Investigation of the micro-structural relationships during the elasto-plastic deformation of steels using dislocation density based crystal plasticity and in-situ diffraction experiments

• Applicants: Dr.-Ing. Christoph Hartmann; Dr. Michael Hofmann; Professor Dr.-Ing. Wolfram Volk
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 573088517

In terms of lightweight design, for example, the use of high and ultra-high strength steels leads to challenges in elastic springback and thus dimensional accuracy. Although a large number of studies have already dealt with this phenomenon, there is no holistic view on the macroscopic and microscopic mechanisms and analysis of their correlation. The anelastic, so called plastically reversible, portion of the elastic unloading is differently explained in the microscopic level. Phase transformations, experimental setup errors, Poission's ratio, and movement of dislocations are current assumptions for the observed nonlinear behavior. However, the arguments are based on macroscopic experiments and cannot prove of the microscopic assumptions. Microscopic investigations have shown that at the atomic level effects occur which differ from the macroscopic behavior. A coupling of microscopic parameters, such as local dislocation densities, phase transformations and microscopic stresses with macroscopic stress-strain behavior considering the elastic behavior of metallic materials, is lacking so far and should therefore be carried out in this research. The aim of this research project is to analyze the elastic and anelastic behavior under loading and unloading, taking into account the rolling direction and the pre-deformation. In addition to the planned in situ diffraction experiments, the research project will focus on crystal plasticity models based on dislocation density. Simple tensile tests, tests with loading and unloading cycles as well as cyclic tensile-compression tests will be carried out for this purpose. These are investigated by microscopic analysis (in situ diffractometry, TEM, EBSD), macroscopic (optical and tactile strain, temperature) measurements and accompanying crystal plasticity simulations, where different inverse characterization methods are explored. The main focus is the cross-scale investigation of the microstructural interactions and their macroscopic effects of the elsato-plastic material behavior of multiphase steels.

• DFG Programme: Research Grants