We equipped a composite wing structure fiber Bragg grating (FBG) arrays including 246 FBGs with 10 mm gauge
length, eight and six long-length FBGs with 300 mm and 500 mm, respectively. The length of the wing was 6 m and it
was made of carbon fiber reinforced plastics (CFRP). The sensing system based on optical frequency domain
reflectometry (OFDR) was used in a series of load tests. The measured results by FBG arrays showed the overall
deformation of the wing and good agreement with analysis results. Additionally, strain distributions of stress
concentration zones were successfully measured by long-length FBGs.
High spatial resolution and sensitivity are required in distributed strain measurements for structural health
monitoring. We have developed a distributed strain sensing technique with long gauge FBG sensors, which
enables to measure strain at an arbitrary position along the FBG sensors with the high spatial resolution less
than 1 mm based on optical frequency domain reflectometry (OFDR). In this paper this technique with a 1500
mm gauge length FBG was applied to monitoring strain distributions of a simply supported beam subjected to
bending loads. The agreement between the measured strain and the theoretical one is excellent. Also we
succeeded to identify the applied load by the inverse analysis from the measured strain distribution data, and
confirmed the validity of these methods.