New material model available for HSD® steel
29.06.2016 | Initiative Automotive
New material model available for HSD® steel
As a part of an EU-funded project, a new material model has been developed for the PAM-STAMP and LS-DYNA software programs that better reflects the outstanding forming characteristics of the Salzgitter Flachstahl GmbH HSD® steel than conventional models do.
Iron-manganese steels have characteristics that allow them to stand out from conventional steels. They have a combination of formability and strength that has never been achieved before. This is also indicated in the brand name: "High Strength and Ductility®", or HSD® for short. For example, HSD®600, which has a yield strength of at least 600 MPa and tensile strength of more than 1,000 MPa, achieves elongation at break of 50%.
These outstanding characteristics are achieved thanks to the high manganese content and additions of aluminum and silicon. Thanks to this alloy concept, an austenitic microstructure develops during production. So-called "twins" form in the microstructure during the forming. This is a special kind of dislocation formation that decisively determines the forming and hardening behavior. This is called "twinning-induced plasticity", or TWIP for short. When this special behavior is to be depicted by means of numerical simulation, it is necessary to test the prevalent material models for their forecast quality. A certain level of imprecision is seen here, particularly in the simulation of very large degrees of deformation with a simple material model. This prompted Salzgitter Mannesmann Forschung (SZMF), together with Fraunhofer IWM Freiburg as project coordinator, the DYNAMORE and ESI software firms, and automotive seating manufacture Faurecia, to develop a material model appropriate for these steel grades in the framework of a European research project. The project, named, "Introducing high strength and ductility twinning induced plasticity (TWIP) steels for European automotive applications through advanced material modeling“, or TWIP4EU, was funded by the "Research Fund for Coal and Steel". The final report (RFSR-CT-2012-00019) will be available in autumn 2016.
The TWIP4EU material model developed in this consortium takes into account the formation and interaction of the twins as a fundamental strengthening mechanism for these steels. The density of the twins here can be output as a result quantity for the component that is to be simulated. Twins form in the steel to a greater or lesser extent, depending on the loading conditions. Further shaping can cause them to impede or interfere with one another. This effect leads to hardening that depends on the load. The manifestation of this anisotropic hardening can be adapted to the particular steel grades in proportion to the otherwise customary isotropic hardening. In order to be able to determine the correct parameters here, various forming procedures were carried out. The strain distributions and processing forces were measured and enlisted for detailed comparison with the simulation. The tests were conducted in correspondence with HSD®600 from Salzgitter Flachstahl GmbH, so that the TWIP4EU model already contains the right parameters for it while being adaptable for other steels.
TWIP4EU project demonstrator:
Side of seat backrest from Faurecia Autositze GmbH
Effective strains of more than 120%
HSD®600 1.4 mm from Salzgitter Flachstahl GmbH
If you are interested in the TWIP4EU material model, you can contact support.esigmbh@esi-group.de with regard to PAM-STAMP or support@dynamore.de with regard to LS-DYNA.
If you are interested in the material or corresponding simulations but are still in an early component development phase and do not yet require high precision, you can also obtain characteristics or material cards directly at werkstoffkennwerte@salgitter-ag.de.