Fracture Initiation in Aluminum Alloys Under Multiaxial Loading at Various Low Strain Rates

The initiation of ductile fracture in medium-strength AW5754 and high-strength AW6082 aluminum alloys at different quasi-static strain rates and under multiaxial stress states is investigated through a series of tensile tests using various specimen geometries. The sensitivity of the stress triaxiality locus to variations in loading rate is examined for these two aluminum alloy families. Numerical simulations based on the finite element method (FEM) are performed using ABAQUS/Standard to determine the actual stress triaxialities and equivalent plastic strains at fracture. The numerical approach is validated by comparing the simulation results with experimental findings. These simulations facilitate the generation of a stress triaxiality locus through a curve-fitting process. An exponential fitting function is employed to accurately relate the equivalent plastic strain at fracture to the corresponding stress state across different strain rates. The results reveal different strain-rate dependencies for the two alloys within a very low strain rate range. The resulting stress triaxiality loci provide a valuable tool for predicting fracture strains and for more accurately evaluating stress states. Overall, the findings of this study significantly advance the understanding of the fracture initiation behavior of aluminum alloys under multiaxial loading conditions and their sensitivity to various quasi-static loading rates.