In Part 2, (Part 1 Source Identification) the same finite-element-generated database of acoustic emission (AE) signals was used to examine the application of a wavelet transform (WT) to improve the accuracy of AE source location. The method utilizes a WT result to select AE signal arrival times for a single group velocity from energetic modes. Both the large plate case without edge reflections and the small plate (coupon) with multiple edge reflections were examined. The arrival time of a specific frequency of an energetic fundamental mode of the far-field signals was determined from the WT. Using these arrival times at three propagation distances, a group velocity was determined for comparison with the appropriate group velocity based on dispersion curves. Both filetred narrowband (100 to 300 kHz) and wideband (40 kHz high-pass signals were examined. In addition, in the large plate case, experimental sensor/preamplifier electronic noise was added to the AE signals to examine the effect of noise on the determination of accurate arrival times as a function of signal-noise (S/N) ratios. The large plate results indicate that very accurate arrival times can be determined that correspond to a particular group velocity. In the coupon case, the results indicate significant distortions in the arrival times due to the multiple edge reflections. The perturbation due to the presence of electronic noise was relatively small for the case of the wideband signals in the large plate until signal-to-noise ratios reached levels where an AE hit would likely not be recorded.
Citation: Journal of Acoustic Emission
Pub Type: Journals
acoustic emission, acoustic emission modeling, source location, wavelet transform, wideband