Hydraulic bulge forming simulation of 6000 series aluminum alloy sheets using anisotropic yield functions and experimental validation

Abstract

Biaxial tensile tests of 6000 series aluminum alloy sheets with different density cube textures were carried out using cruciform specimens. The specimens were loaded under linear stress paths in a servo-controlled biaxial tensile testing machine. Plastic orthotropy remained coaxial with the principal stresses throughout every experiment. Successive contours of plastic work in stress space and the directions of plastic strain rates were precisely measured and compared with those calculated using selected yield functions: the von Mises, Hill's quadratic and Yld2000-2d [Barlat, F. et al., Int. J. Plasticity, 19 (2003), 1297–1319]. The Yld2000-2d yield functions with exponents of 12 and 6 are capable of reproducing the general trends of the work contours and the directions of plastic strain rates observed for test materials with high and low cube textures, respectively. Hydraulic bulge tests were also conducted and the variations of the thickness strain along the meridian directions of the bulged samples were compared with that calculated using finite element analysis (FEA) based on the Yld2000-2d yield functions with exponents of 12 and 6. The differences of cube texture density cause significant differences in the strain distributions of the bulged specimens, and the FEA results calculated using the Yld2000-2d yield functions show good agreement with the measurement results.