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

本项目旨在通过原位变形实验、创新的图像分析方法和有限元模拟相结合的方法，研究局部各向异性对多晶镍基合金弹塑性行为以及初始疲劳损伤的影响。与其他金属材料相比，镍基合金的疲劳行为受其固有的弹性各向异性的强烈影响，而弹性各向异性对多晶组织中的应力和应变分布有很大的影响。通过对厚度低于平均晶粒度的镍基合金Inconel617制成的板材进行现场测试，将确保工程部分的实验和模拟之间的直接关联。通过扫描电子显微镜/电子背散射谱(SEM/EBSD)在规范截面两侧的表征，提供了局部准2D晶粒结构与通过变分流动和变形模型通过图像分析计算的应变分布的直接关联。在数学部分，将建立来自现场测试试件的多模式扫描电子显微镜/EBSD图像的变分模型，以对数据进行预处理以及提供应变测量和损伤检测。将变分模型计算的应变场与具有相同初始晶型的有限元模拟结果进行比较。这允许对有限元模型进行验证，并在需要时进行优化。在此基础上，利用验证后的有限元模型对不同形貌的晶界组织进行了系统的参数研究，以了解晶界效应以及不同织构对晶界结构的影响。在薄扁平试件上进行的疲劳试验，伴随着彻底的扫描电子显微镜分析，可以将应变浓度和相关的颗粒形态与疲劳损伤过程相关联。我们的跨学科研究将使我们更深入地理解有限元结合变分图像处理确定的晶向和弹性各向异性对镍基高温合金局部变形行为的影响，以及局部变形与材料疲劳损伤的关系。从申请人的角度来看，这使得无论是从方法的角度还是从对所调查的材料类别的理解来看，与实际最先进的技术相比都取得了实质性的进步。

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.