Acoustic emission in carbon fibre composites

Acoustic emission analyses have been performed on carbon fibre-epoxy composites in order to correlate acoustic activity with well defined fracture processes. Different types of laminates were studied to discriminate the basic processes of fracture within the laminates. Test specimens were subjected to three-point flexural tests so as to separate fracture initiation and propagation. Acoustic emission signals were recorded by digital techniques for off-line analysis. Results show that during fracture initiation, high amplitude signals are correlated with fracture processes controlled by fibre rupture, and low amplitude signals with matrix fracture. For laminates characterized by major fracture propagation, acoustic emission is generated by the processes induced by the friction of the fracture surfaces created. This acoustic activity, associated with abnormally long duration and high amplitude signals, exceeds the emission generated by the fracture processes themselves.