Fatigue Crack Propagation in Aluminum-Zinc-Magnesium Alloy Fillet-Welded Joints

Abstract

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.

Ermüdungsfestigkeit

“…Die Rückrechnung auf kleine fiktive Anfangsrisse nach der Rißfortschrittsgleichung unter Verwendung von DK-Werten, wie sie von Maddox [1707][1708][1709] oder Hobbacher [1700,1701] für Schweißverbindungen vorgeschlagen wurde, muß dagegen als weniger geeignet angesehen werden, weil sie dem tatsächlichen Kurzrißfortschrittsverhalten auch nicht näherungsweise entspricht.…”

Fatigue Testing and Analysis of Aluminum Welds under In-Service Highway Bridge Loading Conditions

“…Large databases of test results have been used to establish the current fatigue design provisions for aluminum welds. Fatigue test results on specific weld details have been reported in several studies (Maddox and Webber 1977;Maddox 1995;Mazzolani and Grillo 1995). Others have compiled test results and discussed the development of the current fatigue design provisions (Menzemer and Fisher 1995;Jaccard et al 1995;Soetens et al 1995;Maddox 2003), which commonly employ fatigue-resistance (S-N) curves and the detail category approach.…”

Fatigue Properties of 6061-T6 Aluminum Alloy T-Joints Processed by Vacuum Brazing and TIG Welding

“…21) Recent work has shown that the thickness effect depends on the overall proportions of the welded joint. 22,23) The fatigue rules in Eurocode 9 accounts for this effect. A further refinement in the IIW recommendations modifies the thickness correction exponent p for various welds.…”