Nature-inspired aerospace hybrid structural joint concepts realised by additive manufacturing

The need to join metallic to composite parts is unavoidable in many complex structures such as modern aircraft. Joints are commonly a weak point in any structure, and this is exacerbated by the use of dissimilar materials. Advanced manufacturing processes such as selective laser melting (SLM) offer limitless flexibility and potential for innovative design concepts, but today’s hybrid joints are still designed using conventional manufacturing techniques. The aim of this research is to mimic the way biological systems use a hierarchy of different techniques to join dissimilar materials. Carbon-epoxy laminates are co-cured to an SLM-manufactured metallic part, with three joining techniques investigated at different scales: 1) inherent SLM-metal roughness; 2) crack deflection surface features and 3) z-pins through the composite thickness.<br><br>The adhesion properties of all three levels are characterised using experimental, analytical and numerical analysis. At the micro scale, it was found the intrinsic micro surface morphology of as-built SLM components allows as-built SLM component to be effectively bond with composite material without any additional surface treatment process. Macro features were found to increase the fracture toughness of the joint as the crack deflects around the macro features, which increase in the crack path length and the shift from pure mode I to mixed-mode crack growth. Mechanical interlocking effect is also evaluated and critical aspect length/diameter aspect ratio is established, correlation of single and multi-pin joint behaviour is illustrated and analysis methodology is produced to design and optimise hybrid joint. Further, all practical industrial working conditions of hybrid joint in term of mode mix loading, constraint type, pin features are characterised experimentally and numerically at different length scale. Finally, high fidelity numerical model was developed to predict the damage process and load vs displacement response during pin pull-out process. The results correlate well with experimental observation.<br><br>The research outcomes of this PhD made significant contribution to the body of knowledge for hybrid metal-composite joint and propose an innovative bio-inspired hierarchical joining techniques capable of replacing current joining standard of light weight structure using additive manufacturing method.