Calibration of the Flow Curve Up to Large Strain Range by Incremental Sheet Forming Coupled with FEM Simulation

Abstract

Conventionally, a stress–strain curve for sheet materials is defined by the uniaxial tensile test; however, it is limited by the necking phenomena. The stress–strain curve in the post-necking range is determined using common hardening equations, such as the Swift or Voce equation. Nevertheless, the accuracy of this flow curve in the extrapolation range is questionable. In this study, the inverse method using incremental sheet forming coupled with FEM simulation was used to calibrate the stress–strain curve up to a large strain range. In the incremental sheet forming experiment, the forming force was monitored in the whole process until fracture. Then, FEM simulation by ABAQUS/Explicit was performed using the incremental stress–strain curve, accompanied by Hill’s 1948 yield behavior. The incremental stress–strain curve was calculated using the β parameter, which was systematically assigned to adjust the trial stress at each strain increment of the FEM process. The correct incremental stress–strain curve was determined when the force prediction was in good agreement with the experiment.