Thinning prediction of hole-expansion test for DP980 sheet based on a non-associated flow rule

Abstract

The hole expansion process is widely used in automotive engineering to produce various car parts (e.g., lower arm, trailing arm, control arm, and chassis parts). A numerical study of the hole expansion test for the 3rd generation of advanced high-strength steel sheets is an attractive research topic because of the sheets’ high strength and low formability. This study presents a numerical prediction of the thinning behaviors observed in the hole expansion test for a DP980 sheet using finite element analysis. The experimental data of the tested material obtained from several standard testing methods, including uniaxial tensile, biaxial tensile, and hole expansion tests, are freely supported in the NUMISHEET 2018 conference Benchmark 01. Accordingly, several material models have been developed based on non-associated flow rule (NAFR) by using Hill’s quadratic, Yld2000-2d, and Yoshida polynomial functions to describe the yield and potential surfaces of the tested material. In addition, the Kim-Tuan hardening model is adopted to correctly represent the stress-strain relationship until large strains. Hence, a user-defined material subroutine (UMAT) is developed in Abaqus/Standard package to simulate hole expansion tests using these developed material models. The simulation results reveal that adopting the NAFR theory in the finite element analysis is an efficient method of simulating the hole expansion test. Additionally, the accuracy of the potential surface plays a crucial role in the thinning behavior prediction in the hole expansion simulation. The experimental data obtained from the plane-strain tension tests are recommended for use in calibrating the yield function parameters.