Interpretation of overload effects under spectrum loading of welded high-strength steel joints

Within the structural durability evaluation of welded structures under spectrum loading, the influence of overloads on the fatigue life due to special events during service must also be considered. For this, butt welds and transverse stiffeners manufactured from the steel grades S355N/M, 6900 and 9600 were submitted to Gaussian spectra without and with superimposed overload spectra. The overloads harmed only the low-strength joints under pulsating bending. In all the other cases investigated, with low-, medium- and high-strength steels under fully reversed and pulsating loadings, a significant decrease of fatigue life was not observed; on the contrary, a significant increase of fatigue life could even be observed. This behaviour is explained by modelling the notch stresses and strains in the weld toes with the appertaining cyclic elastic-plastic material law and considering the local residual stresses. The modelling comprised also the crack propagation behaviour. Not only the fatigue life to crack initiation but also the crack propagation life is increased by the overload spectra.