EXPERIMENTAL AND NUMERICAL ANALYSIS OF HYDROSTATIC PRESSURE IN DUCTILE FRACTURE OF AL-6061T6

In this paper, a combination of experimental tests and numerical simulations is used to investigate the effects of stress triaxiality and the Lode angle parameter on the ductile fracture behavior of 6061-T6 aluminum alloy. Ductile fracture is a critical failure mode in aluminum components, and its accurate characterization is essential for the safe and reliable design of engineering structures. Instead of performing conventional biaxial tests, uniaxial tensile and compression tests on specifically designed geometries are carried out to generate negative stress triaxiality conditions. To examine the influence of negative stress triaxiality on fracture strain, several specimen geometries are designed to achieve various levels of negative stress triaxiality. The introduction of curvatures and notches alters the local stress state from uniaxial to multiaxial conditions. A standard dog-bone specimen is tested under tension, while specimens M1, M2, M3, M4, and M5 are specifically developed to investigate the effect of different stress triaxialities under uniaxial loading. Since these geometries have not been previously reported in the literature, no standard testing procedure is available for them. Each test is repeated three times, and the average results are reported. Numerical analyses are conducted using the finite element software Abaqus/Explicit to evaluate the behavior of the designed geometries under negative stress triaxiality. To capture ductile damage evolution in the simulations, the built-in ductile damage model in Abaqus is employed. The obtained negative stress triaxiality values range from −0.355 to −0.555, while for the standard dog-bone specimen under tension, the stress triaxiality remains approximately 0.33, representing uniaxial loading. By comparing the results of experimental tests and simulations, a strong agreement is observed, confirming that both approaches predict similar fracture strain values. Based on the damage contours obtained from the numerical analysis, the fracture initiates in regions exhibiting the highest plastic strain, which are consistent with the experimentally observed failure locations. It is further observed that stress triaxiality has a significant influence on ductile fracture behavior, and the trend of fracture strain variation differs between positive and negative triaxiality regimes.