Non-axisymmetric matrix cracking and interface debonding in unidirectional brittle matrix composites

A discrete fiber model is developed in this paper and applied to study the problem of nonaxisymmetric matrix cracking and interface debonding in unidirectional brittle-matrix fiber-reinforced composite materials subjected to an axial tensile load in the fiber direction. In this model, it is assumed that the interface debond remains open. Considering the non-axisymmetry of the matrix crack and interface debond, a three-dimensional stress analysis is introduced into the above model. The variational approach based on the principle of minimum potential energy is employed to obtain the numerical results for stress and displacement fields. On the basis of Irwin-Kies compliance calibration formulation, the strain energy release rates associated with the matrix crack and the interface debond are calculated. The competition between these two modes is then assessed by comparing the corresponding toughnesses. It is shown that the magnitude of the toughness of the fiber/matrix interface plays a predominant role on the debond initiation and extension. The stabilities of the debond and the matrix crack extension are investigated. (C) Elsevier, Paris.