Non Destructive Tests of Structural Bonds by Guided Ultrasonic Waves: Effect of a Surface Pretreatment or a Localized Defect

The aim of this study was to propose a non destructive method to test the mechanical quality of a bond aluminium/epoxy/aluminium. Thus, for each aluminium/epoxy interface, an intermediate interface modelling between a simple geometrical interface and an interphase (3D material medium), i.e. a 2D material medium. In order to describe the surface stresses, we introduce the surface free energy (the surface tension). This parameter appears in the jump conditions of stresses and displacements at each aluminium/epoxy interface. So, it influences the ultrasonic waves propagation and particularly the guided modes of the tri-layer structure. The results show that the surface free energy does not arise at normal angle of propagation, whereas near the Rayleigh angle, the behaviour of the A₀ and S₀ Lamb modes varies strongly according to its value. Such a modelling seems well adapted to take into account the pre-treatments of the aluminium plates or some localized interface defects.