Comparison of nonlinear strain path correction models for the FLD characterization

The Forming Limit Diagram (FLD), along with the Forming Limit Curve (FLC) it encompasses, are widely used tools in sheet metal forming to predict the forming behavior of sheet metal. The experimentally determined FLD depend to some extent on the stretching tests used, like the Nakajima or Marciniak tests. Numerous correction models have been proposed over the last 50 years for the effects of the non-linear strain path, curvature, or normal stress. The purpose of this paper is to summarize and compare the mathematical formulations and properties of existing correction models for the non-linear strain path influence on the Nakajima test results. It appears from the analysis that a large number of the available models share identical hypotheses and results, which simplifies and further guides the user's efforts in selecting the adequate correction model.