Effect of weld imperfections on the fatigue resistance of butt-welded connections

Existing standards and recommendations such as prEN 1993-1-9, IIW recommendations, and EN 13001-3-1, provide reference values for the fatigue resistance of butt-welded connections with reference to ISO 5817 quality levels. Nevertheless, these quality level requirements are primarily based on conservative assumptions and limited experimental validation. The present paper investigates the impact of common weld imperfections on the fatigue resistance of one-sided butt-welded connections. A total of 24 specimens was examined, incorporating intentionally imperfections such as undercut, porosity, and excess weld metal. In addition, imperfections including lack of penetration, inclusion, and lack of fusion were assessed based on existing experimental tests. Non-destructive testing using radiography and 3D scanning enabled a detailed classification of imperfections in accordance with ISO 5817. Constant-amplitude axial fatigue tests were performed, and characteristic fatigue resistances were evaluated at two million cycles with a 95% survival probability. The results were compared with previous experimental data and with FAT 71 (fatigue strength), which represents the characteristic fatigue resistance of the analyzed constructional detail. Undercut and lack of fusion at quality levels D or <D reduced fatigue strength by approximately 13% relative to FAT 71, whereas porosity (quality level <D) and excess weld metal (quality level C) caused minor reductions of 3% and 2%, respectively. Despite the presence of these imperfections, the specimens maintained relatively high fatigue resistance, suggesting that the uniform application of quality level B to all fatigue-loaded details may be conservative and a refined evaluation of the influence of weld imperfections is needed.