Based on the results of an earlier study, a specific scheme was demonstrated to identify acoustic emission (AE) source types using ratios of Lamb-wave modal amplitudes from two radiation directions in a 4.7 mm thick aluminum plate. The modal amplitudes were obtained from certain peak magnitudes of wavelet transforms (WT) of the AE signals at a propagation distance of 180 mm. The peak magnitudes were taken from energetic frequency-mode combinations. These combinations were the fundamental modes AO at 60 kHz, So at 270 kHz and So at 522 kHz. The AE signal database was obtained using a validated finite element model (FEM) for three different source types, each located at six or seven depths in the plate that had large lateral dimensions. The technique of source identification was demonstrated using ratios of the WT -determined modal magnitudes of the signals at a radiation angle of 45 degrees divided by those from a zero degree angle. Then, the effect on source identification of adding electronic noise (sensor/preamplifier) to the FEM signals was studied. Due to the random nature of the experimental wideband noise, a statistical study was necessary .At each signal-to-noise (S/N) ratio, 50 cases were examined for certain depths of each source type. The percentage of correct source identifications was determined as a function of the S/N ratio. To obtain a high percentage of correct identifications, a S/N ratio of at least six to one was found to be necessary.
Citation: J. Acoust. Emiss.
Pub Type: Journals
acoustic emission, acoustic emission modeling, AE, electronic noise, finite-element modeling, modal AE, source identification, wavelet transform, wideband acoustic emission