Impact damage detection for composite fuselage panel using distributed strain sensing based on fiber optic Rayleigh back-scattering

This paper presents the application of distributed fiber optic strain sensing to commercial aircraft composite fuselage panels for load monitoring and impact detection. This work is part of the EU SARISTU project aimed at enhancing the technology of Smart Intelligent Aircraft Structures. One aspect of Smart Intelligent Aircraft Structures is applying Structural Health Monitoring (SHM) using Fiber Optic Sensors (FOSs) [1]. Such SHM systems should prove extremely important in composite-made aircraft structure, where conventional inspection methods of critical structural components are time consuming and hindered by limited accessibility. Optical fibers are quite flexible and tolerant to environmental conditions and electromagnetic interferences. In addition, their small diameter allows them to be easily embedded within or externally bonded on large composite structural components, such as wings or fuselage skins, at relatively low cost. Rayleigh backscattering distributed strain sensing [2, 3, 4] is a new and very effective technique for high spatial resolution (millimeters) strain/temperature measurements. It uses coherent techniques to record the optical magnitude and phase of the Rayleigh backscattering, originating from the random refractive index variations of the amorphous glass. This sensing concept was applied to a typical aircraft fuselages panel with Omega shaped stringers, tested under compression. A barely-visible impact was introduced at a critical stringer to skin joint, since such damage may have a major influence on the residual strength of such structure. The Rayleigh backscattering sensing concept successfully detected the frozen change in strain, originating from the impact, i.e., it discovered an impact-induced damage without the need to capture the impact event. This should pave the way for real time damage detection of large scale composite structures.