Stiffness changes in unidirectional composites caused by crack systems

This paper is concerned with the development of constitutive equations for fibrous composites which contain a family of longitudinal slit cracks. The general theory in which the crack length is of the same order as the fiber diameter gives rise to a three-phase model. When the fiber diameter is much smaller than the crack length, we obtain the associated two-phase model. Detailed numerical results are given for selected systems.