Cutting-off effect at reflection-transmission of acoustic waves in anisotropic media with sliding-contact interfaces

The specific feature of the interface, which maintains sliding contact betw een elastic media, is that it can be impervious to the wave field existing in one of the adjoined materials. As a result, reflection-transmission of p lane acoustic waves at the sliding-contact interface may enjoy the cutting- off effect, which implies that neither bulk, nor inhomogeneous modes are be ing transmitted at particular angles of incidence. The necessary and suffic ient criteria for this phenomenon are obtained for a binary structure, cons tituted by two elastic half-spaces in sliding contact, and for a sandwich s tructure with sliding-contact interfaces between the enclosed layer and the substrates. In the generic case of unrestricted anisotropy (triclinic mate rials), the criterion for cutting-off in a binary structure involves acoust ic parameters of solely that of the half-spaces, which contains the inciden t mode, and proves to be independent of an adjacent medium. The frequency-d ispersive criterion for the absence of transmission through a triclinic lay er in the sliding-contact sandwich structure is independent of substrates. By appeal to the Stroh formalism, the cutting-off conditions in a binary an d a sandwich structure are further elaborated under the assumption that one of the half-spaces, or a layer, is orthorhombic, and its two symmetry plan es are parallel, respectively, to the plane of incidence and to the sliding -contact interface with arbitrary adjacent media. It is shown that the tran smission cut-off in a binary structure is necessarily accompanied by the ab sence of mode conversion at reflection, but the reverse is not true. The an gles of incidence which give rise to these effects are determined in terms of elastic coefficients. Transmission cut-off through an orthorhombic layer comes about at an arbitrary angle of incidence, related to guided-modes ra nge in the layer, for the corresponding aperiodic infinite set of the frequ ency values. Relations for the coefficients of reflection and transmission at the sliding-contact interface between two orthorhombic half-spaces are o btained in concise form, expressed solely via normal components of the part ial Stroh-normalized traction amplitudes. Provided that the adjoined orthor hombic half-spaces in sliding contact are identical, the same value of wave -vector tangential projection, which stipulates transmission cut-off at the incidence of, say, the fast mode, entails total transmission at the incide nce of the slow mode. (C) 1999 Elsevier Science B.V. All rights reserved.