Numerical and experimental investigation of weld root fatigue in fillet-welded structures

Abstract

For fabrication reasons, a great part of the joints in ship structures are welded with non-penetrating fillet welds. This implies the risk of fatigue failure originating from the weld root under cyclic loading. A fatigue analysis may be performed using the nominal stress approach, which is rather coarse, and the crack propagation approach, which is less practical due to the high computational effort. Alternatives are offered by the effective notch stress approach, which assumes a fictitious radius at the tip of the non-fused root faces and by a newly developed structural stress approach for weld failures. The latter is outlined in the paper and applied to the fillet-welded end of a rectangular hollow section (RHS) and to a doubler plate under out-of-plane loads. These represent typical situations with one-sided welds subjected to local throat bending, where fatigue tests have generally shown weld root failure. From the fatigue lives, a design S-N curve based on the structural weld stress is derived. For further verification, the effective notch stress approach is applied to the RHS-joint showing similar results in relation to the design S-N curve as the structural stress approach.