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Fibers reinforcements are important as they provide the desired functionalities as per the application requirement and transfer the strength to the matrix constituent by altering the properties of composites as per the requirements. The glass fibers are the earliest known fibers used to reinforce materials. Later, the ceramic and metal fibers were discovered and utilized to prepare stiffer composites. However, the fibers also suffer from certain limitations. Generally, the performance of fiber reinforcement is judged by its material, length, shape/orientation and the mechanical properties of the matrix. The strength of composite is highest at it’s longitudinal alignment, and so even a slightest shift in the angle of loading can reduce the strength of the overall composite material.

Figure 2.5 Types of reinforcements in composites.

In a 2-D composite, the strength remains only one-third to the strength of a unidirectional fiber-stressed in the direction of fibers, however, for a 3-D composite, less than one-fifth of the strength is obtained [17]. The fiber composites can be either continuous or short fibers. It is generally observed that the continuous fibers exhibit better orientation in matrix. The aspect ratio (length/diameter) of fibers is very high and so they can be processed easily using continuous process. Due to their high strengths and low densities, the fiber’s length greatly affects the mechanical properties and processing of composites. Also with the proper orientation of shorter fibers in composites comprising of glass, the multi-purpose fibers can be processed with higher strength. Filament winding process utilizes the continuous fiber constituent of a composite [18]. The short-length fibers are comparatively cheaper but are less efficient when incorporated by the open moulding process. The solid fibers are mostly used for their easy handling and production. However, hollow fibers and non-conventional shapes can improve the mechanical qualities of the composites. The high aspect ratio of fiber induces great strength in the composite due to minimization of surface of surface defects. Organic and inorganic fibers can also be used as reinforcement in composite materials. Organic fibers own low density, flexibility, and elasticity while, the inorganic fibers displays better modulus, thermal stability and superior rigidity in comparison to the organic fibers [19]. The frequently used fibers includes the fibers made of glass, silicon carbide, aluminina, metal, graphite, boron, aramid and multiphase. These fibers are discussed in detail as follows: