Analysis of acoustic emission signals produced by different carbon fibre reinforced plastic laminates

Standard pencil lead break tests were carried out on unidirectional and symmetric laminates at the most important aim to investigate about the acoustic emission behaviour of the composite materials. Parameters like stacking sequence, thickness and fibre orientation were varied to verify their influence on the acoustic waveform generated by the standard pencil lead break. The extensional mode of propagation was analysed and the related velocity, Ce, was, first, measured from the difference in arrival time of the signal between two successive sensors located on the surface of the unidirectional panels at fixed distances. The data collected were used to find the four elastic constants characterizing the in-plane behaviour of the basic lamina. From them, the prediction of Ce for two symmetric laminates, namely [0, 90]3s and [03, 903]s, was attempted by lamination theory. To validate the theoretical predictions, additional experimental tests on different architectures were performed and the experimental values were compared with the theory. A quite general good agreement was found.