Why are reinforcement made in thin fibre form?

There are various reasons because of which the reinforcement is made in thin fibre form. These reasons are given below.

a) An important experimental study by Leonardo da Vinci on the tensile strength of iron wires of various lengths (see references in [2, 3]) is well known to us. In this study it was revealed that the wires of same diameter with shorter length showed higher tensile strength than those with longer lengths. The reason for this is the fact that the number of flaws in a shorter length of wire is small as compared longer length. Further, it is well known that the strength of a bulk material is very less than the strength of the same material in wire form.

The same fact has been explored in the composites with reinforcement in fibre form. As the fibres are made of thin diameter, the inherent flaws in the material decrease. Hence, the strength of the fibre increases as the fibre diameter decreases. This kind of experimental study has revealed the similar results [2, 3]. This has been shown in Figure 1.5 qualitatively.

b) The quality of load transfer between fibre and matrix depends upon the surface area between fibre and matrix. If the surface area between fibre and matrix is more, better is the load transfer. It can be shown that for given volume of fibres in a composite, the surface area between fibre and matrix increases if the fibre diameter decreases.