Stress distribution along broken fibres in polymer-matrix composites

This paper presents a model for predicting the stress distribution along a broken fibre in a unidirectional composite. It is assumed that the matrix behaves in an elastic/perfectly-plastic manner, and that the interfacial shear strength is not lower than the matrix shear yield stress. Although ‘good’ interface bonding is assumed, the present analysis suggests that interface debonding may occur as a result of local matrix shear failure, resulting in the well-known splitting phenomenon observed in tensile tests. Along the debonded length, a decreasing interfacial shear stress is derived from Poisson contractions and Coulomb friction. The debond is followed by a matrix yielding zone, where the interfacial shear stress is assumed to be equal to the matrix shear yield stress. There is, finally, an elastic zone, where the interfacial shear stress follows a classical exponential law. The present model is in good agreement with a 3D finite-element model.