Fatigue Behavior of Steel Plates with Inclined Butt-Welded Joints

Spiral welded steel tubes are typical welded steel tubes for offshore engineering piles, which undergo fatigue loading from sea breezes, water fluctuations, and wave impact. Therefore, fatigue failure is one of the main failure modes of these tubes. This paper aims to investigate the fatigue behavior of the local steel plate cut from the spiral welded steel tube. Due to the weld seam in the tube being spiral, the butt-welded seams in the steel plates are inclined by different angles (i.e., 30°, 45°, 60°, 90°) to the loading axis. Initial cracks were artificially induced to the weld toes at either edge of the plates. Thus, fatigue tests were conducted on two types of specimens, that is, type A refers to the specimen whose crack propagated through both the weld metal and the base metal, while type B refers to the specimen whose crack propagated only through the base metal. First, for both type A and type B, the specimens had mixed mode (I + II); in addition, the specimen with a smaller angle yielded a lower fatigue life because it had a longer projection length in the direction perpendicular to the loading axis. Second, the fatigue life of type A specimens was longer than the type B specimens with the same angle due to the influence of the residual compressive stress and the excess weld metal. This paper provides preliminary references for understanding the behavior of such tubes and proposing effective strengthening methods for them in the future.