Effects of overload mode-mixity on fatigue damage behavior and governing micromechanisms in AA7075 under biaxial fatigue loading

An investigation into the effects of overload mode-mixity on crack growth behavior and governing micromechanisms of AA7075 T6 has been conducted. Cruciform AA7075 T6 specimens were subjected to constant amplitude planar biaxial fatigue with single overloads, and key fatigue damage behavior, including fatigue life, crack growth rate, and recovery distance, were investigated and correlated to overload parameters. Additionally, SEM fractography was conducted to identify and relate fracture surface features to governing fatigue damage micromechanisms. An increase in fatigue life was observed for all cases of mode-mixity, with the minimum increase occurring at 45°. The mix-mode overloads also caused crack retardation in all cases. In the shear dominant overloads, however, initial post-overload crack acceleration occurred and was immediately followed by crack retardation. Microscale analysis showed distinct fracture features in the pre-overload, transient, and post-overload regions for both tensile and shear dominant overloads.