Assessment of crystal-plasticity simulation: Plastic behaviors in biaxial stress states and cylindrical deep drawing

Abstract

This study investigates the predictive accuracy of a crystal-plasticity finite-element method for plastic behavior in uniaxial and biaxial stress states as well as the cup height and limiting drawing ratio (LDR) in cylindrical deep drawing. The R value, which is the ratio of width-to-thickness plastic strains, significantly affects the cup height, while the flow stresses in the plane-strain tension and tensile–compression combined stress states determine the LDR. Experiments and crystal-plasticity simulations of uniaxial tension and various biaxial stress tests are conducted. Custom-designed antibuckling plates are used to simultaneously apply tension and compression to sheet specimens. The crystal-plasticity simulation accurately predicts the R values and the flow stresses for the plane-strain tension and tension–compression biaxial stress states when the strain was less than 0.05. In the cylindrical deep drawing simulations, cups are safely drawn when the drawing ratio ranges from 1.8 to 2.0, and the strain localization is predicted at the bottom of the cup wall when the draw ratio is 2.1 or higher. Both the experiments and simulations yield an LDR of 2.0. When the drawing ratio is between 1.8 and 2.0, the predicted cup heights agree with the experimental results. Therefore, the crystal-plasticity simulation accurately predicts the mechanical properties of the specimen as well as the cup height and LDR in cylindrical deep drawing. Although the crystal-plasticity model predicts the LDR accurately, it overestimates the formability. In the large-strain range, the crystal-plasticity model overestimates the work hardening and predicts the higher formability. We found that the anisotropic hardening in the large-strain range is crucial to further improve the accuracy of crystal-plasticity simulations.