Damage detection of CFRP using fiber Bragg gratings

In maintenance of composite structures, a structural health monitoring method called active sensing diagnostics has recently been paid much attention. An active sensing system contains actuators and sensors so it generates plate waves in the structure and monitors the response. The integrity of structures can be monitored from the response to plate waves because damage in structures affects the propagation properties of plate waves. In previous studies on active sensing diagnostics, piezoelectric (PZT) devices were used as sensor. There is a great advantage in practical application if fiber Bragg gratings (FBG) can be used as sensor in active sensing. This is because a FBG is lightweight, small size and immune to electromagnetic interference, moreover, can be multiplexed. The objective of the present study is to verify the possibility of active sensing diagnostics using FBG sensors. A cross-ply CFRP having visible damage was used as the material to be monitored. Plate waves were propagated through an intact area or a damage area and were detected with FBG sensors. The influence of the existence of damage on FBG sensor response was investigated.