Damage tolerance of refill friction stir spot weld application for the aircraft industry
Refill Friction Stir Spot Welding (Refill FSSW) is a solid-state process technology that is suitable for welding lightweight materials in similar or dissimilar overlapped configuration. It has proven to be a very promising new joining technique; especially, for high strength aluminum alloys, which h...
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| Format: | Abschlussarbeit Buch |
| Sprache: | English |
| Veröffentlicht: |
Hamburg
2019
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| Zusammenfassung: | Refill Friction Stir Spot Welding (Refill FSSW) is a solid-state process technology that is suitable for welding lightweight materials in similar or dissimilar overlapped configuration. It has proven to be a very promising new joining technique; especially, for high strength aluminum alloys, which has presented large advantages when compared to conventional welding processes. Currently, Refill FSSW is recognized as a potential alternative for riveted structure; it allows an increasing of the manufacturing cost effectiveness owing to sensible cost reduction and structural efficiency. The main aim of this work is to study the mechanical behavior and crack propagation in joints produced by Refill FSSSW. The study is focused on the application of the damage tolerance design philosophy in integral structures produced by Refill FSSSW in aluminum alloy AA2024-T3. Up to now the process development and the mechanical performance study has been mostly empirical. Thus, a transition to a science-based approach is highly necessary. The work presented here was conducted to stablish a relationship of experimental investigation and a set of numerical models that can be used for design optimization and fatigue crack growth analysis. Beforehand, the welded joints were assessed mechanically and metallurgically in order to investigate the mechanism and the optimization of the process parameters (rotation speed, welding time and plunge depth) in terms of quasi-static loading and fatigue loading. This investigation has assisted the development of the structural numerical models, where two structural models have been developed to study the design optimization. The first model covers the stress analysis, load transferred by friction, stress concentration and peak stress location; it was built considering the structural and cohesive approach. The second numerical model considers the embedded approach; it can be used for parametric studies with good accuracy. Then, the design optimization was developed considering the distances: number of spot welds rows, spot weld row spacing, spot weld pitch in row and distance of the spot weld from the sheet edge. The developments of the distances were performed considering its performance in quasi-static and fatigue loading. A fractography analysis at various fracture modes has been performed. This is necessary in order to understand and described the crack propagation according the fracture mechanics. Then, a numerical model has developed and calibrated in order to obtain stress intensity factors for the cracks described previously. The numerical model has been built with the eXtended Finite Element Method. Finally, the thesis deals with crack propagation and residual strength of Refill FSSW in thin panels for aircraft fuselage applications. |
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| Beschreibung: | Sonstige Körperschaft: Technische Universität Hamburg, Institut für Werkstoffphysik und Werkstofftechnologie |
| Beschreibung: | XII, 136 Seiten Illustrationen, Diagramme |