The influence of material model on the neck development for aluminium alloy sheet

The neck development for bore expansion problem is analyzed. Static implicit calculations are carried out for the A2219 Aluminium alloy sheet using ABAQUS/Standard. The equations to give the conditions of the onset of the localized necking of sheet metal based on the general bifurcation theory are presented for plane stress. Since accurate calculation of stresses and strains are the basis for the necking prediction, both associated and non-associated flow rule are adopted in the material model in which Hill's quadratic functions are used. User defined subroutine UMAT is developed using a fully implicit integration scheme. The results of necking prediction show that necking occurrence delays for the Hill solid using both AFR and NAFR based model compared with Mises solid and necking occurrence slightly delays for the Hill solid using AFR based model compared with Hill solid using NAFR based model. Initial necking occurs when equivalent plastic strain is respectively 0.33, 0.39 and 0.348 for the Mises solid and Hill solids using AFR and NAFR based models. Theses indicate that the material model has significant influence on the accuracy of necking prediction.