Lamb mode conversion in an absorptive bi-layer with a delamination

A theoretical study of Lamb mode propagation through an absorptive composite plate consisting of two parallel layers with a finite-length delamination dividing these layers is presented. In the delamination boundary region, noncontact boundary conditions are assumed. The calculation is based on a modal decomposition method. In thin composite plates containing a few propagating Lamb modes, as a result of diffraction on a delamination, the incident Lamb mode can be efficiently converted into transmitted Lamb modes. Delaminations in absorptive composite plates result in a considerable change of transmitted acoustic energy if the plate is characterized by substantially different absorption coefficients in the layers of the plate. In particular, the delamination can considerably increase the transmission coefficient of the incident Lamb mode if the layer where the incident Lamb mode is mainly concentrated is much less absorptive than the other one.