CHAPTER 2 LITERATURE REVIEW - 2.pdf¢ incorporation of fibers (e.g., glass or carbon) or...
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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
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.
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
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
(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
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
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
Fu et al (2000) investigated t