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

Thermoplastic fiber-reinforced polymer composites (TPCs) are gaining importance in aviation due to their high strength, stiffness, and recyclability. 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 insertion of a repair patch with 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 it is carbon fiber based. This means that the thermal energy is specifically concentrated in the repair area. The susceptor can be placed on the patch surface or in the welding zone. The 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 corresponds exactly in shape and material to the area to be augmented, is then inserted into the structure. The patch’s stepped structure increases contact and enhances strength. Induction heating melts the thermoplastic matrix to fuse the patch with the structure. The repair process is monitored using thermocouples to ensure even heat distribution, while pressure is maintained through vacuum sealing. This adaptable repair method can handle both small and large damages. It has been tested on carbon fiber-reinforced polyphenylene sulfide (CF-PPS) structures, showing repairs with 80% of the original strength and stiffness. Optical tests confirmed a uniform bonding zone with minimal defects, ensuring strong bonding. Overall, this method offers an efficient, material-compatible solution for TPC repair in aviation, advancing aerospace maintenance and offering significant potential for future industry use.