HFJOINT: A high-fidelity numerical modeling tool for stress concentration factor analysis of welded tubular joints

Abstract

Assessing the fatigue performance of welded tubular joints is crucial to the safety and durability of their host structures. Fast-computing beam-element models are insufficient to accurately capture local stress concentrations at the intersection region, leading to inaccurate lifetime predictions. In this work, a high-fidelity numerical modeling tool, HFJOINT, is developed for stress concentration analysis of welded tubular joints, following a user-friendly process. The workflow begins with the creation of an elementary T/Y-joint using quadratic hexahedron elements, where the weld geometry is generated in accordance with the American Welding Society (AWS) standard. The chord and brace are divided into several regions allowing for an entirely structured mesh. The geometric transformations of multiple elementary joints enable creating more complex joints. After evaluating the stiffness matrix, the beam-element forces are converted to external tractions, and are transformed into solid-element nodal forces via Gaussian integral. The boundary conditions are defined from the geometric constraints formulated by the Lagrange’s equation of the second kind. Based on the nodal displacements, the postprocessing module evaluates the local stress at any point. Using linear extrapolation, the hot-spot structural stress and the stress concentration factors (SCFs) along the weld circumference are computed. The workflow has a computational complexity of $O\left(N^{1.89}\right)$. The mesh convergence shows that the relative changes are below 2% when refining the weld circumference from 64 to 96 segments. The tool is verified against the SCFs of benchmark T-, K- and X- joint models, showing its potential for fatigue analysis of welded tubular joints in broad applications.