Correlation of fatigue life of fillet welded joints based on stress at 1 mm in depth

Fillet welds are widely used to connect attachments, such as gussets or cover plates, to steel structures. The geometric discontinuity caused by the introduction of fillet weld and the attachments leads to stress concentration. Fatigue cracks may form at weld toe at the end or edge of the attachment when the structure is subjected to cyclic loadings. In this study, stress distribution around weld toe region is studied with a non-load-carrying cruciform joint. It is found that the weld toe shape, i.e., weld toe angle and weld toe radius, is crucial in affecting stress concentration at weld toe, but the affecting region is limited with 1 mm in depth. The effect of weld size (leg length) of the weld bead is less significant than that of weld toe shape. The stress at 1 mm in depth in the cross section of the main plate passing weld toe is taken as an indication of geometric effects of the welded joints. If fatigue test results of fillet welded joints are expressed in terms of stress range at 1 mm in depth, which contains effect of geometry of welded joint except that of weld bead, the scatter of test data will only reflect the effect of weld profile. Thus correlation between different types of fillet welds can be established by means of stress at 1 mm in depth. Fatigue test results are collected for non-load-carrying cruciform joints with about 10 mm thick of main plate and attachment. In these joints, the geometric effect of transverse attachment is rather small, and FEM analyses also show their stresses at 1 mm in depth to be around unity. The scatter band of these test data matches well with those of test data of in-plane and out-of-plane gussets plotted in terms of stress range of 1 mm in depth.