The through-thickness distribution of welding residual stress in a 30-mm-thick butt-welded Q345qD steel plate has been investigated through experimental measurements and finite-element simulations. In this paper, the weight function and finite element methods are used to investigate the stress intensity factors (SIFs) at the surface and deepest points of the semi-elliptical surface cracks, subjected to a combination of external tensile load and through-thickness welding residual stress. Different crack aspect ratios and relative depths are analyzed. The results reveal that the longitudinal residual stress is always tensile through the plate thickness, which makes the SIFs of the surface and deepest points larger than those without considering the longitudinal residual stress. However, the transverse residual stress through the thickness presents tension–compression–tension, with the tensile transverse residual stress causing the SIFs to increase. When the crack tip enters the compressive stress region, the compressive stress offsets the external load and causes the SIFs to decrease.

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