Micromechanics of nanocomposites

This chapter reviews recent studies of the mechanical properties of a wide range of nanocomposites, attempting to determine whether they are predictable by micromechanics models and mechanisms of the classical composite materials theory. It focuses on three property categories, namely, the strength (ultimate stress), stiffness (Young’s modulus), and toughness (fracture energy). For each category, the existing models of particulate and discontinuous composites are presented and discussed in terms of either their direct applicability to nanosize reinforcement or of the need for modified and alternative models. As the empirical values fall significantly below the predicted ones, with the exception of fracture toughness, it is concluded that micromechanics models and mechanisms fail to predict the mechanical properties of nanocomposites, which is attributed to the 3-fold scale difference between the nano and microdimensions, which cannot be reconciled. Instead, nanomechanics and nanomechanisms ought to be considered, which are related to interactions between the reinforcement and the polymer matrix on a molecular level.