On the use of acoustic emission for damage mode identification in the case of ceramic matrix composites subjected to compact tension test

Damage mechanisms in Carbon/Carbon composites consist of multiple matrix cracking, fibre debonding, pull out and shear band formation, promoting the stress redistribution and offering a kind of 'stress shielding effect' against damage propagation. In order to understand these effects and the evolution of the different damage mechanisms in time, experiments have been conducted on compact tension (CT) test coupons accompanied with continuous Acoustic Emission (AE) monitoring. Then, fracture mechanics analysis was applied on the experimental results and a pattern recognition classification process developed for the Acoustic Emission data Correlation between clusters, resulting from the classification algorithm of AE data, and damage mechanisms activated by load increase during the CT experiment was accomplished, using algorithm parameters. A relation between Felicity Ratio (FR) and effective crack length parameters was introduced. Multiple matrix cracking was found to act as the dominant stress redistribution mechanism.