Characterization and mechanism of accelerated curing of adhesives by in situ ultrasonic vibration for bonded joints

Ultrasonic vibration can accelerate the curing of epoxy compounds. Previous studies have not explored the nonthermal effects of ultrasound. In this article, we show the accelerated curing process using in situ ultrasonic vibration that removes the thermal effect. The acceleration mechanism of nonthermal effects is clarified. Bisphenol A epoxy resin/low molecular weight polyamide 650 system was used as the adhesive of the joint, and carbon-fiber-reinforced plastic (CFRP)/aluminum alloy joint was used as the bonding object. Ultrasonic vibration was applied in situ to the CFRP laminate in the joint through an ultrasonic tool head. Fourier transform infrared spectroscopy and differential scanning calorimetry were used to characterize the process of conventional curing and ultrasonic curing of adhesives. Results show that the curing rate of the adhesive can be increased by 2500%. By improving the Kamal model, we describe a new model that can describe the ultrasonic curing process very well. The model shows that ultrasound can reduce the activation energy. Temperature monitoring confirmed that pulsed ultrasound can maintain the temperature of the adhesive stable during the curing process. Dynamic thermomechanical analysis showed that pulsed ultrasound accelerates the curing process and improves the mechanical properties of the adhesive. Ultrasound promotes mass transfer between the resin and the curing agent and increases the collision probability between the reactants, thus increasing the reaction rate.