Structural Health Monitoring of composite pressure vessels using multiple damage indicators

Composite structures have been adopting increasingly in a variety of applications thanks to their high strength to weight ratio. Among them, bilayered (aluminum-carbon fiber) laminates are thoroughly exploited in space domain to ensure safety with lower mass possible. However they show complex inherent mechanics due to the interlaminar interation and discontinuity at the different material inteface. Major concern is about impact (e.g.: due to spce debris) induced damage consisting mainly in through shickness delamination and metal to composite disbonding. This paper deals with the latter phenomenon, approached in view of structural health montioring by ultrasound. A first experimental campaign is carried out to characterize guided ultrasonic waves travelling into the struture. Then, a numerical model based on finite element approach is validated and adopted to simulate damage. Finally, signal processing techniques are employed to find out wave features sensitive to flaw occurence at the interface level. The results shows a good agreement between numerical and experimental measurements. in addition, different frequencies of interrogation show a slightly different interaction with the emerging defects. Finally, signal processing techniques demonstrate that several damage indicators seems suitable for this application, enabling such a multi-parameter approach to improve detectability. Data can be stored to fatigue record and be used to warn the occurrence of a damage at any time looking into different parameters simoultaneously.