Fatigue crack initiation and growth in A517 submerged arc welds under variable amplitude loading

A comparison between fatigue crack initiation and growth predictions for a submerged arc welded butt joint in ASTM A517 steel and the corresponding laboratory results are presented. The fatigue tests of the butt-welded joint involved a variable amplitude spectrum consisting of three storm sequences per year. Fatigue crack initiation, coalescence and growth were monitored using a localised potential drop system. Multiple fatigue crack initiation sites were found along the weld toe of the specimen, and this was followed by fatigue crack coalescence. Fatigue life, crack initiation and growth predictions were carried out using S–N, local notch strain and fatigue crack propagation approaches respectively. A comparison between the predicted and experimental fatigue lives indicated that the S–N and fatigue crack propagation approaches were conservative while the strain life predictions were un-conservative.