The Use of Ultrasonic Guided Waves in Cure Monitoring of Adhesives

Adhesive materials, according to their different characteristics, are widely applied in the industry; therefore, it is vital to monitor the curing process. This paper experimentally illustrates the applicability of ultrasonic Lamb waves to determine the curing phase of Polymax (PX) and Primer (Pr) adhesive layers, which are bonded over a finite size of an aluminum plate. Lamb waves generate and detect using piezoelectric transducers that are coupled on the aluminum plate. Because of the sensitivity of Lamb wave signals to the physical changes of adhesives during the cure cycle, the amplitude difference (AD) of two neighboring signals is employed to determine the phase of each curing stage: liquid state (uncured), semi-liquid state (semi-cured), and solid-state (fully-cured). The analysis of the adhesive phases exhibits good agreement with the recommended cure time by the manufacturer and shows the distinctive nature of PX and Pr adhesives, making the ultrasonic Lamb waves an appropriate technique to assess the adhesives status. This study can also be applied to the cure monitoring of PX and Pr adhesives as reference data.