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The fatigue behavior of aluminum-zinc-magnesium (Al-Zn-Mg) alloy fillet-welded joints was analyzed in fracture mechanics terms. Basic crack propagation data were obtained with −2 ⩽ R ⩽ + 0.5 and correlated using formulas in the literature and, more successfully, in terms of ΔKeff, based on the results of crack closure experiments. The form of the da/dN versus ΔK relationship was influenced by the specimen geometry. A fracture mechanics analysis of the fatigue life of Al-Zn-Mg alloy fillet welds based on the da/dN versus ΔKeff relationship indicated that the weld toe was less severe from the fatigue viewpoint than the same region in a steel fillet weld. This was compatible with the fact that metallurgical examination of Al-Zn-Mg alloy fillet welds has failed to reveal toe defects similar in magnitude to those which act as fatigue crack initiators at the toes of steel fillet welds. The analysis showed that the fatigue life obtained from the Al-Zn-Mg alloy weld could be predicted on the basis that defects only one tenth the size of those observed in steel were present. Fatigue failure from the weld root in a cruciform joint was also analyzed and the optimum weld design, which gives an equal chance of failure from the root and toe, was determined. The analysis was supported by fatigue test results. Comparison with results obtained for steel added confirmation to the finding that if toe defects are present in Al-Zn-Mg alloy welds, they are smaller than those in steel.
fatigue tests, weldments, aluminum alloys, crack propagation, fatigue (materials), fracture mechanics, fillet welds, defects, cracking, initiation, durability, design
Head of Fatigue Laboratory, The Welding Institute, Cambridge,
Principal scientific officer, Military Vehicles and Engineering Establishment, Christ-church, Dorset,