An algoithmic approach to improve the accuracy of AE source location was demonstrated by using a large database of wideband-acoustic-emission-(AE)-modeled signals and wavelet transform (WT) results. The AE-signal database was created by a three-dimentional, finite-element code. These signals represented the out-of-plane displacements from buried dipole AE sources in aluminum plates of 4.7 mm thickness and large lateral dimensions. The AE signals inclueded eight different source types, six or seven source depths (below the plate surface), and seven different radiation angles (from 0o to 90o). The surface displacement signals were measured at three propagation distances (i.e., 60, 270, and 522 kHz) and these regions were typically representive of the first fundamental antisymmetric mode (Ao) or the first fundamental symmetric mode (So). Additionally, a plot of the signal-propagation distances as a function of the WT-peak-based arrival times created slope-based velocities that corresponded quite closely t the relevant theoretical group velocities for the Ao or So modes. It was determined that the key frequency having the greatest WT peak magnitude always corresponded to a known mode having a known gorup velocity. The remaining two key frequenceis had their associated modes determined by means of a newly devised algorithm (which could be computer-automated) that considers the arrival times of the WT peak magnitudes but which does not require knowledge of the propagation distance nor AE-source-operation time. The algorithm also computed a range (i.e., linear distance) from a measured signal to the AE source.
Citation: Journal of Acoustic Emission
Pub Type: Journals
acoustic emission, acoustic emission modeling, finite element modeling, source location, wavelet transform, wideband acoustic emission