Abstract: The slow modulation of the interfacial capillary-gravity waves of two superposed fluids with uniform depths and solid walls is investigated by using the method of multiple sca.les.The evolution of a packet is described by the nonlinear Schrodinger equation, and then the stability of the so-called Stokes wave train is discussed.

Key words: interface layer, antiplane shear, failure, shear beam model, instability, snap-through, snap-back, damage