Repair of thermoplastic composite structures by induction heating

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To successfully achieve cost and weight reduction in the next generations of business and commercial airplanes, new advanced structural materials and processes must be developed. In the past decade, a class of fibre composite materials, i.e., thermoplastic composites, have been constantly gaining market share in the aerospace industry. Thermoplastic composites have some important advantages over the more conventional thermosetting composites among which their ability to be re-processed which allows them to be joined by welding (as opposed to mechanical fastening or adhesive bonding).Induction welding was identified as a promising welding process for thermoplastic composites. Induction heating is based on a high-frequency alternating electrical current circulating in a coil, which generates a time-variable magnetic field of the same frequency as the current. When an electrical conductor is placed in the vicinity of the coil, eddy currents are induced, creating heat by Joule losses. This principle is used to weld thermoplastic composites. In this case, an electromagnetic or electrically-conductive susceptor may be placed between the two adherends to be welded to localize heating at the weld interface. When the susceptor heats up, the temperature of the polymer located in its vicinity increases and when a pre-determined processing temperature is reached, the current is switched off and the weld interface cools down, under the application of pressure, resulting in a welded joint. In the current research program, I propose to develop further this process and use it to repair thermoplastic composite structures after they have been damaged. In effect, repair methods were developed for the more conventional thermosetting composites but never for thermoplastic composites, constraining the industry to replace the damaged components instead of repairing them, with associated negative cost and environmental impacts.Through modelling and experimental work, we intend to develop further the induction heating process and apply it to the repair of thermoplastic composite structures. Three research axes are proposed: (1) the development of new, more efficient, nanocomposite susceptors which will be used for repairing welded joints, (2) the development of repair methods for damaged carbon fibre thermoplastic composite structures by taking advantage of induction heating and (3) the development of a multi-physics model of the induction heating in order to predict the repair process.It is believed that this innovative research program and the associated training of highly qualified personnel will benefit the Canadian aerospace industry and ensure that it is ready to address the unique challenges of thermoplastic composites and compete in the global market.