The high-strength steel sheet forming limit curves predicted on strain and stress and their utilization to automotive forming parts

In this work, experimental investigations and numerical finite element simulations of the high-strength steel (HSS) sheet dual-phase 440 (DP440) were conducted to determine the forming limit curve (FLC) and forming limit stress curve (FLSC). The Nakajima stretching forming examination was performed using a universal tensile testing machine to resolve the FLC experimentally. Afterwards, the Marciniak-Kuczinsky (M-K) model was used to prescribe numerical finite element simulation methods for both the FLC and the FLSC. Furthermore, anisotropic yield criteria (Hill's 48 and Yld2000-2d) were used to determine the plastic deformation behavior of the HSS sheets and their FLSCs using the experimentally obtained FLC forming data. The Swift hardening law was used in the stress-strain curve, and the effects of the anisotropic yield models on the FLCs and FLSCs analyzed by numerical finite element simulations were determined. The plasticity-determined FLSC was influenced by the anisotropic criteria model. The FLC and FLSCs were computed using the M-K model, the Swift hardening law, and the Yld2000-2d yield criterion. They were more precisely predicted experimentally than using the Swift hardening law and Hill's 48 yield criterion. The effects of different yield models on the anisotropic plastic flow curve behavior in bumper shell bar forming were investigated. We found that the stress-based FLCs, rather than strain-based FLCs, better represented the formability of HSS sheets. Therefore, the Yld2000-2d yield model better represented the anisotropic behavior of the HSS sheet DP400 than Hill's 48 yield model, and can suitable be used for the analysis prediction and design of automotive parts under forming processes.