The plastic flow analysis of cold strained DC04 ferritic steel using BBC family yield functions under associated flow rule and non-associated flow rule concepts

Abstract

This study compares the mechanical properties of numerically predicted anisotropic parameters (using the BBC family of models) and experimentally measured results for DC04 steel sheets. The evolution of mechanical properties—such as flow stresses and Lankford coefficient—was analysed during initial plastic anisotropy and mechanical strain hardening in material forming. The results show that the evolution of mechanical properties under isotropic work hardening was predicted with respect to the selected strain levels during tensile testing of the steel. A proposed regression model effectively described the yield stress and r-value behaviour. The Lankford parameter was determined as an instantaneous value based on polynomial fitting of the transverse versus longitudinal true plastic strain curve. Using 08 and 16 independent orthotropic parameters, the BBC criteria family (2003_8p, 2005_8p, 2008_8p, and 2008_16p) was formulated and tested under a non-associated plasticity framework across different material orientations relative to the sheet's rolling direction. Vickers hardness was determined by hardness testing and measuring the two diagonal indentations. The aspect ratio, defined as the ratio of diagonal lengths in the longitudinal direction to those in the thickness direction, was linked to the Lankford coefficient. A strong correlation was observed between experimental hardness measurements and the material's anisotropic properties.