FUJIMOTO Hitoshi Kyoto University, Graduate School of Energy Science, Assistant, エネルギー科学研究科, 助手 (40229050)
HATTA Natsuo Kyoto University, Graduate School of Energy Science, Professor, エネルギー科学研究科, 教授 (30026041)
|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1998 : ¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1997 : ¥1,100,000 (Direct Cost : ¥1,100,000)
In recent years, due to the demand for higher functions in material, such as high strength and high corrosion-resistivity, many steel sheets with special qualities have been developed and increasingly employed in various industries. However, some special steel sheets are much inferior to ordinary steel sheets in formability. In order to find the forming method and conditions suitable for the special steel sheets, the forming limit., i.e. the fracture initiation in sheet forming processes has to be correctly predicted.
In sheet metal forming, the forming limit is generally determined by the onset of localized necking and predicted by the analyses of tensile instability' or bifurcation phenomena. However, the plastic properties of the special steel sheets are not so simple as those of the ordinary steel sheets. In our recent studies, another approach has been proposed. The forming limit, i.e. the fracture initiation is predicted not by the onset of localized necking, but by the occurrence of fracture itself. A criterion for ductile fracture is introduced in the finite element simulation.
In this study, first, the formability of some special steel sheets has been experimentally investigated. Next, the recently proposed approach has been applied to the prediction of forming limit of special steel sheets. The comparison with the experimental results has shown that the forming limits for various sheets are successfully obtained by the present approach, even in no appearance of localized necking. Furthermore, the formability of the laminates composed of steel and aluminium alloy sheets has been investigated.