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s the boron fibre introduced by Talley (1959). Other examples for advanced fibres are carbon, aramid, silicon carbide, alumina, and sapphire. Glass fibres generally are not considered to be advanced fibres because of their low modulus compared with those of other advanced fibres. However glass fibre is an important engineering fibre because of its high specific strength and low cost [8].

2.1.2 Glass Fibres

Glass fibres are the most common of all reinforcing fibres for polymer matric composites [1]. Glass fibres are available in a variety of forms; E-glass, S-glass and S-2 glass are most common for structural application. When strength and high electrical resistivity are required then E-glass is used. E-glass is available as continuous filament, chopped staple, and random fibre mats suitable for most methods of resin impregnation and composite fabrication. S-glass is formerly developed for aircraft components and missile casings. It has the highest tensile strength of all fibres in use. The higher manufacturing charge and compositional difference make it most costly than E-glass. The lower cost version of S-glass is known as S-2 glass. S-2 glass is manufactured with less strict non-military specifications. But its tensile strength and modulus is similar to those

of S-glass [1]. S-2 glass is used in composite structural application. When high strength, modulus and stability are requires under extreme temperature and corrosive environment, S-2 glass is used [8].

S-glass is mainly available as roving and yarn and with a restricted range of surface treatments. S-glass fibres are being used in hybrid reinforcement systems in combination with graphite fibres and aramid fibres. In France a similar high strength and high modulus glass was developed and is known as R-glass [1].

The principal ingredient in all glass fibres is silica and so the chemical composition of E-glass and S-glass fibres is similar to the common soda lime glass. Oxides such as B2O3 and Al2O3 are added to modify the network structure of SiO2 and to improve the workability. The presence of Na2O and K2O is little in E and S-glass when compared to soda lime glass, due to this variation, E and S-glass exhibits better corrosion resistance to water as well as higher surface resistivity. The internal structure of glass fibres is a three dimensional, long network of silicon, oxygen and other atoms organized in a random fashion. Thus glass fibres are amorphous and isotropic [1].

2.1.3 Matrices

The matrix plays an insignificant role in the tensile-load carrying capacity of a composite structure. The selection of a matrix has a major effect on the inter-laminar shear as well as on in-plane shear properties of a composite material. For structures under bending loads, inter- laminar shear strength is an important design consideration, whereas the in-plane shear strength is important for structures under torsional loads. The role of the matrix in a fibre-reinforced composite is as follows [1]:

To transfer stress between the fibres

To provide a barrier against an adverse environment

To protect the surface of the fibres from mechanical abrasion

The matrix provides lateral support against the likelihood of fibre buckling under compression loading, thus inducing to some extend the compressive strength of the composite material. In