A thin adhesive film, located between two bonded adherents, is capable of localizing the energy of elastic waves in the form of an interface wave. Under study are the phase velocity and transmission losses of the interface wave which were measured during the entire course of polymerization of the adhesive. It is shown that the phase velocity of the interface wave and the effective shear modulus of the interface film, calculated from the velocity data, are related to the strength of the adhesive bonds. The general transmission loss factor, which is a function of the relaxation maximum of losses arising during the course of polymerization of the adhesive, is another parameter correlated with the strength. The shear strength of the joint was determined on a special specimen in the form of a lap joint, which was also used for acoustic measurements.

The waveguide properties of a thin film separating two elastic half-spaces possessing a shear modulus higher than the shear modulus of the film are investigated. It is shown analytically and experimentally that such a film is capable of localizing the energy of elastic waves near the interface. The velocity of the interface wave is determined by shear modulus, density, thickness of the film, and by the elastic properties of the substrates. The velocity of the interface wave lies between that of the Rayleigh and that of the shear waves in the solid half-spaces. It is shown that the interface wave can be used to estimate the elastic and dissipation properties of thin interface layers.