Effect of incident microwave frequency on curing process of polymer matrix composites

Abstract

Microwave assisted curing of aerospace and structural polymer matrix composites depends on several factors such as dielectric properties of the curing substrate, type of tooling used, thickness of the composite part, kind of applicator chosen and so on but one of the most important factors is the frequency of radiation used for the purpose of curing. Majority of the work reported on microwave curing of polymer composites is restricted to the commonly utilized frequency of 2450 MHz, whereas 915 MHz frequency is extensively employed chiefly for food processing and wood drying applications. This paper evaluates the potential of 915 MHz frequency for curing polymer matrix composites.2 mm thick glass-epoxy composite laminates were prepared using bi-directional glass fiber reinforced epoxy resin system. These composites were then cured in three different ways: microwave curing with 915 MHz as incident microwave frequency; microwave curing with 2450 MHz as incident microwave frequency and conventional thermal (oven) curing. Comparison between microwave and thermal cure process times as well as energy consumption revealed the significant time and energy savings realized by microwave curing. Further, mutual comparison of the cured laminates was drawn in terms of attainment of lamination quality, glass transition temperature and mechanical properties. The results obtained showed that the 915 MHz microwave cured laminate had superior inter-laminar shear strength (ILSS) and flexural strength as compared to 2450 MHz microwave cured and thermally cured laminates. This, in essence, implies that incident microwave frequency plays a crucial role in designing cure process parameters for polymer matrix composites.