Monitoring of fatigue crack growth in composite adhesively bonded joints using Fiber Bragg Gratings

AbstractOptical sensors, like Fiber Bragg Gratings (FBG), can be easily embedded into composite structures, thus obtaining structures with health monitoring capabilities. In this work, fatigue crack growth in adhesively bonded joints of thick composite laminates was experimentally investigated using FBG. An array of equally spaced sensors was applied to the side of a single lap tapered joint, in order to simulate its embedment into the composite laminate. The position was chosen on the basis of finite element analysis of the strain distribution and the expected response of the sensors was also simulated by means of a T-matrix model. The position of the crack tip was monitored using both an optical microscope and an ultrasonic phased array sensor. A good correlation between the crack tip position and the variation of the signal provided by FBG indicate that the proposed configuration of FBG array can detect and monitor a fatigue crack in the adhesive joint, even in case of de-lamination of the first composite's plies