Applying a New Generalized Anisotropic Distortional Hardening Model to Analyse the Springback Behaviour of 1.8 GPa Sheet Metal in Cold Roll Forming

The roll forming process effectively reduces sheet metal springback through multi-pass local plastic strain accumulation and residual stress reconstruction. This paper extends previous work that developed a generalized anisotropic distortional hardening (G-ADH) model based on the associated flow rule. Considering the relationship of shear stress and uniaxial tension stress for 1.8GPa steel, the analytical Poly6-I is used. To accurately predict springback in ultra-high strength sheet in nonlinear loading path, the G-ADH model with Young's modulus degradation is used. For comparison, the Chaboche model is also used to predict the loading-reverse loading curves. The results show that the G‑ADH model offers greater flexibility and higher accuracy than the Chaboche model. To further verify the validity of these models, the springback obtained from cold roll‑forming experiments on U‑shaped sections of 1.8GPa steel is employed. The experimental and numerical results demonstrate that, regardless of the presence of side rolls, the “G-ADH + Poly6-I” model considering Young's modulus exhibits high consistency with experimental data in predicting springback with relative errors below 1.5%, which is attributed to simultaneous description of reverse-loading hardening and degradation of the unloading modulus. The springback differs at different profiles perpendicular to the sheet length direction, which originates from the inconsistency in the extent of the local plastic deformation zones. Lower springback is observed during the forming process that includes side rolls. This study reveals the correlation between the springback amplitude and the accumulation of equivalent plastic strains under low stress during U rolling forming of 1.8GPa steel, providing an accurate numerical tool for predicting and reducing springback of ultra-high strength alloys under bending-unloading-reverse bending deformation paths.