An Introduction to Composite Materials

Composites are essentially materials comprising two or more distinct constituents, integrated into a single entity. An important aspect of composite theory concerns the properties that the material exhibits, expressed in terms of those of the constituents and the architecture of the integration. A case of interest is that of a two-constituent system in which one of them is just a void – possibly a vacuum, although more commonly a gas phase. Of course, voids have properties that are substantially different from those of constituents in conventional composites. For example, the stiffness will be effectively zero and the conductivity will tend to be very low. In practice, many materials contain at least some porosity, with the potential to affect certain properties, but in most cases it would not be considered appropriate to classify them as composites. However, very high porosity levels (say, >~30–40%) can justify treatment as a separate type of (composite) material. Sometimes the term ‘foam’ is used in such cases, although the word does carry connotations that would not necessarily apply to all highly porous materials. In this chapter, some composite theory approaches are applied to such materials and information is provided about their ‘microstructure’ (pore architecture), production and potential benefits.