Scaled behavior of interface waves at an imperfect solid-solid interface

Abstract

Laser ultrasonic techniques allow the remote analysis of adhesion mechanisms at imperfect interfaces up to GHz frequencies. However, the sensitivity of interface waves to the properties of the contact is not very well known. In the present work, the mechanical boundary conditions are described considering that the contacting solid half-spaces are connected by tangential and normal springs. Such a modeling implies a discontinuity of the displacement field across the interface. To identify the relative amplitudes of the different types of interface waves—skimming, leaky Rayleigh (LR) and Stoneley (St) waves—a semi-analytical time domain model describing the thermoelastic laser generation is derived. The results illustrate the influence of the boundary conditions on the attenuation of the LR wave and on the existence of the St wave. In addition, a single compact and elegant dispersion equation is presented to investigate the behaviour of the interface waves propagating along a generalized imperfect boundary. Such analysis reveals the existence of a cutoff frequency fc close to which the St wave behaves like a skimming transverse wave. A scaled analysis demonstrates that two master curves suffice to describe the dispersion of LR and St waves and that fc is inversely proportional to the tangential interfacial spring constant.