Ultrasonic layer resonance assisted adhesive bonding for metal plates

Adhesive bonding can be enhanced with appropriate pretreatment methods, one of which includes the application of mechanical vibrations to uncured adhesives on a substrate. Previous studies have shown that high-power ultrasonic vibrations at low frequencies promote wettability between the adhesive and substrate, resulting in increased bond strength after the cure. High-frequency ultrasounds may also affect adhesion due to their unique phenomenon resulting from shorter wavelengths, but that remains unexplored. In this paper, an ultrasonic treatment assisted by layer resonance is proposed for adhesive joints. Ultrasonic vibrations are applied to a curing adhesive layer based on the resonance frequencies measured by the ultrasonic pulse-echo technique. Tensile shear tests demonstrate that the resonance of a curing adhesive layer can enhance bond strength after the cure. In particular, this treatment is shown to be effective if a frequency sweep is adopted according to an increase in the resonance frequency due to the curing process. The improvement in bond strength is associated with the relation between the processing time in the proposed treatment and the pot life of the adhesive, depending on the type of adhesive used. The findings of this paper show that the proposed treatment can improve bond strength but requires appropriate processing conditions depending on the bonding situations.