Feasibility studies on active damage detection for CFRP aircraft bonding structures

This paper presents a part of the feasibility study for employing a damage monitoring system using a PZT actuator/FBG sensor. The goal of this research is to improve the present safety level of aircrafts by ensuring structural integrity and reducing maintenance/operation costs of advanced composite materials that will be employed for the primary structures of the new generation aircraft. Our novel sensor system employing a PZT actuator and an FBG optical fiber sensor can detect several types of damage, such as delamination and debonding, which are expected to occur in the highly efficient bonding structures of an aircraft wing box when the main/tail wing section is designed using composite materials. In this system, elastic waves will be transmitted into the structure by PZT actuators and received by small-diameter FBG optical fiber sensors that are embedded in the critical section of the primary structure of an aircraft. The onset and growth of damage can be detected with a very high accuracy through the change in the received elastic waves. In this study, a conceptual design was implemented in order to employ the novel system. We also selected the optimum application candidate area in order to verify the effects of the system. Further, the investigation and experiment on the novel sensor system that uses a bonded PZT actuator and an FBG sensor was carried out, and the basic damage detection technique was established based on the experimental results of the received elastic wave. Furthermore, compressive tests were carried out using the coupon specimen with an embedded small-diameter or standard-diameter optical fiber sensor. It was verified that the coupon specimen with an embedded small-diameter optical fiber suffered no degradation of its material properties.