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The effect of axial misalignment on the fatigue strength of load-canying transverse cruciform welded joints was investigated using experimental and fracture mechanics methods. Where failure occurred by cracking from the weld toe, misalignment significantly reduced the fatigue strength. The reduction could be predicted using a nominal stress concentration factor (SCF). Misalignment had less effect where failure was due to cracking through the weld metal; an expression was deduced for the SCF in this case.For fracture mechanics assessments, an expression for an effective stress intensity factor using the SCF and stress intensity factors for aligned welds was shown to agree with the finite element (FE) results. Predictions of the effect of misalignment using the FE results agreed with experimental data. Misaligned transverse load-carrying cruciform joints should be assessed for fatigue failure from the toe using the same SCF as for a butt weld with the same misalignment. For failure through the throat, an alternative expression for the SCF is recommended. Fracture mechanics assessments of misaligned joints should be carried out using an effective stress intensity factor derived from the SCF and stress intensity factors for aligned joints. These recommendations are now incorporated in British Standard PD 6493: 1991. NOMENCLATURE a = crack length A = constant in crack growth law C = constant in S-N curve e = axial misalignment E = elastic modulus g = root gap in partial penetration joint h = fillet weld leg length K , = mode I stress intensity factor K,, K , = stress concentration factor for toe failure, and for weld metal failure I,, i2 = distances from end points to joint L =distance between end points rn = exponent in S-N curve and crack growth laws M = bending moment induced by misalignment N = cycles to failure P = axial load R = stress ratio (minimum stress/maximum stress) S = stress range in design S-N curve t = plate thickness S,, S, = nominal shear stress in weld metal due to axial load, and bending load w = weld throat thickness x, Yb = dimensionless stress intensity factor for axial loading, and bending loading Y,, = effective dimensionless stress intensity factor for misaligned joint tl = angular misalignment I = parameter oB, u, = axial stress, and bending stress ranges

Finite element analysis using a two‐dimensional modified‐boundary‐layer approach wasused to model the effects of biaxial loading on crack tip stress fields. Loadings wereapplied corresponding to an elastic KI field, non‐singular T‐stress and a biaxial stress.For through‐thickness cracks the T‐stress inherent in the specimen geometry isaugmented by the external biaxial stress. For surface‐notched specimens the biaxialstress acts out of the crack plane. This effect was modelled with generalized plane strainelements. Results were analysed using the Anderson‐Dodds approach for cleavage andthe Beremin model in the ductile regime. Biaxial loading is predicted to have a largeeffect on the toughness of a through‐thickness crack but little effect on a surface crack.Experimental results from a previous series of large‐scale biaxial fracture tests aregenerally consistent with these predictions.

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