Development of forming limit curves for high strength steels

The aims of this research are experimental to determine forming limit curves (FLC) for high-strength steel sheets (JSC440W) with a thickness of 1.2 mm. and use forming limit curves from experiments to analyze forming sample and compare with FLC from finite element method. In order to create Barlat's yield criteria (Yld 89) equation, which used in DYNAFORM 5.9.4 to predict material behavior, the tensile test and physical test need to be examined, along with the crystallographic structure that can be analyzed by using a microscope. Subsequently, the sheet samples were stretch-formed into a hemispherical dome shape in a hydraulic press and stopped when a local neck or cracks were observed, measuring the dimensions of the grid circles in the necked areas to determine major and minor engineering strains to form a forming limit curve. The results showed that the forming limit curve appropriate with EN ISO 12004-2 standard can be used to apply for analyzing workpiece forming. The experimental FLC show that it can predict failures accurately with the forming sample. Therefore, the forming simulation can efficiently help to improve the quality and production.