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This paper details a study of the application of notch stress intensity theory to the fatigue failure mode analysis of the transition in load‐carrying cruciform welded joints. The weldment fatigue crack initiation point is difficult to predict precisely because it usually occurs in the vicinity of the weld toe or weld root. To investigate the relationship between fatigue failure location and the geometry of the weldments, we analysed the weld toe and root asymptotic notch stress fields were analysed using the notch stress intensity factors on the basis of the Williams' solution in Linear Elastic Fracture Mechanics (LEFM). Numerous configurations of cruciform joints of various plate thicknesses, transverse plate thickness, weld sizes and incomplete penetration size were used to investigate the location of the fatigue failure. The strain energy density (SED) surrounding the notch tip was introduced to unify the scalar quantity and preclude the inconsistency of the dimensionality of the notch stress intensity factors for various notch opening angles. The results of the investigation showed that the SED approach can be used to determine the transition zone for a variety of joint geometries. The validity of the SED criteria was verified by comparing the experimental results of this study with the complied results for load‐carrying cruciform welded joints reported in literature.

Welding of steel is a technique frequently used in practical engineering applications; however, their mechanical performance is strongly dependent on the physical metallurgical status of the weldments. In the present study, fully reversed, strain-controlled low-cycle fatigue (LCF) tests were conducted on 10CrNi3MoV steel and its undermatched weldments with strain amplitudes varying from Δε = ±0.5 to ±1.2%. Both base metal and weldments exhibited softening behavior at the beginning of the cyclic stage. Numerical investigations of cyclic stress–strain evolutions of the materials have been studied by the cyclic plastic model considering nonlinear hardening. The continuous damage mechanics (CDM) theory based on the experimental hysteresis stress–strain energy concept was employed to illustrate LCF failure, including damage initiation and deterioration. The damage mechanics approach calibrates the material parameters from the measured fatigue life for initiation and growth stages. Afterward, the combination of material cyclic plastic parameters and damage parameters was implemented to predict the LCF life. Good agreement can be observed between the experimental results and the FE results based on the CDM approach. Finally, the damage evolution of the materials under different strain amplitudes by this approach was assessed.

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Pipe reeling may lead to plastic pre‐deformation (prestrain) around existing cracks in components; therefore, investigating whether this process accelerates or counteracts ductile crack growth, especially for strength mismatched welded joints, is warranted. This study focused on the effect of prestrain history on ductile crack growth in mismatched welded joints. A single‐edge‐notched tension specimen was selected for numerical study, and the crack was assumed to have existed before a prestrain history was applied. Crack growth resistance curves for plane strain and mode I crack growth under large‐scale yielding conditions have been computed using the complete Gurson model. Meanwhile, symmetrical and non‐symmetrical prestrain cycle modes with different loading levels were applied to the overmatched specimens. The outcome demonstrated that the mismatch ratio (the ratio between the yield stress of the weld metal and base metal) showed a significant effect on fracture resistance regardless of the stage at which the prestrain cycle loading was located. By contrast, the processing of the crack growth was weakened by the increase of prestrain values, and the symmetrical prestrain cycle resulted in greater plastic damage than the non‐symmetrical prestrain cycle did. However, the initial crack length had a non‐significant effect on the ductile fracture considering the prestrain and mismatch effects.