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Evaluation of crack growth behavior in aluminum alloy joined by the friction stir welding
Takao Okada

Last modified: 2023-05-14



Reduction of the structural weight of the aircraft structure and saving of the manufacturing cost of the aircraft structure are important in order to develop the competitive aircraft. Many procedures such as laser beam welding, friction stir welding (FSW) and 3D printing, and application of the composite materials have been researched in many years for the issues. Friction stir welding is developed in 90’ and applied to automobiles, trains, rockets, and ships. It is expected to be applied to commercial aircraft primary structures as an alternative to riveting in order to reduce production costs and structural weight.

In addition to the evaluation of mechanical property such as Young’s modulus, elongation, yield stress and ultimate strength of the friction stir welded (FSWed) joint, the crack growth behavior in FSWed joint and its fracture origin have to be evaluated in order to comply with the damage tolerant requirement. The corrosion resistance of the joint also is also imperative feature and the corrosion damage under corrosive environment and the fatigue strength for pre-corroded specimen has to be evaluated, in addition to the evaluation of its fracture origin.

Mechanical test of the FSWed joint of 2024-T3 aluminum alloy are conducted in order to evaluate its static and fatigue property. The origins of fracture and the fatigue crack growth behavior of the joint are identified by observation of the fracture surface. The fatigue crack behavior of non-through crack for fatigue specimen are evaluated experimentally and numerically. The corrosion test of the FSW 2024-T3 aluminum alloy is conducted for four immersion period. The morphology of the pre-corroded surface is measured and the size of the corrosion pits are obtained. The corroded specimen is also used for the fatigue test. In addition, corrosion pit is assumed as the initial crack and fatigue crack growth life of the pre-corroded specimen required for the crack to span the specimen width is analytically evaluated.

Further, fatigue crack growth behavior of the FSWed joint of 2024-T3 aluminum alloy are conducted using MT specimen, in order to evaluate the effect of residual stress on the fatigue crack growth. The obtained crack growth behavior is compared with the numerical and analytical results