Acoustic emission theory for moment tensor analysis

Abstract

Acoustic emission (AE) is extensively applied to nondestructive evaluation of materials and structures. In the conventional AE measurement, several AE parameters are detected and analyzed to elucidate characteristics of microfracturing behaviors in materials.

Although theoretical treatment of AE waveforms was proposed more than one decade ago, the quantitative analysis was neither practical nor applicable to general AE waveforms. The crack mechanisms associated with AE generation consist of crack kinetics and crack kinematics. It has already been demonstrated that deconvolution analysis is available for determining crack kinetics. As for crack kinematics, it is known that the moment tensor analysis is promising, but has only been applied to marginal cases. In this respect, a practical procedure for the moment tensor analysis is recently formulated, selecting P wave portion from the full-space Green's function of homogeneous and isotropic material. A multi-channel observation is utilized to locate AE sources, based on arrival time differences of AE waves. Furthermore, a simplified moment tensor analysis is performed by analyzing the amplitudes of the first motions.

It is clarified that the eigenvalues of general moment tensor components are available for classifying crack types and for determining crack orientations. To implement these results into an analytical procedure, a unified decomposition of the eigenvalues is proposed.

With the emphasis on the development of this practical procedure for the moment tensor analysis, the theory of AE for the source characterization is reviewed. The results of a geological application and a test of reinforced concrete are discussed. A post-analysis is attempted to screen out poor solutions by comparing with theoretical solutions on the synthetic waveforms.