Plastic deformation and ductile fracture of 2024-T351 aluminum under various loading conditions

The plastic deformation and ductile fracture behavior of 12.7 mm thick 2024-T351 aluminum plate is investigated. Tension, compression and shear experiments are conducted at strain rates ranging from 10 -4 s-1 to 5000 s-1 and temperatures ranging from -50 °C to 450 °C. Anisotropy in the plate is studied by conducting tension and compression tests on specimens oriented in multiple directions within the plate. An anisotropic plasticity model is used in numerical simulations of select experiments. Comparison of the simulation results to the actual test data shows that the material behavior can be adequately captured in tension, compression and shear. Anisotropic plastic deformation behavior in an impacted target panel is also investigated. Numerical simulations using both a von Mises and anisotropic yield functions are compared to previously published experimental data. The choice of yield function has a dramatic effect on the predicted projectile residual velocities. Experimental impact data shows evidence of anisotropic behavior, the trends of which can be captured in simulations using the anisotropic yield function. The dependence of equivalent plastic fracture strain on the state of stress is studied through mechanical experiments on specimens with various geometries, subjected to multiple load conditions. Tension tests of plane stress (thin) specimens, axisymmetric specimens and plane strain (thick) specimens are conducted for this purpose. Combined tension -- torsion, pure shear and compression -- torsion tests as well as dynamic punch experiments are also used. The three dimensional digital image correlation (DIC) technique is used to determine the specimen surface strains in many of the experiments. A coupled experimental -- numerical approach is used to generate fracture locus data points for the tension and punch experiments. The equivalent fracture strain dependence on three stress state parameters: stress triaxiality, Lode parameter and product triaxiality is determined. The stress triaxiality parameter alone is insufficient to describe the equivalent plastic fracture strain for all of the stress states examined. A fracture locus in the triaxiality -- Lode parameter stress space is presented.