Identification of sheet metal plastic anisotropy using heterogeneous biaxial tensile tests

The plastic behavior of anisotropic steel and aluminum sheets is identified by combining the results of classical uniaxial tensile tests and heterogeneous biaxial tensile tests on non-standard cruciform specimens specifically designed for obtaining a high sensitivity of strain fields to material anisotropy. The strain fields are measured on the surface of the specimens by means of an image correlation method. The 8-parameter anisotropic yield function proposed by Ferron et al. [1] is adopted for identification. On the one hand, the results of uniaxial tensile tests are analyzed to determine the strain-hardening parameters and yield function parameters related to transverse strain-anisotropy (angular variation of the anisotropy coefficient R) and stress-anisotropy (angular variation of the yield stress σ). On the other hand, strain fields measured in the biaxial tests are used as input data in an optimization procedure that consists of fitting simulated fields with experimental ones in order to determine the material parameters describing the shape of the yield surface in the biaxial stretching range. The identified yield function is validated using experimental data issued from biaxial tests that were not considered during the optimization process.