The determination of material parameters from superplastic free-bulging tests at constant pressure

Superplastic forming (SPF) of sheets is a very interesting and useful process when there is a need to produce items with complex geometry and integrated structures characterized by high specific resistance. To accurately model SPF processes it is important to know the constitutive equation of the material. With the help of the finite element method (FEM) this study proposes an innovative method for determining the characteristic parameters of superplastic materials. This method requires the material to undergo free-forming tests in which the stress state induced is biaxial (nearer the real stress conditions to which the material is subject during the SPF processes that are of interest to industry). The dimensions of the sheet and the forming die do not place any constraint on the application of this type of characterization procedure. The method adopted to characterize superplastic materials was validated by means of experimental activity carried out on an AZ31 magnesium-based alloy.