Modeling differential permanent softening under strain-path changes in sheet metals using a modified distortional hardening model

Abstract In this study, a modified distortional hardening model is proposed based on the homogeneous yield-function based anisotropic hardening (HAH). An improvement is made to capture differential permanent softening (DPS) under strain-path changes in sheet metals, whereas the other anisotropic hardening features such as the Bauschinger effect, transient behavior, and cross hardening phenomenon are retained as they are in the original HAH model. The modified HAH (M-HAH) model is implemented in a commercial finite element software using the user-defined material subroutine, and validated well by reproducing the flow stress behaviors after differently programmed strain-path changes for dual-phase steel, extra deep drawing quality steel, and ferritic stainless steel. Additionally, the M-HAH can simulate the DPS in two-step tension tests, which cannot be accurately modeled by the original HAH. Finally, the V-bending springback tests with pre-tensioned specimens are evaluated with different modeling schemes including the classical isotropic hardening, kinematic hardening and distortional hardening models.