OXIDATION AND FRACTURE OF A WOVEN 2D CARBON-CARBON COMPOSITE

Measurements were made of flexural strength and dynamic elastic modulus of a woven, 2D carbon-carbon composite before and after oxidation in flowing, dry air. The microstructure and fracture surfaces were examined using optical and scanning electron microscopy. Oxidation preferentially attacks the fibre/matrix interfaces and weakens fibre bundles. The unoxidised material fails catastrophically by delamination cracking between plies and at bundle/bundle interfaces within plies. As oxidation progresses, failure becomes a multistep process with less delamination cracking and more cross-bundle cracking. This change of mode of failure with oxidation is attributed to more severe attack within bundles than at bundle/bundle interfaces. For a weight loss on oxidation of 10%, the reduction in elastic modulus and flexural strength was 30% and 50% respectively.