Debonding Detection in CFRP Bonded Structures Using Ultrasonic Waves Received by Optical Fiber Sensors

Carbon fiber reinforced plastic (CFRP) laminates have increasingly become popular materials for airplane structures. Since CFRP laminates have difficulties in joining with bolts or rivets, bonded structures with adhesive are more suitable to CFRP structures. However, bonded composite structures have a possibility of introducing debonding in the bonded line, which is a critical damage to the structures. Thus, detection of debonding is required for maintenance of airplanes. This paper presents a system to detect the debonding progress in skin/stringer structures in a wing box of airplanes. This system uses piezoelectric tranducers (PZTs) to input controlled ultrasonic waves to the structures and fiber Bragg grating (FBG) sensors to receive the propagated waves. To evaluate the debonding precisely, two sensors are attached to the top and bottom surfaces of the skin/stringer structure. Comparison of received waves between these two sensors provides an effective method to determine the condition of the structures. The applicability of this proposed system to the debonding detection was demonstrated by experimental studies. To investigate the influence of the debonding, a perfectly bonded specimen and a specimen with debonding were prepared for demonstration of this system. The results showed that the wave propagation path and received waveform were affected by the debonding. In particular, the maximum amplitude ratio and the arrival time difference were found to be important parameters to evaluate the debonding progress quantitatively. _____________ Kazuki Natori, YOJI OKABE, NOBUO TAKEDA, Dept. of Aeronautics and Astronautics, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan TOSHIMICHI OGISU, Fuji Heavy Industries Ltd, Aerospace Company, Engineering & Development Center, Research and Laboratories Dept SEIJI KOJIMA, Photonics Research & Development Center, Hitachi Cable, Ltd