We propose a novel technique that utilizes point source excitation and detection of Lamb waves through dry, elastic contacts to monitor thickness changes of plate-like structures. A pair of pin transducers are used to excite and detect the A₀ mode Lamb wave in a test plate or a pipe wall and the wave velocity is obtained by time of flight measurement. Any change in plate thickness can be detected by the change in the Lamb wave velocity due to the dispersive nature of the A₀ mode. We demonstrate the power of this approach in ultrasonic pipe erosion/corrosion monitoring and its potential application in aircraft skin defect imaging. We present results of thickness measurements of a test plate with 1 percent accuracy, and erosion/corrosion monitoring in a section of pipe that was removed from service, as well as imaging of defects in an aluminum thin plate.

Date Published: 14 November 1996
PDF: 8 pages
Proc. SPIE 2945, Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware, (14 November 1996); doi: 10.1117/12.259118

Published in SPIE Proceedings Vol. 2945:
Nondestructive Evaluation of Aging Aircraft, Airports, and Aerospace Hardware
Raymond D. Rempt; Alfred L. Broz, Editor(s)