Residual Stresses and Fatigue Behavior of High Strength Structural Steels with Fillet Welded Longitudinal Stiffeners

Abstract

AbstractResidual stresses may affect the behavior of welded steels under fatigue loading. However, for the design of welded structures the level and distribution of residual stresses from welding are often not known so that tensile residual stresses in the order of the yield strength are conservatively assumed. Stress relief annealing is generally suspected to enhance the fatigue strength. The results presented here focus on the influence of residual stresses and thermal stress relief on the fatigue strength of longitudinal stiffeners made of a mild steel S355NL and a high-strength steel S960QL. The initial residual stress conditions were measured using X-ray and neutron diffraction. In order to characterize the influence of residual stresses on the fatigue strength, specimens were tested in the as-welded condition and after a stress-relieving heat treatment. Fatigue testing was conducted under constant amplitude loading with a stress ratio of R = −1 using samples with high and low stress concentration. It was shown that the annealing process influenced not only the welding residual stresses but also the welding distortion. It was found that welding distortion can be increased by thermal stress relief which again affects the fatigue strength.