Relationship between fatigue performance and weld quality of fillet welds with start-stop positions

Abstract

Surface imperfections may have a strong influence on weld quality and the fatigue life of welded joints. The relation of surface imperfections and fatigue life is given in some cases in weld quality standards like ISO 5817:2023 (Annex B). Currently, surface imperfections are determined according to ISO 17636:2017 by visual testing (VT). The aim of this study is to investigate the application of weld quality assessment by digital visual testing (D-VT) and the relation between weld quality (assessed by D-VT) and fatigue strength for the surface imperfection type “incorrect weld toe” according to ISO 5817:2023 (Annex B). Based on D-VT by 3D-scans, intermittent fillet weld specimens were classified into different quality levels according to ISO 5817 (B, C, D, and < D). Transverse stiffeners were manufactured with different weld geometries. Additionally, some welded specimens contain short surface imperfections (start-stop position), manufactured by interruption of the welding process (intermittent welds). Experimental fatigue test results revealed no significant differences in fatigue life between specimens with and without start-stop positions that are attributed to different quality levels. Although radii of less than 1 mm were observed in all specimens, a fatigue class of at least FAT71 or in most cases FAT80 was determined—contrary to ISO 5817:2023 Annex B, which suggests FAT63 in such cases. The specimens of quality level D are at least related to FAT71. Furthermore, the results reveal that short surface imperfections of the type “incorrect weld toe” that cover less than 10% of the weld length have no significant effect on the fatigue life of welds in the investigated case.