Nonlinear modulation of Lamb modes by clapping delamination.

The nonlinear interaction between a high frequency probing Lamb wave and a bilayer containing a tangential delamination at the interlayer interface, whose contact conditions are dynamically changing due to a high amplitude Lamb wave with a long wavelength, is modeled in a quasistationary approach. The impact of the evolution of the contact condition on the mode conversion coefficients that describe the interaction of the probing wave with the delamination region leads to spectral enrichment due to cross-modulation spectral components between the probing wave and the modulating wave. The dynamical behavior of the normal displacement at the externally accessible surfaces is investigated for two different types of incident probing wave, both for an absorbing and a nonabsorbing bilayer structure, for variations in the contact quality modulation and as a function of defect size. The results can serve as a parametric guide for experimentalists considering the use of nonlinear harmonic generation of Lamb waves as a tool for nondestructive testing of bilayers, such as rubber-steel composites, in storage tanks and pipelines.