Development of a new and simplified procedure for the experimental determination of forming limit curves

This study aims to eliminate the off-centric initiation of localization caused by friction in the Nakazima testing of forming limit curves (FLCs). Our proposed approach uses an ordinary Nakazima testing equipment and standard Nakazima geometries for specimens. The principle is based on a layer of relatively thick, flexible and durable polyurethane disc, whose coherent deformation ensures strain localization at the pole. The main advantages of this approach are the simplicity of the equipment and testing, inexpensiveness, and yet the coverage of the entire strain range relevant to sheet metal forming. The technique is validated by experimental and numerical FLC investigations.