Non destructive control for composite materials - Controllo non distruttivo di materiali compositi

It is well known that the most widespread technology in the shipbuilding sector, both for the construction of laminate products (single skin) and the construction of sandwich products, which are based on two reinforcement skins with a lightweight core in the middle, is called manual layup. Whereas this technique allows to cut the fi nished product cost, due to labour and to the energy consumption rate, it also lengthens the manufacturing process time and the fi nished products’ quality cannot be controlled (the resin content rate is related to the operator’s skill). Furthermore, as the various reinforcement layers bonding operation is carried out manually, it may cause air bubbles, which results in serious structural and aesthetical defects. To tackle these typical problems of the MLU technique, nowadays the Vacuum Infusion Process is often used, that is the vacuum infusion method. The use of new technologies such as VIP allows to obtain top quality fi berglass products, with few lay-up defects, which can be reproduced and constructed in a very short working time compared to the traditional lay-up process. Conversely, this technique involves higher construction costs, especially when larger parts are to be manufactured (use of autoclaves). There are several techniques for the mechanical properties control, as well as for the quality and the aesthetics of the product and the one which is suggested in this study is based on the Structure Healthy Monitoring procedures (SHM), in other words all those techniques which allow to control the structure life-cycle using non destructive methods (NDT). The Dynamic Damage Detection process (DDD), involves three diff erent steps: i) structure dynamic characteristics measurement , ii) assessment of a proper damage hazard rate, iii) prediction of the structure damage rate. This study focuses on the fi rst of these three working steps: the selected method is based on the use of the Scanning Laser Doppler Vibrometry, which allows to monitor the tested structure modal characteristics, without any contact. Such a method thus shows use potentials on larger composite structures such as, for example, modern yachts.