The forming limit diagram of ferritic stainless steel sheets: Experiments and modeling

The forming limit diagrams (FLDs) of two ferritic stainless steel sheets of thicknesses 1 and 0.1 mm were determined experimentally. For the 0.1 mm thick sheet, the modified Marciniak test and the conventional ASTM standard test were used for the FLD determination. However, the latter produced wrinkles and buckles on the sheet specimens and undesired fractures for some strain paths. The results showed that the modified Marciniak test is a more robust method for the FLD determination of thin sheet materials. Nevertheless, in spite of the issues associated with the ASTM standard test for the low thickness sheet, the FLDs determined by the two methods led to similar results. In addition to the experimental approach, the FLD was predicted using a modification of the Parmar–Mellor–Chakrabarty (PMC) model, which incorporates the effect of surface roughness. A non-quadratic anisotropic yield function, Yld2000-2d was implemented in this model to represent the anisotropy of the sheet metals. The FLD predicted with the conventional M–K (Marciniak–Kuczyński) and the modified PMC models were compared to the FLD determined experimentally. The FLD calculated with this modified model was in better agreement with the measured data than that computed with the M–K model for both thin and thick sheets.

► A modified Marciniak test is proposed to determine the FLD of very thin sheet materials.
► Surface roughness plays an important role for the formability of very thin sheet.
► A non-quadratic anisotropic yield function is implemented in the modified model.
► The Parmar–Mellor–Chakrabarty model predicts the experimental data exceptionally well.