Investigation of the effect of loading angle on mixed-mode fatigue crack propagation of AA2024-T351 friction stir welded joint

The present study investigated the fatigue crack propagation behavior of Compact Tension-Shear (CTS) samples made of aluminum alloy AA2024-T351 under mixed mode I + II loading. Two groups of base metal CTS samples and CTS samples with Friction Stir Welding (FSW) joint were used for this purpose. ABAQUS commercial software was used based on the use of Extended Finite Element Method (XFEM) and Virtual Crack Closure Technique (VCCT) to implement static and fatigue analyses, and the results of the research were compared with the experimental results. Based on the obtained results, it was found that the use of the finite element approach with the simultaneous use of XFEM and VCCT techniques and the division of the welding cross-section into areas with different mechanical and fatigue properties leads to a proper estimation of the fatigue crack growth path and the fatigue life. The numerical results from the fatigue tests agreed with those from the experimental work. Regardless of the load application pattern and loading angle, the equivalent stress intensity factor in the weld crown was more significant than the weld bottom area for all CTS samples with FSW joint. On average, the weld bottom area suffered a 17% increase in the equivalent stress intensity factor compared to the weld crown area. For both categories (base metal samples and FSW joint samples) in loading conditions in the dominant mode II, with loading angles of 0 and 30 degrees, the fatigue life was much higher than in the conditions of dominant mode I, with loading angles of 60 and 90 degrees. In base metal CTS samples and FSW joint CTS samples, fatigue life decreased by 59% and 84%, respectively, by increasing the loading angle from 0 to 90 degrees.