Damage accumulation under variable amplitude loading of welded medium- and high-strength steels

The paper presents the calculation of cumulative damage for two types of welded joints (butt weld and transverse stiffeners) of four steels (medium to high strength): S355N, S355M, S690Q and S960Q. This calculation is based on experimental data obtained under axial loading and bending with constant and variable amplitudes (Gaussian distribution and Gauss with overload spectrum). The experiments were performed under fully reversed (R=−1) and pulsating (R=0) loading. The fatigue life is calculated using the modifications of the Palmgren–Miner–Original rule, according to the Palmgren–Miner–Elementary method, as well as to Haibach’s suggestion. The fatigue life does not depend on the material’s strength. For the investigated welded specimens, mean stresses did not influence the fatigue strength, since high tensile residual stresses already existed. For fatigue life calculations the real damage sum Dreal=0.3 is suggested.