Toughness characterization and acoustic emission monitoring of a 2-D carbon/carbon composite

The fracture behavior of carbon/carbon composites is mainly governed by the activation of multiple matrix cracking, shear band formation, fiber debond ing and fiber pull out, promoting the stress redistribution and offering a kind of "stress shielding effect" against crack propagation. In order to un derstand these effects and quantify the evolution of different damage mecha nisms in time, experiments have been conducted on compact tension (CT) test coupons, accompanied by continuous acoustic emission (AE) monitoring. Then , fracture mechanics analysis was applied on the experimental results and a signal pattern recognition classification process was developed for the AE data, supported by extensive microscopical examination and systematic ultr asonic inspection. Correlation between clusters, resulting from the classif ication algorithm of AE data, and damage mechanisms activated by load incre ase during the CT experiment was accomplished, using classification algorit hm parameters. A relation between the felicity ratio and the effective crac k length was introduced and the multiple matrix cracking resulting by the s hear failure of carbon matrix was found to act as the dominant stress redis tribution mechanism. (C) 2001 Elsevier Science Ltd. All rights reserved.