Acoustical studies of damage mechanisms in carbon-carbon during first carbonization

Acoustical studies of damage mechanisms in carbon-carbon during first carbonization are reported. Normal and anomalous temperature profiles are treated to investigate the damage mechanisms. Small plates of carbon-carbon were suspended in a small research autoclave with acoustic emission (AE) sensors, thermocouples, and a gas-flow meter to monitor the state of the materials during the 25°C to 700°C temperature ramp. A so-called normal carbonization is characterized by the evolution of an open network of fine cracks which allows the escape of gases created during the chemical alterations of the matrix. The associated damage is therefore desirable and constitutes no threat to the material. This is contrasted with the damage resulting from anomalous carbonization runs which produce large localized pores and cracks just short of delamination. This damage is undesirable and is associated with significantly different AE signatures. Therefore the use of AE sensors is emerging as a useful tool to recognize the possible onset of undesirable damage to the material as it is undergoing carbonization