Barely visible impact damage detection and location on a real scale curved CFRP fuselage panel with optical fibre Bragg grating sensors

Current CFRP aircraft structures can suffer from barely visible impact damage (BVID). These BVIDs can grow due to the operational loads applied on the damaged structure and can eventually even compromise their load-bearing functionality. To detect these BVIDs as soon as possible, aircraft are frequently submitted to on-ground inspections, which increase downtimes and associated costs. A permanently installed sensor network could overcome these shortcomings. Optical fibre sensors have been proposed as possible candidates for such networks owing to their light weight, their small diameter, and their immunity to electromagnetic interference. In this work we use a network of four flight-compatible optical fibres, with a total of 120 fibre Bragg grating (FBG) sensors, to monitor the damage-prone stiffener feet on a large curved CFRP panel of 5 × 3 m2. We created BVIDs of calibrated size at the damage-prone locations and we use the response of all 120 sensors to detect and locate the BVIDs. To do so, we first consider temperature effects between the baseline and inspection measurement, and second, we quantify the health of the component based on all sensor readings and test it against a damage threshold.