Material interface inspection by Lamb waves

In this paper an investigation on the Lamb wave propagation through a two-layered glass plate with different interface conditions between the layers is carried out to study the effectiveness of Lamb waves in detecting defects at the interface as well as estimating the interface strength. To this end the stress field inside the two layered plate is theoretically calculated for different interface conditions and for a number of propagating Lamb modes. It is observed that, for every Lamb mode, the stress field inside the plate varies significantly with depth. Symmetric modes generate maximum normal stress and zero shear stress at the central plane; the situation is reversed for the antisymmetric modes. it is found that the Lamb modes which produce large shear stress at the interface position are most sensitive to the shear stiffness of the interface. Void and delamination type defects that release the interface stress affect those Lamb modes most significantly which produce high stress at the interface position. Theoretical predictions have been experimentally verified.