Effect of shear angle in shearing on stretch flangeability of ultra-high strength steel sheets

Abstract

Abstract. The effect of the shear angle in shearing on the stretch flangeability of 980 MPa ultra-high strength steel sheets was examined. The sheared edges of the ultra-high strength steel sheets sheared at different shear angles were investigated, and then the cracking on the sheared edge after stretch flanging was observed. The length of the fracture surface in the sheared edge was decreased by shearing with the punch with a shear angle, whereas many cracks and burrs at the edge of the fracture surface were caused, and the boundary between the burnished and fracture surfaces became rougher. In stretch flanging, the cracks in the fracture bottom side rapidly increased with the bending length. The stretch flangeability increased at a shear angle, where the number of cracks per unit length was the highest, i.e. this indicates that the large number of cracks in the sheared edge were effective in suppressing penetration cracking to fracture in the stretch flanging.