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

• Published in: Acta metallurgica sinica : English letters 2015-12, Vol.28 (12), p.1503-1509
• Main Authors: Ito, Yasuhiro, Nakazawa, Yoshiaki, Kuriyama, Yukihisa, Suzuk, Katsuyuki, Suzuki, Noriyuki
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Circumferences; Corrosion and Coatings; Deformation; Ductility; Expansion forming; Fracture mechanics; High strength steel; High strength steels; Influence; Investigations; Materials Science; Mechanical properties; Metallic Materials; Nanotechnology; Numerical analysis; Organometallic Chemistry; Punches; Spectroscopy/Spectrometry; Steel; Strain; Stresses; Tribology; Variability; 下线; 服务; 迁移
• ISSN: 1006-7191; 2194-1289
• DOI: 10.1007/s40195-015-0350-5

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.