High Frequency Elastic Wave Propagation in Large Structures using Spectral Elements and Perfectly Matched Layer

The influence of mechanical noise in an Acoustic Emission (AE) testing still obscures its successful application in monitoring various structures and systems. While advances in pattern recognition algorithms are helpful to differentiate relevant data from captured noise, the algorithms fail if the characteristics of relevant data are unknown. A better scientific understanding of the characteristics of elastic waves due to damage mechanisms in a structure is needed for developing a quantitative measurement approach of damage (e. g. frequency content, type, orientation) based on the AE method. The results of small scale coupon tests cannot be directly used in large scale structures due to the influence of boundaries on propagating waves detected by the AE sensors. In this paper, a steel plate is modeled using an absorbing boundary condition and spectral elements in order to understand the direct wave release from damage without influenced by reflections. The selected absorbing layer is perfectly matched layer (PML), which is designed such a way that wave reflections from boundaries back into the solution domain regardless of frequency or angle of incidence are prevented through providing a stable solution and satisfying the Sommerfeld radiation condition. The displacement-based and timedomain equations of PML are utilized. The numerical results of the two-dimensional metal plate with absorbing boundary condition are validated with extended-geometry numerical models and experimental results.