PhD Supervisor: Pedro Miguel Guimarães Pires Moreira (FEUP)
Thesis Topic: The ultimate aim of this thesis is the development of a joining technique using both adhesive bonding and friction stir welding. These joints would have good static and fatigue properties, and would be applicable in a large array of structure types (aircrafts primary and secondary structures, automotive structures, etc.). The use of these joints would allow more flexible structural design, lightweighting and high performance. A long with this goal this thesis also aims at instrumenting the developed joints for structural health monitoring.To fulfil these goals the following objectives have to be accomplished:
- Development of a fabrication methodology for hybrid friction stir weldbonded joints, including designing
- moulds and clamping systems, FSW tool geometries, procedures, etc.;
- Characterization of the adhesive mechanical properties;
- Selection of the correct process parameters for the fabrication of sound joints;
- Mechanical characterization of the hybrid joints, including static mechanical testing, metallographic
- analysis, and dynamic response properties assessment;
- Finite element simulation of the developed joints;
- Fatigue strength assessment of the developed joints;
- Comparison between the developed joints and adhesive bonded joints and friction stir welded joints,
- regarding all the studied properties;
- Implementation of fibre Bragg grating (FBG) sensors for structural monitoring;
- Strain monitoring using the embedded FBGs during manufacturing process.
It is expected that this thesis will be a significant contribution to the durability of lightweight stiffened structures, through the development and characterization of a novel joining technique, friction stir weldbonding. It is also foreseen that the implementation of sensing capabilities in the developed joints will improve the structural monitoring of safety critical structures. In order to achieve these aims, work and innovation in different but inter-related fields will be carried out:
- Fabrication methodology for friction stir weldbonded joints will be developed;
- Optimization through finite element analysis using a cohezive zone elements to model crack initiation
- and propagation, as well as an experimental programme based on the Taguchi method;
- Static mechanical testing will be performed, and the dynamic response of friction stir weldbonded joints
- characterized through frequency response functions (natural frequencies and damping ratios), will be
- A new technique to insert FBG sensors during the adhesive bonding curing process will be developed.
Measurements will be performed during the joining process in order to analyse the residual stresses induced by the manufacturing process, which is a novel result in itself. Using the pre-installed fibres, monitoring of the joint during the testing programme will also be possible. The failure initiation moment will be analysed;
- Fatigue strength of the developed joints will be assessed through testing under constant amplitude loading;
- Structural health monitoring during the fatigue strength testing using the embedded FBGs.