Anisotropy and formability of AA5182-0 aluminium alloy sheets

This paper presents a new yield criterion for orthotropic sheet metals and its implementation in a theoretical model of the forming limit diagrams. The equivalent stress equation shows that the shape of the yield surface is defined by eight material parameters. The minimisation of an error-function has been used for the numerical identification of these coefficients. The parameters are established in such a way that the constitutive equation associated to the yield surface reproduces the plastic behaviour of the actual material. The uniaxial yield stresses (sigma(0), sigma(45), sigma(90)), biaxial yield stress (sigma(b)), uniaxial anisotropy coefficients (r(0), r(45), r(90)) have been used in identification. The new yield criterion has been implemented in the Marciniak-Kuczynski theory in order to predict the limit strains. The theoretical forming limit curves have been compared with the experimental ones. The friction free tests, the hydraulic bulge test (for the positive minor strains) and the tensile test for plane strain and for uniaxial tensile test (for the negative minor strains) are used. The predicted yield surface and forming limit diagrams for AA5182-0 aluminium alloy sheets are in good agreement with the experimental ones.