Determination of Forming Limit Stress Diagrams for the Characterization of Material for Sheet Metal Forming

Forming limit diagrams (FLD) are usually used to predict the possible failure of the material in a sheet metal forming process. The FLD shows the maximum strain to failure as a function of the strain state. Another way of describing the deformation limit of a material is a forming limit stress diagram (FLSD), which shows the equivalent stress to failure as a function of the principal stresses. The FLSD is independent of the deformation history and the deformation path of the material, which is in contrast to the commonly used forming limit diagram (FLD). FLSDs for five different deep drawing steel grades have been calculated from data of previously determined FLDs, flow curves, and anisotropy coefficients.