(44i) Targeted Heating and Curing of Adhesives for Bonding Multi-Material Composites Using Radio Frequency Fields

Carbon nanoparticles are known to produce a strong, rapid heating response in the presence of a radio-frequency (RF) electromagnetic field. This exceptional property can be used to selectively cure nanocomposite thermoset adhesives for bonding plastic-plastic and metal-metal substrates, without warping or distortion of the composite structure. This approach of selective heating is particularly of great interest to the automotive industry, where multi-material bonding is ubiquitous. We employed non-contact RF applicators to generate an electric field through a carbon-black-loaded adhesive for bonding plastic-plastic substrates, which then volumetrically heats and cures. Because this heat was selectively generated in the adhesive, plastic substrates maintained temperatures lower than the curing temperature of the adhesive. Plastic substrate temperatures as low as 53 °C were observed while the adhesive cured at a target temperature of 85 °C; in contrast, plastic substrate temperatures exceed the adhesive temperatures when using conventional heating methods, such as IR lamps or ovens. The strength of cure was confirmed by mechanical testing and lap shear strengths of RF-cured adhesive joints was measured to be 3.26 MPa. The RF technology has shown promise for bonding metal-metal substrates as well. Using direct-contact RF applicators, where the metal substrates act as RF applicators, a strong electric field is generated between the metal substrates, that heats and cures the nanofiller loaded adhesive. This method of targeted heating of adhesive can mitigate distortions and residual thermal stresses caused by oven curing of composite systems consisting metallic components. Targeted heating and curing of adhesives using RF fields can be envisioned as a viable method for joining dissimilar materials (ferrous metals, nonferrous metals, fiber-reinforced plastics, and others). This would enable high performance and flexible joints while eliminating the weight and cost of fasteners associated with mechanical joining techniques.