Acquisition and analysis of ultrasonic wavefield data to characterize angle-beam propagation and scattering in plates

Abstract

A method for acquiring and analyzing ultrasonic wavefields to characterize scattering from defects is described. A laser vibrometer and XY scanner are used to record high resolution wavefield data for angle-beam waves propagating in both a defect-free plate and a plate containing crack-like defects emanating from a through-hole. The properties of angle-beam wave propagation are first studied, which include wave generation mechanisms, propagation trajectories, and apparent phase velocities on the measurement surface. Scattering from a defect of interest is then analyzed by subtracting wavefields recorded before and after introduction of the defect. Wavefield subtraction is very sensitive to unavoidable spatial misalignment, which must be corrected prior to subtraction. Two methods for aligning wavefield data sets prior to subtraction are described and their performance is assessed. Several methods for characterizing scattering, including radial energy plots and scattering patterns, are described and used to quantify scattering from the introduced defects. Finally, efficacy of the scattering characterization methods is discussed and recommendations are made for future work.