Modelling of 3D Fatigue Crack Growth in Tubular Joints: An Automated Framework for CFRP‐Strengthened T‐Joints Under Out‐of‐Plane Bending

This study presents an automated computational framework for simulating three‐dimensional (3D) fatigue crack growth and adhesive delamination in carbon fiber‐reinforced polymer (CFRP)‐strengthened steel tubular T‐joints. The model integrates continuum damage mechanics with the extended finite element method (CDM‐XFEM) to concurrently simulate progressive damage in the steel substrate and failure at the bonded interfaces. A Python‐driven interface automates the cycle‐by‐cycle simulation of crack propagation, material degradation, and selective element deactivation in a finite element programme. Validation is performed using results from high‐cycle out‐of‐plane bending (OPB) fatigue tests. Furthermore, fracture surface morphologies predicted by the model are compared with experimental data acquired from noncontact 3D laser scanning of the tested specimens. The results demonstrate that the framework provides accurate predictions for fatigue life, crack trajectories, debonding zones, and crack growth rates, with deviations of less than 6% in fatigue life and under 1.4 mm in fracture surface geometry.