Monitoring of cracks near fastener holes using direct-write ultrasonic transducers

Structural health monitoring (SHM) using direct-write transducers is an emerging technology wherein the piezoelectric ultrasonic transducers are directly produced on the structures using scalable in situ processing method. In contrast to implementation of discrete piezoelectric transducers by manual installation as in existing SHM technologies, the direct-write transducer technology is promising for achieving the long-envisioned smart structures with self-diagnostic function, with the advantages of improved reliability, lowered cost, minimized weight and lowered profile. In this work, direct-write piezoelectric ultrasonic transducers were designed and fabricated near fastener holes in aluminum structures for evaluating the feasibility of monitoring the structural integrity around the holes. Notches and fatigue crack were produced from the holes, and the ability of detecting the notches and crack using the direct-write transducers was investigated by comparing the ultrasonic signals and evaluating appropriate damage indexes related to ultrasonic energy. The results and analyses show the potential of applying direct-write ultrasonic transducers for SHM around fastener holes.