Nominal and local stress quantities to design aluminium-to-steel thin welded joints against fatigue

Welding aluminium to steel to make mechanical joints is possible, but there is, to date, no accepted method for performing the fatigue assessment of such hybrid connections. In this context, the present investigation aims at checking the accuracy of nominal stresses, effective notch stresses, notch-stress intensity factors, and the Modified Wöhler Curve method (applied in conjunction with the Theory of Critical Distances) in estimating fatigue lifetime of butt, cruciform, lap and tee aluminium-to-steel thin welded joints. EWM coldArc® welding technology was used to manufacture the welded specimens that were used for this validation exercise. The samples being tested in the structural laboratory of the University of Sheffield, UK, were manufactured by using AA1050 aluminium and EN10130:1991 steel with main plates thicknesses of 1 mm or 2 mm. The results from this experimental/theoretical investigation demonstrate that all the design methodologies being investigated can be used to perform the fatigue assessment of aluminium-to-steel thin welded joints provided that suitable reference/calibration fatigue curves are used. In the present paper, some quantitative recommendations are given for use in situations of practical interest of the design techniques being considered.