nce and Modelling

Contributed talk

Virtual material testing for the improved parameter identification of anisotropic yield functions and its application to sheet metal forming simulations

Alexander Butz, Fraunhofer IWM, Freiburg, Germany
Maria Baiker, Fraunhofer IWM, Freiburg, Germany
Jan Pagenkopf, Fraunhofer IWM, Freiburg, Germany
Dirk Helm, Fraunhofer IWM, Freiburg, Germany

For the simulation of forming processes, experimental data is required to calibrate the parameters of the chosen materials model. With respect to sheet metal forming simulations, an essential part of the model is the accurate description of the anisotropic elasto-plastic material behavior. Due to the texture development during the production process, sheet metals often show a significant anisotropy with respect to yielding and also with respect to the Lankford coefficient. On the other hand, to determine the parameter of more sophisticated models a large number of experiments is needed that is to some extent very difficult to realize. A promising approach is to extend experimental data by numerical data obtained from so-called “virtual testing”.

For this “virtual testing” a crystal plasticity based full-field microstructure simulation approach is used to virtually determine the mechanical properties of sheet metals. Microstructural features like the specific microstructure morphology and the crystallographic texture are taken into account in order to represent the plastic anisotropy. This virtual testing allows the study of arbitrary but clearly defined loading conditions applied to a polycrystalline material. In this contribution, a special focus is on the determination of the Lankford coefficients and on the yield surface under plane stress conditions.

Compared to experimental procedures virtual materials testing allows the generation of significantly more data points on the yield surface. This data is used to precisely calibrate anisotropic elasto-plastic materials models which are commonly used for sheet metal forming simulations. The accuracy of this approach is demonstrated for a high strength steel grade and an aluminum alloy by comparison with results from forming experiments.

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