Damage growth monitoring for a bonding layer of the aircraft bonding structure

This study is about some of the results of the test performed for the purpose of developing the damage monitoring system with the advanced composite bonding structure applied to a next generation aircraft. Through the past researches, we succeeded in receiving hundreds of kHz of elastic waves (lamb waves) launched from PZT by using an optical fiber sensor bonded to or embedded in a specimen. Furthermore, by using an FBG optical fiber sensor embedded in the bonding interface of a CFRP coupon specimen or a structure element specimen with skin/stringer bonded structure or bonded to the surface of the specimen, the test results have been proven and the fact is verified that regarding the structure of composites, variations of elastic waves according to damage growth can be received with high accuracy. The authors also suggest it is possible to detect a damage, which is generated inside composites by calculating the elastic waves. For this study, we manufactured a structural element specimen where a small-diameter optical fiber sensor is embedded in the bonding interface, which is simulated a skin/stringer bonding structure of actual composite structures. We also developed the system, which is detecting elastic (lamb) wave up to 1MHz on our own and optimized it according to the corresponding specimen. Furthermore, an artificial damage is installed to critical area of the structural element specimen as a damage origin point. It is verified that our monitoring system can detect the variations of elastic waves accompanying the damage of 20mm² occurring and growing from the artificial damage by the applied cyclic load.