Co-consolidation of titanium-C/PAEK joints: an investigation into the interfacial performance governing mechanisms

Fastener free metal-carbon fibre reinforced thermoplastic composite hybrid joints show a potential for application in aerospace structures. In comparison with fastened hybrid joints, fastener free hybrid joints exhibit advantages in terms of joint weight reduction and a more uniformly distributed stress field within the joint. The metal-thermoplastic composite co-consolidation technique shows potential for manufacturing those fastener free hybrid joints in an economic manner. In this technique, the metal parts are essentially co-consolidated with fibre reinforced thermoplastic composite prepreg. The thermoplastic resin present in the prepreg is thus used for bonding and no additional adhesives are employed. However, there is far less understanding of the performance of metal-thermoplastic composite interfaces as a crucial factor affecting the strength of the entire co-consolidated metal-thermoplastic composite hybrid joint. The performance of the metal-thermoplastic composite interface is governed by a variety of factors, which are promoted by introducing various bonding mechanisms: mechanical interlocking between metal and thermoplastic composite, physical attraction between metal and thermoplastic composite, and chemical bonding between metal and thermoplastic composite. In addition, the thermal residual stress in adherends generated during the consolidation process can impair the interfacial performance. Therefore, with a view to optimising the performance of the interface, the investigation of the effectiveness of these governing factors is significant. The metal-thermoplastic composite hybrid joints studied in this thesis employ grade 5 titanium (Ti-6Al-4V) as the metal component, while the composite components are from the carbon fibre reinforced polyaryletherketone (C/PAEK) family. In this thesis, the Ti-C/PAEK interfacial performance and the governing factors between titanium and C/PAEK are investigated in the following aspects: • Suitable experimental approaches to evaluate the Ti-C/PAEK interfacial performance, namely mandrel peel test, have been developed and critically assessed. • The mandrel peel test is subsequently employed to evaluate the effectiveness of factors governing the Ti-C/PAEK interfacial performance. Furthermore, the bonding mechanisms activated by these factors are elaborately investigated by experimental approaches. • The aforementioned experimental approach shows that the mechanical interlocking between titanium and thermoplastic composite is an important factor in the interfacial performance. Therefore a theoretical study, including analytical and numerical models, is carried out to enhance the understanding of the effectiveness of mechanical interlocking on the interfacial performance. In order to apply the co-consolidation technique in practice, the effectiveness of the interfacial performance governing factors on the strength of co-consolidated Ti-C/PAEK joints is further studied. Finally, a guideline for fabricating Ti-C/PAEK hybrid joints by the co-consolidation technique, focusing in particular on optimising the Ti-C/PAEK interfacial performance of the hybrid joints, is proposed at the end of this thesis.