Acoustic reflection and radiation by thick fluid‐loaded composite plates

Abstract

The structural response function is found theoretically for a thick composite plate of infinite extent, which is composed of a thick coating layer bonded at an interface to a thick substrate layer, and which is loaded on one side by a fluid. The Timoshenko–Mindlin thick‐plate equations are used in each of the two layers to describe the flexural waves that are generated, owing either to a plane acoustic wave in the fluid impinging upon the plate, or else to a point‐force excitation of the plate. Two ideal types of interfacial bonding are considered: the ’’welded’’ bond, for which continguous plate elements on either side of the interface move in complete unison, and the ’’perfectly slipping’’ bond, for which such plate elements move in unison in the direction normal to the interface, but move completely independently in the direction parallel to the interface. From the analytic form of the structural response function of a composite plate, one can draw the following conclusions. First, there is, in general, no homogeneous plate that is equivalent to a thick bilaminar composite plate of the type considered. That is, a thick composite plate cannot be modeled by means of a simple thick plate with some sort of artificial or ’’average’’ material constants. Second, the analysis shows that the nature of the bond between the substrate layer and coating layer plays a significant role in determining the acoustic reflection and radiation characteristics of the composite plate.