GENERALIZED THEORY AND SOURCE REPRESENTATIONS OF ACOUSTIC EMISSION.

Source characteristics of acoustic emission (AE) are investigated on the basis of the generalized theory previously proposed. The modeling of a crack in the generalized theory is correlated to the moment tensor representation, indicating that the principal vectors of a moment tensor represent the crack orientation and the principal values represent the principal axes of the radiation pattern emanating from the crack. Since source representations in the generalized theory are directly based on the discontinuity of displacement components, an explicit displacement distribution due to a crack can be incorporated. We studied penny-shaped cracks and rectangular moving cracks as AE sources. AE waveforms due to tensile cracks and shear cracks are also synthesized using Fortran programs for Green's functions of the second kind in a half space. Formulae to synthesize AE waveforms due to both the point and the moving dislocations and their results are presented. Effects of inclined angles of the crack orientation on the calculated wavefonns and on the inverse problem are studied. It is shown that crack orientation has considerable effects on the results of the deconvolution analysis. The moving source is found to broaden peaks of AE waveforms. These results confirm the utility and applicability of the generalized theory in elucidating fundamental mechanisms of AE.