Effect of air oxidation at 873 K on the mechanical properties of a carbon-carbon composite

Abstract

A carbon-carbon composite, composed of semi-random chopped PAN fibers in a resin char and CVD carbon matrix, was oxidized in air at 873 K to burn-offs up to 55%. Composite reactivity increased with increasing burn-off up to about 10% and thereafter remained constant at 1.5%/h. Oxidation had a catastrophic effect on mechanical properties. For example, at 20% burn-off, Young's modulus, flexural strength, work-of-fracture, and fracture toughness were reduced by: 75, 64, 57 and 61%, respectively. Decrease in flexural strength is attributed primarily to a decrease in fracture toughness rather than an increase in flaw size.