On the use of elliptical bulge tests in material characterization through inverse methodologies

The hydraulic bulge test is an experimental technique that can be used to identify the properties of sheet metals up to large strain. The hydraulic bulge test, usually, is a free expansion of a sheet blank through a circular hole, driven by the pressure of a fluid, where the ends of the blank are blocked using a suitable die. The state of stress during the bulge test is mainly equi-biaxial, however, using elliptical holes with different aspect ratios, it is possible to produce heterogeneous stress-strain fields that can be used to identify the properties of the material through an inverse method; in this case, the non-linear Virtual Fields Method (VFM) was adopted. With respect to the traditional tests employed with the VFM in plasticity, i.e. double notched specimens or specimens with holes subjected to tensile tension, elliptical bulge tests allow to investigate a different zone in the stress-strain space, with a higher triaxiality. The capability of this type of test to calibrate the parameters of advanced anisotropic models is here assessed using simulated experiments.