Analysis of elastic-plastic material behavior of high-strength steel materials under cyclic and swelling loading as a function of relaxation behavior

• Applicant: Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 519039020

The objective of the proposed research project is to analyze the elastic-plastic material behavior under cyclic and discontinuous loading of high-strength steel materials. In addition to a pronounced Bauschinger effect, these materials exhibit nonlinear elastic material behavior under swelling loading. By modeling these properties and investigating the underlying cause-effect relationships, the numerical prediction of sheet metal forming processes with high-strength steels will be improved. Both effects have a significant influence on the springback occurring after a forming process, but have so far only been taken into account independently of each other in a simulative design of components in basic scientific investigations. Metal-physical approaches exist to explain both effects, although research into the interrelationship of the two characteristics is necessary for clear assignment. The analysis of a possible correlation of both mechanisms as well as the influence of relaxation effects, i.e. a time-dependent stress behavior under constant load application, represent key aspects for improving the understanding of materials and thus the numerical description. The hypothesis of the project is that there is a systematic relationship between material properties, such as nonlinear elasticity, the Bauschinger effect and relaxation processes. In the first phase of the project, the mechanical behavior of the material is analyzed under cyclic and pulsating loads, with continuous and discontinuous load application, in order to investigate the functional relationships between the aforementioned effects in the subsequent work packages. Here, the material-specific influence of the stress state, the anisotropy, the pre-strain as well as the load and unload phases will be investigated. In order to be able to determine the causes of identified interactions, microstructural characterizations will also be carried out with the aid of scanning electron microscopy and X-ray diffraction investigations. The evaluation of the results in work phase 2 with regard to the occurring mechanisms of action will improve the understanding of the material. Furthermore, mechanical parameters for the description of the Bauschinger effect and the relaxation behavior will be derived, which will provide new approaches for plastomechanical modeling. The subsequent significance evaluation of the effects as well as the adaptation of existing material models should improve the numerical prediction of the springback. Finally, the validity of the derived conclusions and modeling approaches will be verified in a near-process laboratory test.

• DFG Programme: Research Grants