Real-Time Stress Concentration Monitoring of Aircraft Structure During Flights Using Optical Fiber Distributed Sensor with High Spatial Resolution

For efficient and reliable design and operation of aircraft, monitoring of deformation and strain during flights is beneficial. Stress concentration is specifically critical for structural integrity, whereas it is a difficult phenomenon to predict and accurately observe. Optical fiber sensors are highly applicable for this purpose because they are light-weighted and flexible, which allows less invasive installation to aircraft structures. In addition, they are capable of distributed monitoring, which enables efficient measurements by collecting strain distributions along a single fiber. We have developed an optical fiber distributed sensing technique with a high spatial resolution which allowed us to monitor strain distribution profiles and stress concentrations. We use long-length fiber Bragg gratings (FBGs) and optical frequency domain reflectometry (OFDR). The OFDR-FBG technique allows us to monitor real-time strain distributions during flights along the FBGs with a 1.6 mm spatial resolution and a 151 Hz sampling rate. We applied this monitoring technique to a middle-sized flying test bed, and conducted flight tests. We measured strain distributions of a fuselage stringer, an aft-bulkhead and a main wing during flights. We report time histories of strain distribution profiles during various maneuvers especially focusing on stress concentration areas. We also show a record of accumulated strain experiences of the wing, which is expected to be an essential feedback for fatigue analysis.