Crack Identification by Source Inversion Analysis of AE Wave Motions

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The aim of the present research is to develop a technique which can identify crack kinematics from acoustic emission (AE) wave motions. Theoretically, AE waveforms are represented by an integral formulation based on the boundary element method (BEM). Introducing a dislocation model as a mathematical model for a crack, the moment tensor representation is derived.The moment tensor consists of elastic constants, a direction vector of the unit normal to crack surface, and a direction vector of crack motion. Thus, crack kinematics on crack type and crack orientation are recovered, provided that six independent tensor components are fully determined. For this purpose, a computer software named SiGMA (Simplified Green's function for Moment tensor Analysis) is developed. Following the eigenvalue analysis of moment tensor components and a unified decomposition, AE sources are classified into tensile cracks and shear cracks. Crack opening direction of the tensile crack is obtained from the direction of the first eigenvector. The direction of shear motion is recovered from the directions of the first and the third eigenvectors.The inversion procedure developed is applied to AE data on in situ hydrofracturing tests and fracture tests in concrete. Numerical studies on hydrofracturing tests confirm the reasonable accuracy of the proposed procedure. Results of cylinder-tensile tests and pullout tests of anchor bolt show a great promise for identifying crack kinematics by AE inversion procedure.