Overview

Metals, ceramics, glasses and polymers can be combined in materials that have unique properties on their own. Nature uses this principle in wood and bone; man applies it in a new family of supermaterials.

ANTHONY KELLY
"The Nature of Composite Materials,"
in Materials , W.H. Freeman and Co.,
San Francisco, 1967

5.1 Introduction

A common method of strengthening engineering materials is the development of a structure of one phase dispersed in another. For many metallic alloys, this is produced by specific heat treatments. An example is the formation of fine carbide particles in ferrite by tempering a hardened (martensite) steel, giving a usable combination of strength and toughness. Such a dispersion of one phase in another is an example of a composite material.

Composites are heterogeneous structural materials consisting of two or more distinct phases, which are bonded chemically or mechanically. They can be produced by appropriate thermal and mechanical treatment, such as the tempering of steels cited above. This type of composite is referred to as an in situ composite, and it usually has a fine structure. However, many composites are manufactured by mixing the individual components (phases) in a manner to bond them. An example is the embedding of glass fibers in epoxy to produce fiberglass. The structure of this type of composite is relatively coarse.

The properties of composites depend not only on the intrinsic properties of the dispersed component and those of the matrix, but also on the geometry (size and shape)...