Structural Health Monitoring and Non Destructive Testing of fatigue crack growth in bonded CFRP-CFRP Lap Joints

Nowadays, adhesive bonded joints are extensively employed in lightweight structures, particularly in naval, automotive and aerospace industries. Anyway, troubles could arise from manufacturing defects and operational loads, likely causing local disbonding. In the present paper, fatigue-tests are performed onto bonded CFRP-CFRP single lap joints: damage initiation and propagation is investigated using a well-established advanced Phased Array ultrasonic inspection and two different SHM techniques. In particular, the first SHM technique is based onto surface mounted Fiber Optics, whereas the second onto piezoelectric sensors, arranged in a Pitch-Catch configuration, for the emission and sensing of Guided Waves. A good correlation is found between crack tip location, strain peak profile recorded by distributed fiber sensing technology and PAUT inspections, while Guided Waves allows the definition of an energy based Damage Index as an effective way for monitoring lap-joint degradation during fatigue loads.