Notched fatigue behavior and stress analysis under multiaxial states of stress

The effect of notches on multiaxial fatigue behavior was studied using thin-walled tubular 2024-T3 aluminum specimens with a circular transverse hole. Constant amplitude fully reversed axial, torsion, and in-phase and 90° out-of-phase axial–torsion tests were performed in load control. Stress analysis was performed using both Neuber’s rule and FEA to study local stress distributions. Neuber’s rule was found to be in reasonable agreement with FEA results for all loading conditions considered. Fatigue crack initiation for all loading cases examined was experimentally observed to occur on planes of maximum shear. For the same equivalent nominal stress, experimental lives in pure torsion were longer than those for pure axial loading. In-phase fatigue lives were also longer than out-of-phase lives at the same equivalent stress. The nominal stress–life approach, applied by considering the fatigue notch factor along with both maximum principal stress and von Mises equivalent (or effective) stress, produced mostly non-conservative fatigue life predictions that varied by as much as a factor of 10 from experimental results. The local stress and strain–life approaches, based on von Mises effective stress or strain, resulted in reasonable correlation of test data at shorter fatigue lives, but became increasingly less accurate in the mid to high cycle fatigue regime, where predictions were in error by more than a factor of 10. The Fatemi–Socie critical plane parameter correlated all test data reasonably well (typically within a factor of 3) and is consistent with the experimentally observed damage mechanism for the tested material.