Repair of thermoplastic composite structures by induction heating

为了在下一代商用飞机中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。热塑性复合材料与更常规的热固性复合材料相比具有一些重要的优点，其中它们能够被再加工，这允许它们通过焊接（与机械紧固或粘合剂结合相反）连接。 感应焊接被认为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流，其产生与电流相同频率的时变磁场。当电导体放置在线圈附近时，感应出涡电流，通过焦耳损失产生热量。该原理用于焊接热塑性复合材料。在这种情况下，电磁或导电感受器可以放置在待焊接的两个粘附体之间，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增加，并且当达到预定的处理温度时，电流被切断，并且焊接界面在压力的施加下冷却，从而产生焊接接头。在目前的研究计划中，我建议进一步发展这一过程，并使用它来修复热塑性复合材料结构后，他们已经损坏。实际上，修复方法是针对更传统的热固性复合材料而开发的，但从未针对热塑性复合材料开发过，这限制了该行业更换受损部件而不是修复它们，从而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，更有效的，将用于修复焊接接头的纳米复合材料的电阻器，（2）通过利用感应加热的损坏的碳纤维热塑性复合材料结构的修复方法的发展和（3）的多物理模型的感应加热的发展，以预测修复过程。 据信，这一创新的研究计划和高素质人才的相关培训将使加拿大航空航天业受益，并确保其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.