Scattering of the Fundamental Symmetrical Lamb Wave Mode by a Small Edge Crack in an Isotropic Plate

Abstract

Lamb waves have a relatively slow geometrical decay of amplitude with propagation distance, which makes them well suited for wide-area inspection and SHM (structural health monitoring). This paper presents an extensive computational study of the interaction of the fundamental symmetrical Lamb wave mode (S0) with a through-thickness edge crack in an isotropic plate. The incident wave is generated by a point source that is symmetrical with respect to the plate's midplane, and whose time dependence is a 10-cycle Hanned windowed toneburst of centre frequency below the cut-off for the first order shear-horizontal mode (SH1), so that the only propagating modes are S0 and SH0. Results are presented showing the angular dependence of the S0 and SH0 scattered fields for various angles of incidence. The dependence of scattering amplitude on crack size is also studied, with a view to facilitating the inverse problem of determining crack size from measurements of the scattered field. It is shown that the scattered field due to a small crack can be considered to be equivalent to a point source consisting of a combination of force doublets that depend on the angle of incidence. The implications of these results for SHM are briefly discussed.