Inverse Identification of the YLD2000-2D Yield Locus Exponent for Stainless Steel 1.4301 Using a Time-Dependent Optimization Method

The non-quadratic yield locus YLD2000-2D is widely used in sheet metal forming to describe anisotropy. In this yield function, the exponent, often denoted by \(m\) , is a material parameter that determines the yield locus shape and is typically defined by the grain structure ( \(m=6\) for body-centered cubic (bcc) and \(m=8\) for face-centered cubic (fcc)). However, recent studies have shown that this assumption is not always the best choice for reproducing the strain distribution of standard experiments, such as the Nakazima tests. In the present work, an inverse time-dependent optimization is proposed to determine the parameter \(m\) for the metastable austenitic stainless steel 1.4301. The material is subject to the Transformation Induced Plasticity (TRIP) effect, and the microstructure transforms from austenite (fcc) to martensite (bcc) during cold forming. The strain distributions along cross-sections of different Nakazima experiments are evaluated at different drawing depths for the inverse optimization. The FE simulation results are compared with the experimental cross-section data in order to determine the optimal values of \(m\) . The outcome is analyzed to quantify the influence of the Nakazima specimen and the drawing depth. Despite the increase in martensite content in the material, the overall optimal value of \(m\) for the stainless steel 1.4301 was determined to be \(m=8\) .