Characteristics of Composites

This chapter reviews the essential differences of composites structural behavior from the more traditional metallic materials. Advanced polymeric composite material systems consist of fibers of high specific strength and stiffness embedded in a resin matrix of significantly lower stiffness and strength. In general, the discrepancy between the fiber and matrix stiffnesses is very significant for most fiber‐reinforced composite materials. It is well known that these fiber‐matrix stiffness discrepancies are difficult to model for an individual ply, and result in increased analytical difficulties of composite structures compared to the analysis of metallic structures. In contrast to metals, fiber‐direction composite failure prediction is in most cases performed using design strength values expressed as strains, both for in‐plane and flexural loading. The complete allowables database for fiber‐direction strengths is generally based on a failure strain methodology.