Friction-based joining of metal-composite multi-material structures: the future is hybrid

One of the hot topics in the development of aircraft lightweight structures is metal-composite material combinations. Lightweight and hybrid structures are gradually being selected in the aviation industry to reduce fuel consumption and emissions. There is an enormous potential for further exploiting this knowledge area in the next decades, not only for future commercial airplanes and cars but also in wind energy and in civil engineering. Metal-composite hybrid structures are characterized by the presence of solid interface(s), normally with a sharp gradient in properties, meaning high interfacial heterogeneity. The intrinsic dissimilarity of metal-polymer composite hybrid structures spawns an engineering challenge for innovating approaches in joining technology. Friction-based joining (FBJ) of polymer-metal hybrid structures is an emerging research field, previously introduced in other works of the authors. FBJ processes usually feature short cycle-times, little to no pre- and post-treatment of joined parts, and environmental / user-friendliness. Moreover, the base material microstructure is changed to a lesser extent, as heat development is controllable. Therefore, joints present good mechanical performance.

This work addresses the current progress of several new, prize-winning friction-based joining technologies for metal-composite structures: Friction Riveting, Friction Spot Joining, Friction-based Staking and Ultrasonic Joining. These innovative joining techniques are studied and optimized based on the fundamentals of Materials Science and Manufacturing Engineering. Polymer science and metallurgy combined with Design of Experiments and statistical analysis are applied to evaluate the correlations between joining process parameters, microstructure, materials properties and mechanical performance. Case-study examples of aircraft material combinations will be presented for the joining technologies mentioned above.