DEFECT DETECTION IN MULTI‐LAYERED STRUCTURES USING GUIDED ULTRASONIC WAVES

This contribution presents a preliminary study for the in‐situ monitoring of fatigue crack growth at fastener holes in multi‐layered aircraft structures, using low frequency guided ultrasonic waves. The investigated model multi‐layered structure consists of two adhesively bonded aluminum alloy tensile specimens. Guided waves were excited using multiple piezoelectric discs. The resulting wave field in the specimen was measured using a laser interferometer and compared to numerical simulations. The influence of a defect on the scattered wave field around the fastener hole was studied. During fatigue crack growth, changes in the amplitude of the ultrasonic signal at a single point were monitored and correlated to the optically measured crack length.