• friction stir spot welding
• solid state joint
• helmholtz zentrum hereon
• fatigue
• residual stress

Refill Friction Stir Spot Welding (refill FSSW) is a solid-state process that shows great potential to be a substitute for single-point joining processes like riveting. The main objective of this study is to investigate and the mechanical behaviour of joints obtained by refill FSSW and adhesive sealant. Overlap joints in aircraft structures require the use of sealants for corrosion protection reasons, but using a sealant with an adhesive function allows to increase the mechanical properties of the joint. The result of this study supports the European project DAHLIAS (Development and Application of Hybrid joining in Lightweight Integral Aircraft structures) which involves three different countries with several research institutes and companies; Helmholtz Zentrum Hereon holds the role of coordinator. The objectives of the study can be summarized as follow:
- Characterize refill FSSW joints with adhesive sealant in terms of microstructure and residual stress;
- Investigate the static and dynamic mechanical properties of the joint and failure mechanisms;
- Optimise, in terms of mechanical properties, the joint design;
- Investigate fatigue initiation mechanism;
- Characterize the residual stress field in multi-spot joints;
- Understand the stress and strain field in different joint configurations;
- Develop a simple numerical model to evaluate different joint configurations in terms of stress distribution;
- Produce two full-scale demonstrators of aeronautical structures.