Thick layer equally oriented effect on acoustic emission behaviour of carbon-fibre-reinforced-plastic laminates

Pencil lead break tests were carried out on symmetric 0/90 laminates, and the results in terms of extensional velocity and amplitude were analysed. The aim was to investigate about the influence of the stacking sequence and direction on the acoustic response of the materials. The wave velocity was measured from the difference in arrival time of the signal between two successive Acoustic Emission sensors, and predicted by lamination theory in the different test conditions analysed. A general agreement was found between theory and experiments, even if the differences found in correspondence of some orientation confirmed previous results, indicating an influence of layer thickness on the wave velocity. The data were used to verify the possibility to correctly locate the acoustic source through the location analysis, yielding satisfactory results. A simple, exponential law was able to predict the dependence of signal amplitude on the distance from the source. Indeed, attenuation was scarcely affected by fibre orientation and lay-up. This suggests that a method based on attenuation, rather than arrival time, could be useful for source location in composite laminates.