Health monitoring of complex curved structures using an ultrasonic wavefield propagation imaging system

Abstract

An ultrasonic wavefield propagation imaging system is introduced and then applied for ultrasonic wavefield imaging of complex curved surfaces. A Q-switched pulsed laser is utilized as a moving ultrasonic generator, and a PZT ultrasonic sensor is fixed during the laser beam scanning and detects the ultrasonic waves propagated from the points excited by the laser beam. The waveforms are allocated in the spatial domain of the scanned points and then manipulated in the form of a time versus wavefield movie. The visualized wavefields enable easy detection and interpretation of structural defects because anomalies during wavefield propagation can be visualized. Furthermore, this ultrasonic wavefield propagation imaging system enables reference-free inspection, complex curved surface scanning because it does not require control of focal length and incidence angle of the laser beam, and excellent adaptability with built-in structural health monitoring sensors, such as piezoelectric and fiber optic sensors. The system is demonstrated in the applications of wavefield visualization on a drill surface, detection of mass loss parts inside an elbow pipe joint, and detection and characterization of impact damage and stringer disbond in a composite skin–stringer structure.