Detection of Sub-surface Delamination based on the Spatio-temporal Gradient Analysis over the A0-mode Lamb wave Fields

This study proposes a novel method of local phase velocimetry based on the spatio-temporal gradient analysis. Structural flaws such as sub-surface delamination, corrosion and fatigue cracks represent changes in effective thickness and local properties of materials, and therefore, measurement of phase velocity changes in elastic wave propagation can be employed to assess the integrity of material structures. Due to the dispersive character of the A0-mode Lamb wave, the phase velocity of Lamb wave is varied depends on the thickness of the plate. Hence, a measure of the local phase velocity of the A0-Lamb wave yields a measure of the sub-surface delaminations of the plate. Theoretical analysis and several numerical experiments show the principle of the proposed method in this paper.