Influence of the oxide layer on the quality of bonding in adhesively bonded metallic structures by ultrasonic guided waves

Abstract In adhesively bonded metallic structures, the oxide layer is a primary component of the micro-composite layer at the adhesive/adherend interface whose morphology plays a critical role in the strength and durability of the joint. The role of the oxide layer in detecting the level of adhesion in bonded aluminum joints is examined in the present work through the dispersion spectrum of ultrasonic true guided waves. The dispersion curves are calculated for an aluminum/epoxy/aluminum sample, where the adhesion between the epoxy and aluminum is modelled by a spring-mass model at both the interfaces. The variation in the ratio of the thickness of oxide to the primer layer is incorporated into the mass term of the model and its effect on the dispersion curves is studied. It is observed that adhesive-adherend interlayer thickness influences the higher-order symmetric modes at higher phase velocities and this influence is heavily dependent on the effective material properties of this interlayer.