Boundary element modeling for guided wave reflection and transmission factor analyses in defect classification

The guided wave scattering process by different defects in plate structures is studied with a boundary element method. The purpose is to separate sharp crack-like defects from smooth volumetric-like ones by analyzing the transmission and reflection factors. The traditional normal mode expansion technique has been combined with the boundary element discretization to form a hybrid BEM scheme. With this method, the scattered near-fields and the transmission and reflection coefficients of the far fields on individual modes can be obtained simultaneously. Several features related to the Lamb mode reflection and transmission process in a plate with these defect types are extracted and compared. The theoretical analysis provides a guideline for data acquisition and feature selection for use in the decision algorithm development program via neural nets.