Inverse identification of large strain plasticity using the hydraulic bulge-test and full-field measurements

The hydraulic bulge test (HBT) is an important experimental technique to identify the properties of materials and, in particular, metals. One of the main advantages of such technique, in testing metals, is the possibility of reaching high levels of deformation before fracture. Moreover it allows the investigation of a biaxial loading condition. A hemispherical test can be performed using mechanical punches or the hydraulic pressure of a fluid. When hydraulic pressure is used, the test is not affected by friction. The hydraulic bulge test (HBT) is therefore a very efficient method to evaluate the properties of metals at large strains. Usually, the outcome of the HBT is the hardening curve in the equi-biaxial stress state that occurs at the top of the dome, during the expansion. In this paper a different approach is proposed, where the full-field displacement field obtained with stereo-DIC is used in an inverse identification scheme. The finite strain theory is used to map the stress and strain in the reference configuration so that the problem can be reduced to a 2D plane stress case. The method was first validated using a numerical model of the HBT and then applied on a real test performed on a BH340 steel.