Abstract
Forming limit diagram(FLD) is made to evaluate the forming limit strain of sheet materials. However, even if the macro strains on FLD obtained by scribed circles are same, the micro structures of strained sheet metals are not always same. The fracture limits also depend on micro structures, for example whether uni-elongate order grains or equi-elongate disorder grains. In some case, measured strains depend on scribed circle diameters because of strain gradients in circle. Statistical grain strains can be used to evaluate the strain gradients of strained materials.
