Harmonic resonance of nonlinear SH waves on a two layered elastic medium

In this work, the harmonic resonance of SH (shear horizontal) waves in a two layered elastic plate of uniform thickness is considered. Both layers are assumed to be homogeneous, isotropic and incompressible elastic and having different mechanical properties. Stress and displacements are continuous at the interface of the layers. Also, free surfaces of the layers are free of tractions. Under these assumptions, the equations of motion and boundary conditions governing the propagation of nonlinear SH waves in this elastic media are derived. Then, the occurence of harmonic resonances and the fifth harmonic resonance are examined in detail. It is shown that the governing system for the slowly varying amplitudes of the fundamental wave and its fifth harmonic is a pair of two coupled NLS (nonlinear Schrödinger) equations.