Strain concentration factors for fibers and matrix in unidirectional composites

One of the methods of calculating the stress disturbances due to broken fibers in unidirectional composites is the so-called shear lag analysis. This method has been developed with the approximation that only the fibers carry the applied stress, not the matrix, and that the matrix acts only to transfer stress to the fibers. As a consequences of this approximation, the application of the method has been limited only to composites in which matrix stiffness is low in comparison with that of the fibers, and the volume fraction of fibers is high. In the present work, the ordinary shear lag analysis was modified to introduce the influence of the matrix stiffness. In this modified method, the tensile stress concentration in the fibers and matrix adjacent to cut fibers and matrix and shear stresses at the interface between fibers and matrix were estimated. The influence of interfacial debonding on the strain concentration was also studied.