Deformation behaviour of TWIP-Steels: From experiments to constitutive modelling and simulations

High manganese content TWIP (TWinning Induced Plasticity) steels represent one of the most prospective materials for production of lightweight automobile components due to their extraordinary ductility at high tensile strength. In order to analyze the complex deformation behaviour and forming limits of these steels under different loading conditions, a variety of tests including tensile tests with variation of specimen orientation, strain rate and temperature, tension-compression tests, tensile tests with prestraining in cross direction, bending-under-tension tests, shear tests, bulge tests, Nakajima tests, and square cup drawing tests were performed. Since the material behavior of TWIP-steels is essentially a result of the micromechanical effects, extensive experimental studies were also undertaken on microscale. Here scanning and transmission electron microscopy investigations were used to systematically analyze and quantify the twinning effect. In order to include the influence of different loading conditions and kinematic hardening (Bauschinger effect) on the material behavior the physically-based Bouaziz-Allain model has been modified and an extended tensorial formulation has been developed and implemented as user subroutines in commercial FE codes. The model has been calibrated by means of numerical tests and has shown a good agreement with the experimental data.