Misalignment and tapered transition effects on fatigue of plate joints: analytical solutions and validations

Abstract Misalignments in welded joints are increasingly prevalent in modern shipbuilding due to industry’s shift towards lighter, thinner plates. Greater susceptibility to weld-induced distortions and the need for thickness transitions introduce secondary bending stresses that adversely affect fatigue life. Despite advancements in structural analysis, current industry fatigue design guidelines for treating misaligned joints largely rely on empirical formulations from the 1970s and 1980s. An improved methodology for determining stress concentration factors (SCF) is introduced, with new solutions for pure axial misalignments and misalignments due to transitions in thickness. Analytical solutions are developed using both direct and energy method approaches for a wide range of boundary conditions and geometries. Results are independently validated using the “ASME Boiler and Pressure Vessel Code” mesh-insensitive structural stress method and master SN curve, highlighting substantial shortcomings in widely adopted industry standards. IIW’s SCF formulations contain empirical adjustment terms that lack theoretical justification and general applicability to diverse loading and boundary conditions. This is shown to often result in unconservative stress predictions and an overestimation of fatigue life by as much as seven times for simple geometries consistent with recent Coast Guard builds, compared with analytical solutions and the master SN curve. Additionally, an explicit analysis of tapered transitions in thickness yields a closed-form solution – validated against published data – that shows IIW recommendations overestimate the benefit of tapering by assigning an overly generous fatigue category.