ANALYSIS OF ACOUSTIC EMISSION SIGNALS PRODUCED BY DIFFERENT CARBON FIBRE REINFORCED PLASTIC LAMINATES

The advantage of the acoustic emission technique consists in the possibility to investigate about the material behaviour under loading in real time, without any contact, and to know the exact location of the eventual failure without damaging the structure. The AE system allows to analyse a large number of information about the phenomenon since the very big number of potential parameters offered. Each parameter can be useful for the comprehension of the damage phenomenon but it can be influenced by a large number of factors [1] not simple to distinguish one from the other. The problem is that each kind of damage is related to a different acoustic wave form and propagation [1]. The discussed problems are amplified when the acoustic emission technique is used on composite materials instead of on classic homogeneous ones. In this case in fact, the signal is influenced by the fibre presence too and the correlation of the very different failure modes to the acoustic signals recorded is, so, very difficult. A very important aspect is represented by the necessity to investigate about the phenomenon without damaging the structure [2]. While a big number of studies [3, 4] were carried out at the aim to verify the influence of parameters like fibre orientations, panel thickness and lay up, on the acoustic emission response of these materials under mechanical loads, the main scope of the present research is to characterise the composites acoustic behaviour, independently of the specific load applied and the damage occurred. Pencil lead breaks were performed against CFRP laminates, different in lay up and thickness. From two to four sensors were opportunely positioned on the panels at the aim to record the generated signal. The latter was then analysed in terms of amplitude and wave form and the influence of the varied parameters on the signal propagation, was verified. The influence of the fibre orientation and the stacking sequence respect to the sensor position, was studied too. Two different methods, experimental and theory, for the sound speed evaluation were compared and the results were used as input for the location analysis. A quite good agreement was found.