Effects of Vertical Angle of Conical Punch on Stretch Flangeability of High Strength Steel

作     者：Yasuhiro Ito Yoshiaki Nakazawa Yukihisa Kuriyama Katsuyuki Suzuk Noriyuki Suzuki 

作者机构：Nippon Steel and Sumitomo Metal Corporation The University of Tokyo 

出 版 物：《Acta Metallurgica Sinica(English Letters)》 (金属学报（英文版）)

年 卷 期：2015年第28卷第12期

页      面：1503-1509页

核心收录：

学科分类：08[工学] 0806[工学-冶金工程] 0802[工学-机械工程] 080201[工学-机械制造及其自动化] 

主　　题：Formability Ductile fracture Finite element analysis Hole expansion test 

摘      要：To clarify the effects of the vertical angle of a conical punch on stretch flangeability, hole expansion forming tests were conducted. Test results showed that the hole expansion ratio becomes larger as the vertical angle decreases.Results also showed that the fracture strain at the fracture location on the hole edge was constant and independent of the vertical angle. This is because the hole expansion ratio was controlled not only by the fracture strain, which is independent of the vertical angle, but also by deformation uniformity along the hole edge. From the result of numerical analyses, it was determined that deformation uniformity depends on the gradient of circumferential stress along the radius direction. When the vertical angle is sharp, the circumferential stress showed a steep decline and the deformation localization was suppressed. Consequently, the hole edge deformed more uniformly and the hole expansion ratio became larger. It is concluded that in order to improve stretch flangeability of high strength steel, it is important to uniformly deform the hole edge by applying a conical punch with a sharp vertical angle.