An Introduction to Composite Materials

There has been a prodigious level of interest in graphene over recent decades, and also in (the closely related) carbon nanotubes (CNTs). This has included quite a strong focus on their mechanical properties, with various claims in particular being made about high strength levels, which relate to their extremely fine scale. Since the scope for their usage in isolation is relatively limited, at least in terms of exploitation of high strength levels, a lot of attention has been directed towards the production and use of composite materials containing them as reinforcement. Unfortunately, most of the hopes originally expressed have not been fulfilled. In fact, the mechanical properties of such composites have in all cases been inferior to those of conventional carbon fibre composites. This is partly due to severe difficulties in manufacturing composites with relatively high levels of well-dispersed, well-aligned reinforcement. However, this is not the only problem, since many of the original expectations were based on incomplete understanding of the issues involved in defining the strength of a material, with particular reference to the role of toughness. These CNT-reinforced composites tend to have a low toughness, as a direct consequence of their very fine scale. In this chapter, the issue of scale-related effects is first addressed in general terms, followed by information about some specifics of using fine-scale reinforcement (particularly CNTs).