Abstract
To evaluate the prediction accuracy of the anisotropic yield function, we propose an original cruciform hole expansion test. Displacements on two axes were applied to the cruciform specimens with a hole in the center. The thickness strain in the region near the hole was compared to the simulation results. Because this forming test is free of friction and bending, it is an appropriate method to assess the anisotropic yield function without the influences of friction or the Bauschinger effect, or the need to consider the stress-strain curve in high-strain region. Hill1948, YLD2000-2D, and spline yield function which is an improved version of the Vegter model were selected, and 6000 series aluminum alloy sheets (A6116-T4) were used in this study. The parameter identification method of the spline yield function also proposed in this paper using the pseudo plane strain tensile test and optimization software. As a result, the spline yield function has better predictive accuracy than the conventional anisotropic yield functions Hill1948 and YLD2000-2D.
Highlights
High-tensile-strength steel sheets and aluminum alloy sheets are used for weight reduction of car bodies
To evaluate the prediction accuracy of the anisotropic yield function, we propose an original cruciform hole expansion test
Hill1948, YLD2000-2D, and spline yield function which is an improved version of the Vegter model were selected, and 6000 series aluminum alloy sheets (A6116-T4) were used in this study
Summary
High-tensile-strength steel sheets and aluminum alloy sheets are used for weight reduction of car bodies. It is difficult to validate anisotropic modeling by only considering the change in thickness distribution This hole-expansion test is relatively simple, but includes contacts between the material and the dies, as well as bending and back-bending deformation. In addition to the anisotropic hardening, Suzuki et al [12] considered the Bauschinger effect using the Yoshida-Uemori model [13] and the stress-strain curve in the high-strain region, which was obtained from a plane bending test using a biaxial tensile machine. To validate the yield function, biaxial tensile tests were conducted using cruciform specimens with a hole in the center Because this forming test does not include friction and bending, it is possible to a quantitatively compare the experimental and simulation results
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