Material Adapted Method for the Repair of Curved Thermoplastic Composite Structures by Induction Welding of Patches

<div class="section abstract"><div class="htmlview paragraph">Thermoplastic fiber-reinforced polymer composites (TPC) are gaining relevance in aviation due to their high specific strength, stiffness, potential recyclability and the ability to be repaired thanks to their meltability. To maximize their potential, efficient repair methods are needed to maintain aircraft safety and structural integrity. This article introduces a novel repair technique for damaged TPC structures, involving the joining of a repair patch with induction welding using a susceptor material. The susceptor consists of a material with high electrical conductivity and magnetic permeability and therefore reacts stronger to the electromagnetic field than the composite, even if the composite is carbon fiber based. I. e. the thermal energy is specifically concentrated in the repair area. In this study, the susceptor was placed on the patch and also in the welding zone.</div><div class="htmlview paragraph">The repair process begins by identifying and preparing the damaged area, followed by precise scarfing. Care is taken to ensure that the surrounding material remains intact and that an exact stepped structure is created, which enables an optimal bonding with the patch to be used. The customized patch, which fits perfectly in terms of shape and material to the area to be augmented, is then inserted into the structure. Induction heating melts the thermoplastic matrix to join the patch with the structure using a flexible induction mat. The repair process is monitored using thermocouples to ensure even heat distribution, while pressure is maintained through a vacuum bag. The vacuum bag ensures a uniform pressure distribution even on complex curved structures.</div><div class="htmlview paragraph">This adaptable repair method can handle individual damages. It was tested on flat carbon fiber-reinforced polyphenylene sulfide (CF-PPS) structures, showing repairs with nearly 70 % of the original performance for copper mesh susceptors. Optical tests of the specimens confirmed a bonding zone with minimal defects. Overall, this method offers a material-compatible solution for TPC repair in future aviation, advancing aerospace maintenance and offering significant potential for future industry use.</div></div>