Buckling behavior monitoring of composite wing box model using fiber Bragg grating sensor system

Advanced composites are being extensively used for aerospace structures due to the high stiffness to weight and high strength to weight ratios. Measuring internal strains of composite structures is of great interest with respect to the structural integrity of aerospace structures. A large number of sensors are required for large-scale structures such as aircraft. Fiber Bragg grating (FBG) sensor system based on the wavelength division multiplexing (WDM) technology offers a versatile and powerful one for strain monitoring of large structures due to the advantage of multiplexing capability. In this paper, we present an improved FBG sensor system using a wavelength-swept fiber laser (WSFL). The WSFL provides unique and powerful output characteristics useful for a large number of sensor interrogations without any other expensive optic devices such as optical switches. As a practical application of aircraft structures, we demonstrate 24 FBG sensors were used to monitor strains of the smart composite wing box model in the bending test. 3 sensor lines are embedded into upper skin and 1 sensor line is embedded into front spar of composite wing box. Each sensor line has 6 FBG for the strain sensing and 1 reference FBG for temperature compensation. Experimental results are compared with finite element analytical results. The structural bending behavior of composite wing box monitored by FBG sensors shows an almost same tendency with the analytical result. All strain data can be real-timely visualized and saved in PC.