Spectral Analysis of Acousto-Ultrasonic Waves for Defect Sizing

Abstract

A study of the feasibility of employing acousto-ultrasonic (AU) testing to size defects has been carried out using a model system consisting of a single defect in a glass matrix. A through-transmission mode was used for the AU testing and the output signals were analysed by a counting technique (cumulative ringdown count, CRDC) and spectral analysis. The CRDC decreased with increasing defect size but the scatter in the data did not allow accurate sizing. The frequency spectra exhibited multiple peaks which occurred at constant frequency intervals. The frequency interval decreased with increasing defect size and this could be attributed to either multiple time delay or a resonance effect or to both phenomena. Most evidence supported the resonance effect and good agreement was found between defect size calculated from AU data using a resonance theory and that measured optically