Detection of Impact Damage in Composite Structures Using High Speed FBG Interrogator

In the case of composite structures, low-velocity impact events can cause various types of damage that are mostly hidden inside the laminates or occur on the side opposite to the impact. Thus, damage cannot be easily detected by visual inspection or conventional NDT techniques. Moreover, if the damage occurs between the scheduled inspection periods, the possibilities of extensive damage or catastrophic failure can be increased. For these reasons, built-in NDT systems, such as the real-time impact monitoring system, are required in most composite structures for high reliability and ease of maintenance. In this paper, such an impact monitoring system, including impact location detection and damage assessment techniques, was studied for composite flat and stiffened panels. In order to acquire the impact-induced acoustic signals, four multiplexed fiber Bragg gratings (FBGs) and commercial high-speed FBG interrogator were used. In signal processing for the detection of impact locations and damage occurrences, neural networks and wavelet transforms were adopted. Finally, these algorithms were embodied using MATLAB and LabVIEW software to obtain a user-friendly interface.