A database of wideband acoustic emission (AE) modeled signals was used in Part 1 to examine the application of a wavelet transform (WT) to accomplish identification of AE sources. The AE signals in the database were created by use of a validted three-dimensional finite element code. These signals represented the out-of-plane displacements from buried dipole sources in 4.7 mm thick aluminum plates of small and large lateral dimensions. The surface displacement signals at three far-field distances were filtered with a 40 kHz high-pass filter prior to applying the WT. The WTs were calculated with a freeware software program. The effects of propagation distance, AE source type, and the depth of the AE source below the plate surface were examined. Specifically, a ratio of the WT magnitude (WTcoefficient) from the fundamental anti-symmetric mode to that from the fundamental symmetric mode was studied for correlation with the AE source type. The WT magnitudes were those corresponding to a particular group velocity and signal frequency for each mode. For sources in the large plate located at the same depth, the ratios were able to diatinguish different source types and exhibited only small changes with increasing propagation distance. But, when the variable of depth of the source was introduced, the ratios did not uniquely classify the AE source type. In the case of the small coupon plate specimen, reflections from the specimen edges distort and complicate the WTs. Since the current coupon database excludes (except for one case) the parameter of changes in the distance of the source from the coupon sides, a full examination of these complications was not possible.
Citation: Journal of Acoustic Emission
Pub Type: Journals
acoustic emission, acoustic emission modeling, source identificaiton, wavelet tranformation, wideband acoustic emission