Colloquia

Summary

The latest generation of commercial aircraft consist out of composites and metals following the ‘right material in the right place’ design principle. The industry is interested in reversible joining of metal – thermoplastic composites to increase production rates and allow for recycling. This research investigates the use of resistance heating for reversible joining titanium (Ti-6Al-4V) to carbon fibre reinforced low-melt polyaryletherketone (CF/LMPAEK).

Experimental methods are used to determine the processing window and control the process. In order to maximize the single lap shear strength, various interface temperatures and interface design variations are considered. Interface design variations concern surface treatments of the titanium and varying interlayer materials between the substrates. Five interface design variations are considered: untreated (1), pin reinforcements on the titanium substrate (2), laser treatment on the titanium substrate (3), polyetherimide (PEI) interlayer material (4), and the exclusion of electrical insulation interlayers (5). All titanium substrates are created by means of additive manufacturing. Apart from single lap shear testing; micrograph cross-sections for untested samples, the failure mode, and failure behaviour are compared for the temperature and design variations. The quality of the resistance welded joints is evaluated by comparing with autoclave co-bonded hybrid joints. Next to the experimental work a 3D finite element model is constructed to characterize the heating behaviour of the resistance welding setup. Disassembly of hybrid joints by resistance heating focuses on determining the influence of temperature on the single lap shear strength and failure behaviour for various interface design variations.

Micrograph cross-sections and failure mode analyses indicate that a high joint strength depends on both the polymer material and the surface of the titanium substrate. The pin reinforcements, PEI interlayer material, and laser treatment design variations result in significantly stronger resistance welded and autoclave co-bonded joints compared to the untreated case. On the other hand, the interface temperatures chosen do not significantly influence the strength or failure modes. Reversible joining via resistance heating is feasible with minimal force input for the untreated, PEI interlayer and laser treatment design variations. PEI polymer interlayers can be disassembled at lower temperatures compared to LMPAEK. Further developments of the disassembly setup are required to minimize damage to the thermoplastic substrate and resistance heating element.