Repair of thermoplastic composite structures by induction heating

为了在下一代商务和商用飞机上成功实现成本和重量的降低，必须开发新的先进结构材料和工艺。在过去的十年中，一类纤维复合材料，即热塑性复合材料，在航空航天工业中不断获得市场份额。与传统的热固性复合材料相比，热塑性复合材料有一些重要的优点，其中包括它们的再加工能力，这使得它们可以通过焊接连接（而不是机械紧固或粘合剂粘合）。感应焊是一种很有前途的热塑性复合材料焊接工艺。感应加热是基于在线圈中循环的高频交流电，产生与电流频率相同的随时间变化的磁场。当导体放置在线圈附近时，就会产生涡流，通过焦耳损耗产生热量。这一原理被用于热塑性复合材料的焊接。在这种情况下，可以在两个待焊附着物之间放置一个电磁或导电的感受器，以使焊接界面处的加热局部化。当感受器加热时，位于其附近的聚合物的温度升高，当达到预定的加工温度时，电流被切断，焊接界面在压力的作用下冷却，从而形成焊接接头。在目前的研究计划中，我建议进一步发展这一工艺，并将其用于热塑性复合材料结构损坏后的修复。实际上，修复方法是针对更传统的热固性复合材料开发的，但从未针对热塑性复合材料开发过，这限制了行业更换损坏的部件而不是修复它们，这带来了相关的负面成本和环境影响。通过建模和实验工作，我们打算进一步发展感应加热工艺，并将其应用于热塑性复合材料结构的修复。提出了三个研究方向：(1)开发新的、更高效的纳米复合材料感受器，用于焊接接头的修复；(2)开发利用感应加热修复受损碳纤维热塑性复合材料结构的方法；(3)建立感应加热的多物理场模型，以预测修复过程。相信这一创新的研究项目和高素质人才的相关培训将使加拿大航空航天工业受益，并确保它准备好应对热塑性复合材料的独特挑战，并在全球市场上竞争。

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.