System for in-situ dielectric and calorimetric measurements during microwave curing of resins

The use of new materials is of great interest for science, research and industry. Fiber composite materials such as carbon fiber or glass fiber composites find due to their lightweight potential, as well as their mechanical and physical features increasing application in aerospace engineering, the automotive industry and the general engineering. The main obstacle to these materials is the difficulty of manufacturing with long cycle times and high energy consumption. Therefore, it is of great interest to find new approaches, which accelerate the production of fiber composites, while making it more energy-efficient. Here, the microwave curing is a promising technology for the preparation of fiber-reinforced composites, as it is faster and more cost-effective, because it is based on the volumetric heating of the material. This motivated the development of various microwave systems and processes. Nevertheless, for a successful system and process design the detailed knowledge of the dielectric properties of materials is mandatory. Therefore, a system for in-situ monitoring of curing processes of thermoset resins under microwave heating was developed. The main function of the measurements instrument is the dielectric characterization of resins based on the cavity perturbation technique. Here, the electromagnetic source used for dielectric characterization of the material under test is used for dielectric heating at the same time. The cavity operates at 2.45 GHz in the TE₁₁₁ mode. It has an unloaded quality factor of 11500. In addition, a calorimetric analysis of the exothermal curing process is envisaged.