Multiaxial fatigue evaluation of laserbeam-welded magnesium joints according to IIW-fatigue design recommendations

Under non-proportional multiaxial loading, welded magnesium joints show a decrease of fatigue life compared to combined proportional loading as is also observed for welded ductile steels and aluminium alloys. The investigated laserbeam-welded overlapped tube-tube joints of the wrought magnesium alloys AZ31 and AZ61 were tested under combined in- and out-of-phase axial loading and torsion. The IIW-Recommendations for the evaluation of multiaxial stress states with constant and with changing principal stress directions describe, on the safe side, the results obtained for fully reversed loading R = −1 and the probability of survival Ps = 50 %. The comparisons of the experimental results with the allowable values for Ps = 97.7 % and R = 0.5 are quite conservative. However, as, at present, relatively few multiaxial fatigue investigations with magnesium alloys in the welded state are available, the suggested IIW procedure, the Gough-Pollard Equation with the multiaxial damage parameters DMA = 1.0 and 0.5, should be retained.