Application of Microwave Heating for Adhesive Joining

In conventional joining of composite materials and sandwich structures, reductions in processing time are limited by inefficient heat transfer. In conventional processing the thermal energy must diffuse through the composite layers to heat the joint interface and cure the thermosetting adhesive, and this outside-in process of heating results in excessive processing times and wasted energy. The purpose of the current work is to examine microwave heating as an alternative to conventional heating for joining of composite structures. Through proper material selection, microwaves are able to penetrate the substrate materials and cure the adhesives in-situ. Selective heating with microwaves is achieved by incorporating interlayer materials that have high dielectric loss properties relative to the substrate materials. In this study, a processing window for elevated temperature curing of an epoxy paste adhesive system (HYSOL EA 9359.3) was developed and composite joint systems were manufactured using conventional and microwave techniques and tested in shear. Microwave curing resulted in both enhanced shear strength and less scatter in experimental data.