A presentation given by M. Huang, ArcelorMittal Global R&D, and J.R. Li, Oakland University at the 2019 Great Designs in Steel.
Three failures can be found on drawn parts in the stamping productions. One is the necking and split on the walls of the drawn part that can be predicted with the Forming Limit Diagram (FLD), another one is the necking at the tangent point of a drawn part radius that is controlled by the material n value. These two failures are all caused by the material plastic instability. The third one is the fractures of advanced high-strength steel (AHSS) on part radii when the materials are subjected to an excessive bending under tension load. The failure criterion has yet to be developed to control the issues in stamping productions. In the current study, the fracture limits of four grades of AHSS, i.e. DP590, DP780, DP980 and DP1180, were studied with a simulative 90 degree stretch bending tests and various tool radii (from 1.0mm to 14.0mm). The DIC equipment was used to measure the surface strains and determine the fracture limits. On the basis of test results, the failure criterion has been developed for the four AHSS grades in terms of the permissible tensile strains of materials when they are on different tooling radii (R/t).