Propagation of transient ultrasound in thick annular waveguides: modeling, experiments, and application

Abstract

A wave mode expansion solution is formulated for transient excitation of circumferential waves in a thick annulus. The excitation is a distributed traction source on the outer surface modeling a piezoelectric transducer with an angular wedge. The solution provides valuable information on the modal content of the detected signals and the radial dependence of the ultrasonic field within the waveguide. The predicted waveforms are compared with experimental results obtained with several transducers, for various transducer wedge angles, and for various positions of the receiver on the outer surface. The trends predicted by the model are confirmed by the experiment and lead to the selection of good operating parameters (frequency, wedge angle and type, and source–receiver position) for the detection of cracks present on the inner surface of the waveguide. The time-windowed, band-limited wavelet transform of the signal is found to be an effective means to localize the cracks. The technique is successfully tested on a partially annular component of the pitch shaft of the H-46 helicopter.