The physics and mechanics of brittle matrix composites

A major development in materials technology has been the synthesis of composites consisting of high strength particles, often in filamentary form dispersed in various solid matrices. This chapter discusses several composites in which the matrices, such as ceramics, glasses or intermetallic compounds, are brittle rather than ductile with elastic properties quite similar to those of the embedded fibers. Such fibers impart good tensile strength to the matrices, even in the presence of holes and notches. This characteristic is important because composite components generally need to be attached to other components, usually metals. At these attachments, stress concentrations arise, which dominate the design and reliability. Inelastic deformation at these sites is crucial. It alleviates the elastic stress concentration by locally redistributing stress. Such inelasticity is present in brittle matrix composites. In association with the inelastic deformation, various degradation processes occur that affect the useful life of these composites. The most severe degradation appears to occur subject to out-of-phase thermomechanical fatigue (TMF). In addition, creep and creep rupture also occur at high temperatures. The chapter also addresses the mechanisms of stress redistribution in these composites upon monotonic and cyclic loading, as well as the mechanics needed to characterize the notch. The basic phenomena that give rise to inelastic strains are matrix cracks and fiber failures subject to interfaces that debond and slide. © 1994, Academic Press, Inc.