On the influence of joining processes on the vibration of structures

The joining of new and dissimilar materials in the transportation sector, to meet the demands for lighter structures, requires the use of alternative joining processes. However, it is not clear how different types of structural joints compare in terms of their contribution to the vibration and damping of structures. The present work aims to provide a comprehensive experimental and numerical analysis on the contribution of three structural joints – butt friction stir welding, single lap adhesive joint and hole hemmed joint – to the vibration and damping of two joined aluminium sheets. For this purpose, experimental analysis is performed to study the free-free vibration of the three structural joints. In addition, finite element models are developed to better understand the behaviour of these joints and discuss the challenges of the numerical modelling procedure. The first four natural frequencies, experimentally obtained for each structure, suggest that the adhesive joint has significantly higher natural frequencies, due to the thickness increase at overlap, while the hole hemmed joint presents the most significant contribution to damping, owing to sliding at the overlap region. The numerical models show a very good agreement with the experimental results in terms of the natural frequencies and mode shapes, with simple modelling providing accurate results. In conclusion, the main findings are that the adhesive joints allow for a stiffer structure, with the natural frequencies increasing with the overlap dimension, while hole hemming enhances damping. The butt-butt friction stir welding has a small effect on the structural behaviour, showing a similar dynamic stiffness and damping when compared to a solid sheet of the same dimension.