Development of the Damage Detection Method for CFRP Structures Using Distributed BOCDA Optical Fiber Sensor

Abstract

The Brillouin optical correlation domain analysis (BOCDA) technology is one of the distributed optical sensing technologies utilizing the Brillouin scattering phenomena. The authors are developing, verifying and validating this technology. They are also developing the installation technique of optical fiber sensors, evaluating the durability of the BOCDA system and manufacturing the new device compatible to avionics bays for size. Furthermore, the authors are also improving the monitoring ability for composite damages. This paper reports the developmental status of the BOCDA monitoring ability for composite damages such as debonding at adhesive joints and micro-damages at bolted joints. First, debonding detection tests were conducted using carbon fiber reinforced plastics (CFRP) stiffened or repaired panels. In this test, test plates with a sheet stringer or a repair patch were applied tension load, and expanding of debonding areas was monitored by measuring strain distribution changes near these areas. Second, bearing damage detection tests were conducted using CFRP bolted joint specimens. In this test, multi-fastener single-lap CFRP specimens were applied tension load, and occurrences of micro-damages near bolt holes was detected. Micro-damages were detected by monitoring shapes changes of the Brillouin Gain Spectrum, which is one of the BOCDA measurement results.