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Transcript of CHAPTER 2 LITERATURE REVIEW - 2.pdf¢  incorporation of fibers (e.g., glass or carbon) or...

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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.

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    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

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    (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

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    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 t