Cracks are frequently found in complicated residual stress fields. It is therefore necessary to take the influence of stress field into account when calculating stress intensity factors (SIFs). In this study, SIFs for 3-D surface cracks in a flat plate model and a T-butt welded model with different dimensions are evaluated using the superposition method. To implement the superposition method, two codes are utilized, a commercial nonlinear finite element (FE) code that will progress the domain integral method using MSC Marc. The other is an open source research code that will progress the interaction integral method using WARP3D, both solutions will be applied to evaluate the SIFs. The crack face traction term (CFT-term) is neglected for the MSC Marc solution. However, the CFT-term is included in the WARP3D solution to examine the significance of this term on the accuracy of the solutions obtained by crack face traction. The SIFs calculated by direct solution, for a flat plate model and a T-butt welded model, are validated through well-established results. The accuracy of the superposition method is verified by comparing the SIFs obtained by crack face traction with those given by direct solution.

It was found that the difference between the solutions at the deepest point of the crack was less than 5%, even when the CFT-term in the domain integral method was neglected. This shows that commercial nonlinear FE codes that neglect the CFT-term can be applied for engineering problems under the conditions examined in this study. As well, the CFT-term in the interaction integral method showed a significant improvement in the accuracy of the solutions given by crack face traction for a flat plate model. It was found that the difference between the solutions was less than 0.5% at the crack deepest point.