Ductile fracture of 2024-T4 aluminum alloy: the roles of stress triaxiality and Lode angle

The ductile fracture behavior of metals is profoundly influenced by the stress state, often determined by stress triaxiality and the Lode angle, as well as the strain rate. This study delves into the ductile fracture mechanisms of 2024-T4 aluminum alloy under multiple stress states, including pure tensile, pure torsion, and a combined tensile-torsion scenario. We employ a state-of-the-art electromagnetic tensile-torsion split Hopkinson bar for dynamic testing and a servo-hydraulic testing machine for quasi-static testing. By utilizing two high-speed cameras and three-dimensional digital image correlation techniques, the fracture properties and strain distribution of the specimens were accurately captured. The test results demonstrated that the fracture properties of specimens are significantly influenced by the stress state, while they are not sensitive to the strain rate within the tested range. In light of the experimental data, the Johnson-Cook (J-C) model and the ASCE-modified J-C model are calibrated and compared. The ASCE-modified J-C model shows improved accuracy with the introduction of the Lode angle parameter. Furthermore, the micro-fracture mechanisms under different loading conditions that occur in the evaluated specimens are studied.