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

Last modified: 2023-05-15


Reduction of the structural weight of the aircraft structure and saving the manufacturing cost of the aircraft structure are important in order to develop the competitive aircraft. Manu procedure 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's and applied to automobiles, trains, rockets, and ships. It is expected to be applied to commercial aircraft primary strucutres as an alternative to riveting in order to reduce production costs and weight.

In addition to the evaluation of mechanical property such as Young's modulus, elongation, yield and ultimate stress of the frinction stirred (FSWed) joint, the crack growth behavor in FSWed joint and its fracture origin have to be evaluated in order to comply with the damage tolerant requirement. The corrosion resisitance of the joint also is imperative feature and the corrosion damage under corrosive environmental and the fatigue strenght for pre-corroded specimen has to be evaluated, in order to be evaluated, in addition to the evaluateion of its fracture.

Mechanical test of the FSWed joint of 2024-T3 aluminum alloy are conducted in order to evaluate its static and fatigue property. The origin of fracure and the fatigue crack gorwth behaviour of the joint are identified by observation of the fracture surface. The fatigue crack growth of non-through crack for fatigue specimen are eavluated 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 speicmen 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 evalutaed.

Further, fatigue crack growth behavior of the WFDed joint

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