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The behaviour of a metal sheet when forming can be predicted with accuracy if the forming limit curve is known (FLC). Generating an FLC is a two-step process that involves forming the material blanks and measuring the strain. This can be done by using the Marciniak or Nakazima tests. In this experimental paper, the Nakazima test was used and is conducted using a hemispherical punch, retaining plate, and draw beads, to prevent the blank from slipping, along with the ARAMIS digital image correlation (DIC) system, used for measuring. Metal sheets of magnesium alloy AZ31B were used, with thicknesses of 0.5 mm and 1.0 mm. The settings of the testing equipment have been selected to allow the material to break at different strains: from uniaxial to biaxial stretches. Each specimen represents specific stress in the strain limit diagram. The geometries of the material and its thicknesses have the same leading role in creating tensions. Compared to the tensile compression test, this test confirms better formability of sheets with a thickness of 0.5 mm.