I Fiber Microbuc kling' A two-dimensional mechanicai model is presented to predict the compressive strength of unidirectional fiber composites using technical beam theory and classical elasticity. First, a single fiber resting on a matrix half-plane is considered. Next, a more elaborate analysis of a uniformly laminated, unidirectional fiber composite halfplane is presented. The model configuration incorporates a free edge which introduces a buckling mode that originates at the free edge and decays into the interior of the half-plane. It is demonstrated that for composites of low volume fraction ( A problem that has received much attention but moderate success is the prediction of compressive strength of fiber composites. Dow and Gruntfest (1960) were apparently the first to identify fiber buckling as a viable mode of compressive failure in composites. Their work was followed by that of Fried and Kaminetsky (1964) and Leventz (1964), who addressed. experimentally and theoretically the question of compressive strength. In these investigations, an empirical factor was used to o b t d~ a ccrrda:im between the experimentally and theoretically predicted values of compressive strength. In 1965, Rosen (1965) presented an analysis addressing the question of microbuckling which was devoid of any empiricism and laid the foundation for much of the work that was to follow. With a few exceptions, noted later, the analytical research work carried out in the past 20 years is based on the model by Rosen (1965). Due to lack of space and because an excpllent literature survey on fiber microbuckling exists @quart (1985)), a discussion of the various contributions that have enhanced our understanding of microbuckling will be omitted here. Instead, the discussion will be limited to those aspects that are fundamental in clarifying the state-of-the-art of the subject. The interested reader is referred to the references at the end of this chapter and the review by Shuart (1985). in particular, for a complete and up-to-date account.The Rosen (1965) model for microbuckling addresses the problem of fiber buckling in glass fiber/epoxy laminates