Mechanism of Deformation Process and Blank Shape of Stretch Flanging Fracture of High-Tensile-Strength Steel

Abstract

In this study, the stretch flanging fracture of a C-S test piece, which has a curved part (C-part) connected to a straight part (S-part) fabricated using high-tensile-strength steel sheet, is investigated. Both experimental and FEM analyses show several strain concentrations on the edge of the flange, and deformations due to such concentrations can be explained by the consecutive occurrence of the braking effect of the stress gradient. The first concentration of strain, which triggers several strain concentrations, is induced by a nonuniform stress. The cause of the nonuniform stress is considered to be the variation in flanging-up angle during the stamping process. To verify this, a C-S test piece with an additional part (obtained by adjusting the edge contours of the curved part) is also investigated. We concluded that pieces having an additional linear and a serrated edge located outside the additional part are optimal for high formability.