On Failure Modes of Unidirectional Composites Under Compressive Loading

Experimental and theoretical studies are presented on failure modes of unidirectional composites subjected to compressive loading. Failure modes investigated include: fiber microbuckling, fiber-matrix debonding followed by microbuckling, interaction failure (transverse splitting) and fiber strength failure. Use of large scale, nearly perfect model composites is made in studying the various failure modes as well as the influence of fiber-matrix interface on the compressive strength. Approximate equations are presented for predicting the microbuckling failure of composites, compressive strength of composites with unbonded fibers as well as the interaction failure of unidirectional composites whereby the axial compressive strength is shown to be dependent on the transverse tensile strength of composites. A discussion is also presented on the various failure modes as applied to practical composites.