Fatigue life assessment of welded joints under variable amplitude loading - state of present knowledge and recommendations for fatigue design regulations
Investigations of cumulative damage were carried out on two types of welded joints (butt welds and transverse stiffeners) of four structural steels, S355M, S690Q and S960Q in the thickness of t = 10 and 25 mm. Further investigations were performed with laser beam welded hollow hat specimens of an automotive steel DC04 and an aluminium alloy AA 5083 with sheet thicknesses of 2 and 3 mm. The random spectra used were of Gaussian type. By applying the Palmgren-Miner rule modified by Haibach most fatigue life estimations with the conventional damage sum D = 1.0 were on the unsafe side. For cumulative fatigue design the evaluation of the results suggest the use of an allowable damage sum of D al = 0.5 with the slope of k = 3 up to the knee point of the SN-curve at 1-107 cycles and k' = 5 after the knee point. This applies for steel as well as for aluminium welded joints.