The effect of intermediate graphitization on the mechanical and fracture behavior of 2-D C/C composites

Abstract

Impregnation and recarbonization effectiveness during the processing of carbon-carbon composites is largely enhanced by subjecting them to intermediate graphitization cycles. The effect of an intermediate graphitization cycle on the fracture toughness of a 2-D C/C composite has been investigated. Two materials have been considered. Both composites are reinforced with plain woven fabrics of carbon yarns, and their matrices are derived from the same resin. The only difference is that one of the composites has undergone an extra intermediate graphitization cycle. Flexural tests were conducted on multiple geometrically identical, un-notched and notched specimens of each composite in the translaminar and crosslaminar directions. The current study reveals that an intermediate graphitization has increased the fracture toughness of the C/C composite by about one fold, as measured by both the critical energy release rate at the onset of crack extension, GP ic , and the critical value of the J integral, J ic . This is accompanied by about a 25% loss in the translaminar flexural strength and a 25% decrease in the translaminar stiffness. A considerable decrease in the notch sensitivity of the C/C composite under investigation is also observed. The increase in the fracture toughness due to the intermediate graphitization of the C/C composite is also manifested in a more diffusive fracture path. The intermediate graphitization has also decreased the crosslaminar flexural strength by about 23% and the crosslaminar flexural modulus by about 15%.