W-shaped bending test
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The minimum bend radius (MBR/t) is the radius below which a test piece can be bent without a crack at the outer surface of the curve. The smaller the value of MBR/t is, the better the bend formability of the material is.
Ex: When the thickness is 0.2mm and the bend radius is 0.2mm, the value of R/t equals 1.0.