On symmetry-breaking effects in propagation of waves in sandwich plates with and without heavy fluid loading

This paper addresses analysis of wave motions in an unbounded sandwich plate with and without heavy fluid loading in the plane problem formulation. The effects of coupling of otherwise independent upon each other in-phase and anti-phase (with respect to the transverse motion of skins) modes, which could be produced by uneven pre-stress of the skins, uneven properties of the acoustic media on the opposite sides of the plate, or by a difference in properties of the skin plies, are brought to light. These effects are called hereafter ‘symmetry-breaking’ for brevity. Although the suggested methodology is applicable to treat the above-mentioned cases in a general manner, this paper is concerned with the use of classic perturbation theory to study coupled in-phase and anti-phase modes in a plate of symmetric composition. The coupling perturbation parameter is introduced and is shown to be asymptotically small. The predictions of the perturbation theory are compared with the direct solutions in the cases of regular and singular perturbation and very good agreement is observed.