The Theoretical Prediction of Forming Limit Strains of Sheet Metals in Press-Forming Processes

The theoretical prediction of the forming limit (strain) diagram (FLD), or the forming limit strains of sheet metals by the author's method is reviewed, giving some new and useful information. J2-Gotoh's corner theory; (or MG-) (J2G) constitutive equation previously proposed by the author is used, together with the localized necking condition as the failure condition. Theoretical FLD nets of sheet metals subjected to various proportional loadings are illustrated with the n-value orρ-value as the parameter for the convenience of determining the most appropriate value ofρ(the material constant involved in the J2G). Furthermore, discussions onρ-and n-values and on the material properties of the prestrained sheet are given. The secondary-FLD and the sheet thickness effects on the forming limit strains are also discussed.