Influence of fibre-matrix interface on the fracture behaviour of carbon-carbon composites

This paper studies the fracture behaviour of unidirectional carbon fibre reinforced carbon matrix composites and its relation with the type of fibre-matrix interface developed in the composite. Model unidirectional carbon-carbon composites were prepared using the same type of fibre and different pitches as matrix precursors. These included both commercial pitches and synthesized in the laboratory ones. The chemical composition of the matrix precursor determined the type of microstructure developed in the composite, this microstructure seems to govern the fibre-matrix bonding and in turn controls the fracture behaviour of the composite. In general, a matrix texture of mosaic (small size) seems to yield a good fibre-matrix bonding, making the materials to have higher interlaminar shear strength but having at the same time brittle fracture behaviour. On the other hand, composites where larger textures were developed in the matrix seem to have a poorer fibre-matrix bonding. This made the composites to have lower strength, but it allowed debonding of fibre and matrix during fracture. As a result, these materials showed pseudo-plastic failure behaviour. Other examples of both types of fracture behaviour associated with the change in microstructure and fibre-matrix interface are discussed.