Material hardening of a high ductility aluminum alloy from a bulge test

Abstract

This study employs the hydraulic bulge test in combination with analysis to extract the stress–strain response of an anisotropic Al-6022-T43 sheet metal. Tests are performed in a facility with a 150 mm aperture and the deformation of the bulge is continuously monitored via 3D digital image correlation. The relatively high ductility of this alloy enabled the bulge to deform well past a pressure maximum, reaching a strain of 0.66 at rupture. After the pressure maximum, deformation localized around the apex and the strain profile acquired an increasingly conical shape. Anisotropy is modeled with Barlat's Yld04-3D yield function, calibrated through a set of independent experiments. The measured strains and curvatures at the apex are used in conjunction with membrane equilibrium and Yld04-3D to extract the material stress–strain response. The procedure adopted does not assume an equibiaxial state of stress or strain. A finite element model of the bulge test that includes the draw bead and clamping hardware is used to simulate the experiments. The model accurately reproduces all aspects of the experiment including the strain profile and its localization after the pressure maximum. A parametric study of the problem revealed that the particular anisotropy of the analyzed sheet did not influence the overall behavior of the bulge, but affects the onset of failure in the presence of MK-type thickness imperfections. The amount of material slipping over the draw bead during pressurization, however, is shown to have a more significant impact on the bulge response and the extracted stress–strain response.