Macroscopic modelling and simulations of material behaviour of modern twinning-induced plasticity steels

TWinning-induced plasticity (TWIP) steels are considered to be prospective materials for production of lightweight automotive components due to their extraordinary ductility at high tensile strength. To introduce new TWIP steels for large scale applications in industrial practice, a thorough validation of the material behaviour with suitable material laws implementable in commercial finite element (FE) codes must be available. The paper deals with the modelling of the macroscopic behaviour of TWIP steels with the further aim of simulating metal forming processes and representing the component behaviour in commercial FE packages. To this end, a constitutive framework for the accurate characterization of TWIP steels under large plastic deformations has been developed. The well-known physical ly-based Bouaziz-Allain approach [2] has been proven to be adequate for the description of the flow behaviour of TWIP steels and has been considered as a base model for the current research. This one-dimensional model computes monotonic uniaxial tensile stress-strain curves on the basis of the evolution of the dislocation density and the twin volume fraction. In order to include the influence of stress state and kinematic hardening the original Bouaziz-Allain model has been modified and an extended three-dimensional elasto-plastic formulation has been developed and implemented computationally in commercial FE codes ABAQUS/Explicit, LS-Dyna and PAM-STAMP as user subroutines. The results of the mechanical and microstructural analysis of a new preseries TWIP steel grade produced by Salzgitter AG have been used as input for the material modelling. The model has been calibrated by means of numerical tests and shows a good agreement with the experimental data.