Laser Ultrasonic Imaging of Built Facilities for Improved Lifecycle Management

Abstract

Australia’s ageing infrastructure is in great need of a reliable monitoring technique. However, large dimensions, heterogeneous materials and complex shapes are challenges that must be circumvented. Ultrasonic waves are able to map incipient structural damages but they attenuate and maintaining reliability of the signals over the relatively large structural distances is a challenge. Thus, a high power ultrasonic technology would be useful for structural health monitoring. Recent developments in laser ultrasonic techniques have opened up the opportunity for remote inspection of large structures on account of its non-contact nature and its ability deliver a higher magnitude of energy (~1 Joule) in comparison to the existing methods (order of μJoule). Moreover, contact ultrasonic techniques, such as PZT based systems, rely greatly on the contact pressure between the PZT transducer and the surface under inspection. Laser ultrasonics can be totally non-contact and thus it alleviates the uncertainty of contact. Further their application can be extended to corrosive, hostile, geometrically larger and difficult to reach locations. In this paper, a laser based non- contact ultrasonic system is presented. Ultrasonic guided waves in the specimen are generated by means of Nd-YAG Pulsed Laser and the waveforms from these techniques are detected using non-contact Laser Doppler Vibrometer (LDV). The efficacy of laser systems has been illustrated with both amplitude and frequency response plots for a corroding steel bar.