Study on the Fracture Elongation of the Steel Sheet at the Intermediate Strain Rate

While the formability is important and indispensable for success in very complicated sheet metal forming, it seems that few studies has been carried out about the formability of sheet metal at the high strain rate. The present experimental results report that the elongation is dependent on the crosshead speed in tensile tests. In this paper, the tensile elongation has been obtained from various steel sheets for an auto-body at the intermediate strain rate. The strain rate in the experiment is ranged from 0.003/sec to 200/sec. The experimental result demonstrates that the tensile elongation does not decrease as the strain rate increases. This tendency has varieties depending on the microstructure and forming history of sheet metal. Some high strength steels have the tendency that the tensile elongation increases as the strain rate increases, while o thers not. This phenomenon is very important not only in sheet metal forming but also in the crashworthiness evaluation to predict the fracture and tearing of sheet metal members.