Mechanism of Fatigue Failure Anisotropy of Extruded Al‐Cu‐Li Alloy

ABSTRACT This study systematically investigates the anisotropic failure behavior of extruded Al‐Cu‐Li alloys under very high cycle fatigue (VHCF) conditions. Ultrasonic fatigue testing reveals that, after aging, specimens loaded along the extrusion direction (ED) exhibit significantly longer fatigue lifetimes than those along the transverse direction (TD) and normal direction (ND), with all orientations achieving VHCF performance. A detailed analysis of < 100 > and < 111 > fiber textures demonstrates their pronounced influence on fatigue crack initiation sites, propagation paths, and fracture modes. Finite element analysis and microstructural characterization are combined to establish a mechanism chain linking texture evolution, slip behavior, stress localization, and fatigue crack growth. The results show that the < 111 > texture promotes orientation‐dependent slip constraint and stress accumulation at grain boundaries and unfavorably oriented slip systems, thereby governing the formation of anisotropic fatigue failure modes. These findings provide key mechanistic insight into the fatigue failure behavior of Al‐Cu‐Li alloys and lay a theoretical foundation for their reliable structural application.