Fatigue behavior of aluminum alloys under biaxial loading

The biaxiality effect, especially the effect of non-singular stress cycling, on the fatigue behavior was studied, employing cruciform specimens of aluminum alloys 1100-H14 and 7075-T651. The specimens, containing a transverse or a 45 degrees inclined center notch, were subjected to in-phase (IP) or 100% out-of-phase (hereinafter referred to as "out-of-phase or OP") loading of stress ratio 0.1 in air. The biaxiality ratio lambda ranged from 0 to 1.5, and 3 levels of stress were applied. It was observed that: (1) at a given lambda a lower longitudinal stress induced a longer fatigue life under IP and OP loading, and the fatigue life was longer under IP loading, (2) the fatigue crack path profile was influenced by lambda, phase angle (0 degrees or 180 degrees), and initial center notch (transverse or 45 degrees inclined); (3) the fatigue crack path profiles, predicted analytically and determined experimentally, had similar features for the specimens with a transverse center notch under IP loading; and (4) the fatigue crack growth rate was lower and the fatigue life longer for a greater lambda under IP loading, whereas it changed little with change in lambda under OP loading. These results demonstrate that non-singular stress cycling affects the biaxial fatigue behavior of aluminum alloys 1100-H14 and 7065-T651 under IP and OP loading. Published by Elsevier Ltd.