Determination of sheet material properties using biaxial bulge tests

Tensile test, conventionally used to determine the flow stress of sheet materials under uniaxial state of stress, is limited to small amount of strain / deformation (due to necking) compared to higher strain/deformation and biaxial state of stress that occur in practical stamping operations. Therefore, in this study, biaxial bulge tests were developed to determine the material properties (flow stress, anisotropy and formability) over a large strain/deformation range. The developed tests were applied to: a) DR210 steel, b) DDS steel, c) AKDQ steel, d) DP600 steel, and e) AL5754-O. The results were validated by comparing FE predictions with experiments in deep drawing of round cups. This study showed that in many, but not all, cases the tensile data, if properly extrapolated, is adequate for use in FE simulation. However, the bulge test is a better indicator of material formability and quality than the tensile test. This is especially true when material properties are not always consistent and vary from batch to batch, as it is the case with most high strength steels.