Determination of approximate point load weight functions and fatigue crack growth analysis for U-rib-to-deck joints

Abstract

This study presents the application of the weight function method (WFM) for analyzing fatigue crack growth life (FCGL) in semi-elliptical cracks under complex two-dimensional welding residual stress (WRS) conditions in U-rib-to-deck joints. A novel point load weight function was proposed, accounting for various crack configurations, including weld angle (θ), aspect ratio (a/c), crack depth ratio (a/T), and deck-to-rib thickness ratio (T/t). This new weight function was validated against multiple stress distributions. It was then applied using the NASGRO fatigue crack propagation model to determine stress intensity factors (SIF) and predict the FCGL under varying WRS conditions, initial crack aspect ratios, and cyclic load scenarios. Results indicate that the proposed weight function provides high accuracy for both one- and two-dimensional stress distributions. Tensile WRS significantly increases the SIF at the weld toe, accelerating fatigue crack growth by approximately 60 % compared to cases without WRS. The initial crack aspect ratio (a/c) plays a crucial role in determining FCGL, with higher ratios leading to longer FCGL and slower crack growth, stabilizing at approximately a/c = 0.6 in the later growth stages. Additionally, increasing cyclic stress peak shortens the linear crack growth phase, accelerates propagation, and reduces FCGL, highlighting the importance of mitigating high-stress conditions and WRS in U-rib-to-deck joints to extend their FCGL in practical engineering applications. Overall, the proposed method offers a conservative yet acceptable accuracy in evaluating the FCGL of U-rib-to-deck joints.