Multiaxial fatigue behavior and life prediction of 2198-T8 Al-Li alloy notched tubular specimen based on DIC technique

2198-T8 aluminum-lithium alloy is an advanced aeronautical engineering material. The multiaxial fatigue tests of notched specimens are conducted with the variables of notch diameter, notch number, and equivalent stress amplitude, respectively. The strain field and fatigue life are characterized and calculated by digital image correlation (DIC) technique. The results show that: the fatigue life decreases with the increase of notch diameter, number of notches, and the equivalent stress amplitude. The strain curves calculated by VIC-3D are similar to those obtained by the testing. The normal and shear strain concentration becomes obvious at 80% to 90% fatigue life, and the surface cracks appear at 95% fatigue life, typical multiaxial fatigue morphologies including tire patterns and wear fatigue striations are observed on the fracture surface. The feasibility of the DIC technique to characterize multiaxial fatigue behavior is verified. The modified SWT model provides fine life prediction results with all predicted data within a factor of two.