Structural health monitoring of composite wing structure during durability test S. Takeda a, * , Y. Aoki a , T. Ishikawa b , N. Takeda c , H. Kikukawa d a Institute of Aerospace Technology, Japan Aerospace Exploration Agency, 6-13-1 Osawa, Mitaka-shi, Tokyo 181-0015, Japan b Aviation Program Group, Japan Aerospace Exploration Agency, Japan c Graduate School of Frontier Sciences, The University of Tokyo, Japan d Department of Aeronautics, Kanazawa Institute of Technology, Japan Available online 19 January 2006 Abstract FBG (fiber Bragg grating) sensors were applied to durability tests of a composite wing structure in order to verify its health moni- toring capabilities for long-term use. The durability tests included drop-weight impact tests and two periodic fatigue tests based on the design service life of the aircraft. The seven FBG sensors were installed to the surface of the test panel for the monitoring of impact damages and fatigue tests. The impact damages were detected by using the spectrum change of the sensor output. The strain changes during the fatigue tests were measured by the wavelength shift of the sensor output. The damage evolutions in the test panel were also evaluated by using NDI (non-destructive inspection) technologies: AE (acoustic emission) sensors, an ultrasonic C-scan, and pulsed heat- ing thermography. Compared with results of the NDIs, the FBG sensors could output valuable information for monitoring the structural integrity of the composite wing structure. As a result, it was confirmed that FBG sensors have the capability for the long-term health monitoring of large-scale composite structures. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Health monitoring; FBG sensors; Non-destructive evaluation; Composite wing structures 1. Introduction The weight reduction of the airframe structure is one of the requirements for the development of high-efficiency air- planes. In recent years, the application of composite mate- rials have realized this goal, and, moreover, new technologies known as stitching, co-bonding, and RTM (resin transfer molding) have been proposed for the pro- duction of these composite structures. These successful technologies have been applied to composite wing struc- tures in a five-year research project supported by NEDO (New Energy and Industrial Technology Development Organization), Japan. The objectives of the program are to establish and develop the basic technologies for the design and manufacturing of an innovative light weight structure [1,2]. In the project, JAXA (Japan Aerospace Exploration Agency) conducted a durability test of a sub- component of a composite wing structure to verify the durability and damage tolerance of the structure. Another requirement related to the airframe structure is a diagnosis of structural integrity. Many NDI technologies have been contrived and developed for this objective. When in-flight monitoring is needed, the FBG sensors and AE sensors are promising sensing devices. The FBG sensors are a type of fiber-optic sensor and have the advan- tages of being lightweight, immune to electromagnetic interference, and multiplexing capability, while the AE sensors can monitor not only the fracture processes but also the source location of the captured AE events. On the other hand, ultrasonic C-scans and pulsed heating ther- mography are well known as almost matured NDI technol- ogies for the evaluation of damages in the composite structure. Though these technologies can visibly indicate 0263-8223/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2005.11.057 * Corresponding author. Tel.: +81 422 40 3569; fax: +81 422 40 3549. E-mail address: stakeda@chofu.jaxa.jp (S. Takeda). www.elsevier.com/locate/compstruct Composite Structures 79 (2007) 133–139