The accurate evaluation of structural integrity necessitates considering the influence of crack-tip constraints and selecting laboratory test specimens that accurately represent the actual welded structure. In this paper, a constraint parameter Dp covering in-plane constraint and out-of-plane constraint is defined based on the equivalent plastic strain gradient at the adjacent zone of the crack front. The USDFLD (user-defined field) subroutine is employed to correlate the mechanical property parameters of the continuous transition with the geometry of the dissimilar metal-welded joint (DMWJ). The submodel technique is used to study the crack-tip constraint of a typical DMWJ under complex loading conditions. The crack-tip constraints of DMWJs are quantitatively characterized. A comparison and analysis are carried out to determine the suitable test specimens for the DMWJs with various crack lengths and locations.

The results show that the cracks located at the center of the specimens are more likely to propagate than surface cracks. The interface of SA508/52Mb is the most dangerous position in DMWJs. The constraint levels of SA508/52Mb cracks match those of the center-cracked tension [CC(T)] specimens with smaller width and thickness. Overly conservative estimation results will be produced if compact tension [C(T)] and single-edge notched bend [SEN(B)] specimens with larger width and thickness are adopted to evaluate the stress corrosion cracking behavior of SA508/52Mb cracks.

The constraint levels of 52Mb/52Mw cracks match those of the CC(T) and SEN(B) specimens with smaller width and thickness. The 52Mw/316L cracks match the C(T) specimens with larger width and thickness. Nonconservative results will be produced when the CC(T) and SEN(B) specimens are adopted to evaluate 52Mw/316L cracks.

This study provides a more accurate method for the structural integrity assessment of DMWJs that can help improve the safety and reliability of critical engineering welded structures such as nuclear power plants.