Delamination, Fibre Bridging and Toughness of Ceramic Matrix Composites

Delamination cracks in long-fibre reinforced ceramic matrix composites are found to be bridged by fibres which span the crack wake at a shallow angle. The in situ observation of bridging fibres reveals that these are subject to considerable tensile forces, giving rise to a substantial crack closure force. The overall crack closure force is determined by the number of bridging fibres, steadily reduced by fibre failure caused by high bending moments at the root of each fibre. This leads to a model for crack closing forces combining simple mechanics and Weibull statistics. The model relates these forces to the properties of fibres, matrix and their interface.