The classification of acoustic emission source mechanisms based on features related to the physics of acoustic emission
signal generation is considered in this paper. Numerically generated acoustic emission waveforms are used for this
purpose. Conventional acoustic emission parameters such as rise-time, duration, and frequency content do not
effectively characterize acoustic emission waveforms for the purpose of identifying the source mechanisms. Features
unique to the different source mechanisms and relative positions of the sensor with respect to the source were identified
and extracted from numerically obtained acoustic emission waveforms. This feature selection appears to be successful in
capturing the differences related to the source mechanisms considered here. Correlation coefficients of the 45 features
with different waveforms were first obtained, and their principal components determined. The dominant principle
components were found to adequately characterize the waveforms and relate them to their source mechanisms. Better
than 90 percent success was seen when only the first two principle components were employed, even in noisy signals
considered here.
Identification of the source mechanism and measurement of source strength are important requirements for wider field
application of the acoustic emission technique. It is difficult to relate a given source event to resulting acoustic emission
waveforms in experimental results. However, it is practical to simulate such source events using numerical simulations
and examine the resulting waveforms. The present paper uses such an approach to identify the patterns embedded in the
waveforms and their variation with relative positions of the source and sensor. Important elements in the waveforms are
shown to have strong variation with respect to the relative positions of the source and sensor. The resulting amplitude
variations should be taken into account in the measurement of acoustic emission source strength. In addition, it is shown
that the shear horizontal wave has a prominent component in the normal stresses in the radial direction. Acoustic
emission waveforms obtained from the numerical simulations were also used to demonstrate pattern classification of
these waveforms and identify the source mechanisms. The three elements of the waveforms, So, Ao, and Shear, were
considered as the basic elements of the waveform. These elements have different frequency bandwidths that are directly related to the impulse duration of the incremental crack growth. Correlation coefficients between these elements and the acoustic emission waveforms were used as a means for identifying the source type.
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