Monitoring the Curing of Epoxy Resin Accelerated by Ultrasonication via Impedance Measurements

Carbon Fibre Reinforced Polymers (CFRP) play a vital role in various sectors, particularly aeronautics and automotive sectors, due to their exceptional properties, including high strength, stiffness, and corrosion resistance. These advantages, however, are counterbalanced by a complex manufacturing process with unique challenges, such as non-uniform curing that degrades performance. This work addresses two key aspects of curing: (a) the continuous monitoring of epoxy resin curing through non-destructive electrical impedance measurements, and (b) the potential benefit of additional ultrasound energy on the curing process to counteract non-uniform curing.

Electric impedance measurements offer a distinct advantage over conventional thermal analysis methods, allowing for continuous real-time monitoring throughout the entire curing duration. Sensor probes mounted on the surface are used to track changes in their equivalent capacitance and resistance, caused by the curing within the material. This approach can be an effective, non-destructive way to assess the local curing status of the resin.

Recent studies have indicated that high-intensity ultrasonic fields can significantly accelerate the curing of epoxy resins. However, there remains a critical need to differentiate between the thermal effects induced by ultrasound and the mechanical effects related to the added vibrational energy, and to develop a non-destructive, and continuous monitoring procedure that effectively separates these influences. Experiments were conducted using an ultrasonic bath to demonstrate the positive impact of mechanical vibrational energy on the curing process. Electrical impedance monitoring was used as a validation technique.

These promising results target: (a) improving the continuous monitoring of the local curing status, and (b) using the energy of guided ultrasonic waves to accelerate the curing time and to direct inhomogeneities, such as voids, away from critical structural regions with the aim of improving the overall quality of the cured material.