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In this study, a new test method using protruding punch was proposed, that can separate bending and stretch deformations. In this test, the blank contact with the top and shoulder of punch, and the bending angle can be constant. After the bending angle becomes constant, stretch deformation can be applied while the bending deformation remains constant. In addition, this test method can control the inflow of materials by controlling the BHF, and it is possible to evaluate cracks during tensile bending deformation even for materials with low forming limits.
In this test, the obtained forming limit strain was higher than that of FLC during uniform deformation in the thickness direction. It is suggested that this is because the strain gradient in the thickness direction delayed the necking occurrence timing. There is a linear relationship between the strain gradient in the thickness direction and the maximum principal strain on the plate surface, which can be applied to the prediction of tensile bending cracks in FEM analysis.