Integrated and Flexible Ultrasonic Transducers for Structural Health Monitoring on Aircraft Structures

Fatigue crack initiating from fastener holes in aluminum plates is a typical damage frequently found on modern aircraft structures. Requirements for life extension of aging aircraft fleets and reduced maintenance costs have been accelerating the developments of structural health monitoring (SHM) technologies. This thesis considers the active sensing approach of SHM that involves the integrated ultrasonic transducer (IUT) and the flexible ultrasonic transducer (FUT). The main component of IUT and FUT was piezoelectric lead-zirconate-titanate composite films which were fabricated using the sol-gel spray technique. The crack growth monitoring capability of the IUT and FUT was successfully demonstrated on aluminum plates with fatigue cracks. The artificial damages on an aluminum test article representing aircraft structural complexity were also detected by the FUT array bonded on both planar and curved surfaces. Finally, the design and fabrication of miniature angle beam wedges having low spurious noise are presented. The fatigue crack on an aluminum thin plate was detected using the FUT bonded onto such angle beam wedges.