Dissimilar metal welded joints (DMWJs) possess significant localized mechanical heterogeneity. Using finite element software ABAQUS with the User-defined Material (UMAT) subroutine, this study proposed a constitutive equation that may be used to express the heterogeneous mechanical properties of the heat-affected and fusion zones at the interfaces in DMWJs. By eliminating sudden stress changes at the material interfaces, the proposed approach provides a more realistic and accurate characterization of the mechanical heterogeneity in the local regions of DMWJs than existing methods. As such, the proposed approach enables the structural integrity of DMWJs to be analyzed in greater detail.

Due to the particularity of welding processes, the mechanical properties of welded joint materials, especially the yield strength, are unevenly distributed, and there are also a large number of micro cracks, which seriously affects the safety performance of welded joints. In this study, to analyze the effect of the uneven distribution of yield strength on the crack propagation path of welded joints, other mechanical properties and residual stresses of welded joints are ignored. In the ABAQUS 6.14 finite element software, the user-defined field (USDFLD) subroutine is used to define the unevenly distributed yield strength, and extended finite element (XFEM) is used to simulate crack propagation. In addition, the static crack finite element model of the welded joint model is established according to the crack propagation path, which is given the static crack model constant stress intensity factor load, and the influence of an uneven yield strength distribution on mechanical field is analyzed. The results show that the crack length of welded joints as well as the plastic deformation range of the crack tip in high stress areas can be reduced with the increase of yield strength along the crack propagation direction. Moreover, the crack deflects to the low yield strength side. This study provides an analytical reference for the crack path prediction of welded joints.

Surface cracks are one of common forms of flaws in thin‐walled structures such as pressure vessels, oil, and gas pipelines. Accurate evaluation of the growth driving force of such surface cracks is important for integrity analyses of these structures. In this study, the combined effect of the depth and the length of a given surface crack under tension was analyzed using combined elastoplastic finite element analysis (EPFEA) and crack propagation experiments with selected crack shapes. Based on the consideration of the distribution profile of the J integral as the crack growth driving force along crack front, the crack growth stability with different crack shapes was analyzed. Finite element analysis (FEA) results showed that the growth from partial to through‐wall penetration is affected by the shape of the initial crack. As shown by the distribution profile of the J integral along the crack front, the location(s) of the maximum J, that is, the highest crack driving force, is (are) found to vary with the crack shape and development.

The crack tip strain and stress condition are one of the main factors affecting stress corrosion cracking (SCC) behaviors in the dissimilar metal welded joint of the primary circuit in the pressurized water reactor. The mechanical property mismatch of base metal and weld metal can significantly affect the stress and strain condition around the crack tip. To understand the effect of different weld metals on strain and stress fields at SCC crack tips, the effects of strength mismatch, work hardening mismatch, and their synergy on the strain and stress field of SCC in the bi-material interface, including plastic zone, stress state, and corresponding J-integral, are investigated in small-scale yielding using the finite element method. The results show a significant effect of the strength mismatch and work hardening mismatch on the plastic zone and stress state in the weld metal and a negligible effect in the base metal. J-integral decreases with the single increase in either strength mismatch or work hardening mismatch. Either the increase in strength mismatch or work hardening mismatch will inhibit the other’s effect on the J-integral, and a synthetic mismatch factor can express this synergistic effect.

Corner cracks are one of the common forms of flaws in the reactor pressure vessels (RPVs) of nuclear power plants (NPPs). Accurate evaluation of the driving force of such corner cracks is essential and critical for the efficient design and integrity assessment of the RPVs. In this study, the combined effect of the depth, length and angle of a given corner crack under the service loading was analyzed using elastic–plastic finite element analysis (EPFEA). Based on the consideration of the distribution profiles of stress intensity factor (SIF) and J integral as the crack growth along corner crack front, the crack growth stability with various crack shapes and angles was analyzed. Finite element analysis (FEA) results showed that the crack growth driving force is affected by the shape and angle of the initial crack. It is also found that the sliding mode (mode II) crack or tearing mode (mode III) crack should be taken into account in the structural integrity analysis of RPVs.