Limiting strains of sheet metals obtained by pneumatic stretching at elevated temperatures

As uniaxial tensile testing fails to represent the actual loading case in sheet metal forming, evaluation of limiting strains is largely based on forming limit diagrams (FLDs) produced by the Marciniak and Nakazima methods. The accuracy of these methods is subject to uncertainties of the actual deformation state and friction conditions. In addition, they are impractical for studying formability at elevated temperatures, which is of prime importance in forming lightweight alloys. This work presents a detailed systematic methodology for assessing formability and limiting strains by pneumatic sheet metal stretching. The proposed approach is demonstratively applied to the AZ31 magnesium alloy at various conditions.