Analysis of the anisotropy influence on quasistatic and cyclic deformations of nickel base alloys by combining FEM methods with variational image processing

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Our project aims to investigate the influence of local anisotropies on the elastic and plastic behavior as well as initial fatigue damage in polycrystalline Ni-base alloys by combining in situ deformation experiments, innovative image analysis methods and FEM simulations. The fatigue behavior of Ni-base alloys is strongly influenced by their intrinsic, compared to other metallic materials exceptionally pronounced, elastic anisotropy, which strongly affects stress and strain distribution in the polycrystalline microstructure. Direct correlation between experiment and simulation in the engineering part will be assured by in situ testing of sheets made of the Ni-base alloy Inconel 617 with thicknesses below the average grain size. Characterization by SEM/EBSD at both flat sides of the gauge section provides direct correlation of the local, quasi 2D grain structure with the strain distributions computed by image analysis via variational flow and deformation models. In the mathematical part, variational models for multimodal SEM/EBSD images from in situ tested specimens will be developed for preprocessing the data as well as for providing strain measurements and damage detections. The strain fields computed by the variational model will be compared to FEM simulations with identical initial grain morphology. This allows verification and, if needed, optimization of the FEM models. Based on this, the validated FEM model is used for systematic parameter studies of grain structures with different morphologies to understand the influence of grain neighborhood effects as well as different textures. Fatigue tests at thin flat samples accompanied by thorough SEM analysis serve to correlate strain concentrations and associated grain morphologies with fatigue damage processes. Our interdisciplinary investigations will provide a deeper understanding of the influence of grain orientation and elastic anisotropy on the local deformation behavior of Ni-base superalloys, determined by FEM in conjunction with variational image processing, and the correlation of local deformation with the fatigue damage of the material. This allows, from the applicants’ point of view, substantial progress compared to the actual state-of-the-art, both, from the viewpoint of methodology and understanding of the investigated material class.