Fatigue strength of welded butt joints in thin and slender specimens

This paper investigates the geometrical properties of the butt-welded thin and slender specimens and their influence on the fatigue strength. The fatigue tests and the finite element analysis are used to investigate the influence. The weld shape, axial misalignment and angular misalignment and the actual shape of the specimen are studied by the extensive optical geometry measurements. The structural hot spot and the notch stress method are used for the fatigue strength assessment. The results reveal that for thin and slender specimens the straightening under the axial loading is significant and thus the relationship between the structural and the nominal stress is highly nonlinear. The straightening effect is influenced by the slenderness and by the curved shape of the plate near the weld. If these effects are included by applying the geometrically nonlinear analysis the fatigue strength of thin and slender welded specimens in notch stresses at two million load cycles corresponds to that of thick welded specimens. The relationship between the structural and the notch stress is however constant regardless of the specimen straightening.