Two-surface plasticity Model and Its Application to Spring-back Simulation of Automotive Advanced High Strength Steel Sheets

Abstract

A two‐surface isotropic‐kinematic hardening law was developed based on a two‐surface plasticity model previously proposed by Lee et al., (2007, Int. J. Plast. 23, 1189–1212). In order to properly represent the Bauschinger and transient behaviors as well as permanent softening during reverse loading with various pre‐strains, both the inner yield surface and the outer bounding surface expand (isotropic hardening) and translate (kinematic hardening) in this two‐surface model. As for the permanent softening, both the isotropic hardening and the kinematic hardening evolution of the outer bounding surface were modified by introducing softening parameters. The numerical formulation was also developed based on the incremental plasticity theory and the developed constitutive law was implemented into the commercial finite element program, ABAQUS/Explicit and ABAQUS/Standard using the user‐defined material subroutines. In this work, a dual phase (DP) steel was considered as an advanced high strength steel sheet and uni‐axial tension tests and uni‐axial tension‐compression‐tension tests were performed for the characterization of the material property. For a validation purpose, the developed two‐surface plasticity model was applied to the 2‐D draw bending test proposed as a benchmark problem of the NUMISHEET 2011 conference and successfully validated with experiments.