AbstractThe longitudinal strengths of unidirectional discontinuous fiber composites have been calculated based on the concept of perturbation effect and the distortional energy criterion, utilizing the finite‐element method. The theoretical results thus obtained are compared with the experimental data as well as the results of shear lag analysis for tungsten‐copper, boron‐aluminum, glass‐epoxy and boron‐epoxy composites. Based on the Jackson‐Cratchley equations, modified for discontinuous fibers, a formula is also proposed for calculating the strengths of randomly oriented discontinuous fiber composites. The results calculated from this formula are compared with the experimental data for aluminum oxide‐aluminum‐silicon and glass