Adhesive joining of carbon fibre reinforced polymer (CFRP) is cumbersome due to the careful surface preparation required and multiple validation steps to certify adhesion quality. Further these joints are often supplemented by mechanical fastenings add weight whilst also localising bearing stress. As an alternative technique, CFRP parts can be functionalized with thermoplastic surfaces during manufacture to enable cost-effective welding of composite structures. In the process of manufacturing the CFRP, curing an epoxy resin in the presence of the functionalising thermoplastic polymer can lead to local dissolution of the latter in the epoxy, followed by a reaction-induced phase separation. This results in a thermosetting-thermoplastic interphase featuring gradient concentrations and a multiphase morphology, which promotes load transfer between the thermosetting matrix and the thermoplastic joint. The aim of the work presented in this paper was to investigate interphase formation between high-Tg epoxy and polyetherimide (PEI) at different curing temperatures. The morphology was characterised using scanning electron microscopy and the composition of the interphase was quantified through Raman spectroscopy. The curing experiments indicated that temperature has a significant effect on the interphase morphology and led to two different biphasic morphologies which generally increased in size with increasing curing temperature. This suggests that the size of the gradient interphase can be tailored through the curing process, which is as a fundamental step in optimising the structural performance of welded joints with PEI-functionalized epoxy-based CFRPs.@en

Passive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. By utilisation of compression flange buckling, the in-plane stiffness can be tuned to design beams with contrasting pre-buckling and post-buckling bending stiffness. The investigated concept is experimentally validated using a thin-ply laminated composite four-point bending beam, which is designed to experience compression flange buckling in the span with constant moment. The bending stiffness was reduced by more than 41% after the onset of buckling which shows the effectiveness of compression flange buckling for non-linear bending compliance.@en

Passive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. This paper presents a passive spanwise bending shape-adaption concept for highly loaded wing-like structures based on local buckling of the compression flange at a prescribed external bending moment. Buckling reduces the in-plane stiffness of the compression flange and thus yields a beam design with a high prebuckling and a low postbuckling bending stiffness. The investigated concept is experimentally validated using a composite four-point bending beam, which is designed to experience compression flange buckling between the load introductions. The point of buckling is at 374.80 Nm, and ultimate failure occurred in the experiment at 524 Nm, which results in a postbuckling range of 149.2 Nm. The bending stiffness was reduced by more than 41% after the point of buckling which shows the effectiveness of compression flange buckling for nonlinear bending compliance. This proof of concept has demonstrated for the first time, that compression flange buckling is a viable structural concept for highly loaded composite beam structures to achieve nonlinear bending compliance.@en