COMPOSITE MATERIALS CHARACTERIZATION BY ACOUSTIC EMISSION TECHNIQUE

Standard pencil lead break tests were carried out on CFRP laminates at the aim to characterize the composite materials behaviour from the acoustic emission point of view. Parameters like lay up, thickness and fibre orientation were varied in order to analyse their influence on the wave propagation. The generated waveforms were studied and the flexural mode was distinguished by the extensional one: the attention was put on the latter to correctly determine the sound wave velocity. From two to four sensors were positioned along the same line on the laminate at fixed distances between each other. This allowed the signal attenuation analysis too, performing pencil lead breaks against the panel along the same line of the sensors and comparing the signals, in terms of amplitude, recorded by each of the single sensor. The elastic modulus was predicted by the lamination theory and the related velocity was compared to what measured after experimental tests: a quite good agreement was found. At the final but not simple goal to individuate the exact number of sensors necessary to correctly locate the damage, the determined sound velocities were, then, used as input to verify the efficiency of the location method as a reliable tool to locate the source of an event. A quite good correspondence was found between the point of the pencil lead break against the panel and what shown by the AE system.