Fatigue failure investigation for different types of aluminum alloy fillet joints by means of the equivalent structural stress method

This study aims to quantify and unify the fatigue life and fatigue strength assessment of four 7N01 aluminum alloy fillet welded joint configurations-lap welded joints (LWJ), T-welded joints (TWJ), non-load-carrying cruciform welded joints (NLCWJ) and load-carrying cruciform welded joints (LCWJ)-by using the equivalent traction structural stress (ETSS) method. Potential fatigue-critical locations and their stress distributions were first evaluated using ETSS. Full-scale fatigue tests were then carried out for all four joint types to obtain comparative fatigue performance. Finite element models were subsequently established to compute ETSS values at the experimentally observed critical failure locations. Finally, the fatigue lives of the different joint geometries were correlated through a master ETSS-N curve to standardize fatigue characterization across configurations. The master ETSS-N framework successfully consolidates fatigue data from joints with markedly different geometries into a unified relationship. The ETSS calculations exhibit insensitivity to mesh density, supporting its robustness for numerical implementation. Across all joint types, the experimentally measured fatigue lives are in strong agreement with ETSS-based predictions, confirming the reliability of ETSS for fatigue assessment of aluminum alloy fillet welded joints. The work provides a geometry-independent and mesh-insensitive fatigue assessment route for 7N01 aluminum fillet welds by establishing a master ETSS-N curve validated by experiments. The proposed approach offers a consistent theoretical and practical basis for fatigue design and life prediction of welded aluminum alloy structures involving diverse fillet-joint configurations.