On the elastic stress transfer and longitudinal modulus of unidirectional multi-short-fiber composites

An analysis is presented on the elastic stress transfer and longitudinal modulus of unidirectional multi-short-fiber composites. The analysis involves a three-cylinder model consisting of fiber, matrix and composite medium. The fiber axial stress and the interface shear stress are derived as functions of the fiber axial position. The effects of fiber-aspect ratio, fiber-volume fraction, fiber-to-matrix modulus ratio and inter-fiber separation (or fiber end gap) on stress transfer are studied in detail. The influence of neighbouring fibers on stress transfer is considered in a global manner by including the effect of the composite medium. The significance of the influence is clearly shown by comparing the stress transfer in multi-short-fiber composites with that in single-short-fiber composites. The composite modulus can be expressed by a modified rule of mixtures equation by introducing a fiber-length factor. Then, the effects of fiber-aspect ratio, fiber-volume fraction, fiber-to-matrix modulus ratio and inter-fiber separation (or fiber end gap) on the fiber-length factor are investigated. Some interesting findings are obtained. Finally, the present theory is compared with several existing theories.