Modeling of acoustic-emission wave propagation in layered media

Abstract

This study proposes a model for acoustic-emission (AE) wave propagation in a layered medium, which can be used for damage detection in structural health monitoring in general, and crack identification in non-destructive testing and evaluation for materials in particular. In the model, the materials are characterized by piecewise, layered media with one surface as free and the other as free, fixed or infinite. The AE waves are generated by dislocation over a fault area located in one of the layers or at a layer-to-layer interface. In this study, three-dimensional (3D) wave motion in each homogeneous, isotropic and linearly-elastic layer is solved with the use of an integral transformation approach. The 3D wave motions are decomposed into 2D wave motion with coupled P-SV waves and 1D with SH waves in a transformed, frequency-wavenumber domain, where P and S indicate respectively compression and shear waves, SH denotes a shear wave component with particle motion direction parallel to the free surface, and SV perpendicular to SH motion direction. Wave reflection and transmission at layer-to-layer interfaces, boundaries and in a layered medium are derived in terms of wave scattering matrices in a transformed domain. A closed-form solution for wave responses to a point, unit-impulse dislocation is derived in the transformed domain, which can then be used to construct the wave responses to a finite time-dependent dislocation source and converted in a time-space domain. With the model, this study examines AE wave propagation features in general, and wave responses at a free surface in particular from the perspective of damage detection. Numerical examples are provided for illustration.