NONSELF-SIMILAR FIBER FRACTURE IN UNIDIRECTIONAL COMPOSITES

In unidirectional composites containing an initial notch or crack, the maximum stress concentration occurs at the notch along the notch plane. If the fiber failure is governed by maximum tensile stress, the fiber breaks and hence the notch extension should occur in a self-similar fashion. However, experiments show that the fibers break ahead of the notch tip, in many cases away from the original notch plane. An analytical model is developed for the determination of the stresses and displacements in a unidirectional composite containing a rectilinear notch along with some notch tip off-axis fiber breaks. The model is based on the so-called classical shear-lag theory in which the axial load carrying capacity of the matrix is neglected. The results show that the off-axis fiber fracture generally reduces the stress concentration along the original notch plane, and has a stabilizing effect on notch extension.