Introducing high strength and ductility twinning induced plasticity (TWIP) steels for European automotive applications through advanced material modeling (TWIP4EU)

The aim of TWIP4EU is to promote the introduction of modern twinning induced plasticity (TWIP) steels as candidate material for production of lightweight automobile components. To introduce a new steel grade like high strength and ductility TWIP-steel for large scale applications in industrial practice, a thorough validation of the material behaviour with useable material laws implementable incommercial finite element codes must be available since numerical simulations are used all along the production process of car body parts. For this purpose, this project proposes a novel and advanced approach towards modelling the deformation and forming behaviour of new TWIP-steels. The project comprises a comprehensive experimental plan combined with the development of a constitutive framework moti vated from micromechanical quantities to describe the deformation behaviour of TWIP-steels. Based on the results from microstructure analyses, macroscopic test and forming experiments the material was extensively characterized. The experimental results were taken into consideration for the development of the constitutive framework. The developed TWIP4EU material model was implemented into two commercially available finite element software packages. Prototype components were successfully produced out of TWIP-steel material. The superior formability of TWIP-steel could be demonstrated. The numerical results which are obtained from simulation using the developed material model are in good agreement with the experimental findings

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

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