Effects of Anisotropic Yield Functions on the Accuracy of Forming Simulations of Hole Expansion

Abstract

The deformation behavior of a high strength steel sheet in hole expansion tests using a flat-bottomed cylindrical punch has been investigated both experimentally and analytically to clarify the effects of anisotropic yield functions on the accuracy of finite element simulations of hole expansion. The material used in the hole expansion tests is a high strength steel with a tensile strength of 590MPa. The elastic-plastic deformation behavior of the test material has been precisely measured by biaxial tensile tests using cruciform specimens to determine the appropriate anisotropic yield function for the test material. The measured contours of plastic work and the directions of plastic strain rates are in good agreement with those predicted using the Yld2000-2d yield function with an exponent of 6. Moreover, forming simulations and experiments on the hole expansion of the test material have been carried out. The anisotropic yield functions used in the simulation are von Mises, Hill's quadratic and Yld2000-2d non-quadratic yield functions. The result of forming simulations by the Yld2000-2d yield function with an exponent of 6 has given the closest agreement with the experimental ones. It was found that the yield functions significantly affect the predictive accuracy of the deformation behavior of the steel sheet subjected to hole expansion.