Objectives

In order to address the knowledge gaps identified by the Clean Sky 2 programme topic adressed, the following objectives have been defined for this project:

Conduct a systematic process parameter study aiming at the definition of the effect of process parameters on defect formation, mechanical properties and corrosion resistance of the joints for similar and dissimilar configurations of the alloys AA 2024 and AA 7075. This study shall allow for the definition of process parameter fields for optimum properties, corrosion behaviour and absence of defects. These resuts shall be stored on a database and compiled in the form of a process procedure catalogue.
To develop adhesive sealant technology that will include surface pretreatment technology, adhesive promoter and low-density sealant with high adhesion properties. The adhesive sealant technology should provide a chemical resisting layer that fills the gap of a joint, protecting the inner surface from corrosion. The adhesive sealant technology to be developed as part of this project must fulfil the current standard requirements for sealanst imposed by the aeronautical industry, which should not be affected by the thermal load resulting from the joining process.
To optimize the welding process parameters for joining of similar aluminium alloy 2024 and 7075 with adhesive sealant bond (hybrid joints) resulting in optimum mechanical performance
To compare the mechanical performance of RFSSW with conventional joining technologies (fusion welded, resistance welded, adhesive bonded and riveted joints) in terms of tensile, fatigue and fatigue crack propagation behaviour. In order to conduct a meaningful comparison it is however necessary, to establish a spot placement strategy for the RFSSW process, since presently there are no design guidelines for this process. For this purpose finite element models will be optimised and used to generate essencial geometrical information such pitch and edge distances.
To characterize and describe the defects and inconsistencies in RFSSW and based on that develop an understanding on the defect formation mechanisms. Establish the effect of process parameters and joining procedures on defect formation and the effect of defects on the mechanical behaviour of RFSSW joints.
Select appropriate NDT methods to detect the identified flaw types and develop a process monitoring methodology for online control of RFSSW.
To congregate the individual efforts in this project to produce two demonstrators: flat structure and fuselage structure, whereby RFSSW joints will be produced with optimum process parameters, in similar and dissimilar configurations combined with the use of adhesives/sealants. The spot welds will be placed according to damage tolerance criteria. The respective fixtures will be designed, manufactured and tested in order to ensure a precise and defect free placement of spot joints.