unfilled and silane-treated SiC particulates filled bi-directional

silane-treated carbon fabric reinforced-epoxy hybrid

composites.