Fatigue Assessment of Welded Joints Subjected to Multiaxial Loading Conditions through the Effective Critical Plane Approach

ABSTRACT Reliable fatigue design of welded components under multiaxial loading demands local criteria able to capture both the stress gradient at the weld notches and the influence of a complex loading condition including non proportionality of the stress‐strain load history. The Effective Critical Plane (ECP) approach, based on a stress averaging over a small volume centered at the notch and preserving the full tensor description of the stress‐strain field, meets these requirements. The present work shows that the representative material volume, identified by the control radius , depends on whether it is determined with base‐metal or weld‐metal fatigue data. Using annealed welded‐notched and base metal‐notched specimens two radii are obtained and combined with the Effective Fatemi–Socie and Smith–Watson–Topper critical plane parameters. Fatigue life predictions for S355JR tube‐to‐plate joints subjected to uniaxial, multiaxial proportional, and multiaxial nonproportional loading are then obtained using these parameters. The calibration with weld‐metal properties reduces by nearly half and lowers the scatter of ECP predictions, especially for out‐of‐phase loading, indicating that the weld microstructure governs the relevant length scale in the process zone, where fatigue cracks originate.