A model for modifying the S-N curve considering the effect of boundary conditions on the fatigue crack growth of welded components

The present study proposes a novel model to modify master S-N curves of components according to their load redistribution capability reflected in different boundary conditions (BCs) based on the fracture mechanics analysis. To that end, a comprehensive numerical study was conducted on a Single Edge Notch Bend (SENB) specimen constrained with different kinematic BCs using discrete fatigue crack growth (FCG) simulation. It was observed that BCs indeed can have a significant effect on the crack growth behavior and consequently on the resulting fatigue life under the same nominal loading conditions. The proposed model was applied to the S-N curve of a T-welded joint, and the predicted fatigue life was validated against 3D FCG simulations. Finally, FCG tests were conducted on SENB specimens to experimentally corroborate the effect of BCs on the FCG rate. Boundary conditions significantly affect crack growth, fatigue life, and S-N curve. Increase accuracy of S-N curve predictions by considering boundary condition effects. Proposed model is straight forward to apply through application of a restraint factor. Application of model is shown using fatigue crack growth simulation of T-welded joint.