Microscopic and Macroscopic Analysis of the anelastic behavior of steel with regard to springback prediction

例如，在轻量化设计方面，高强度和超高强度钢的使用带来了弹性回弹方面的挑战，从而导致尺寸精度的挑战。虽然已经有大量的研究对这一现象进行了研究，但对其宏观和微观机制及其相互关系的分析还没有一个整体的观点。弹性卸载的滞弹性，即所谓的塑性可逆部分，在微观层面上有不同的解释。相变、实验设置误差、泊松比和位错运动是对观察到的非线性行为的当前假设。然而，这些论证是基于宏观实验，不能证明微观假设。微观研究表明，在原子水平上发生了与宏观行为不同的效应。考虑到金属材料的弹性行为，微观参数如局部位错密度、相变和微观应力与宏观应力-应变行为的耦合到目前为止还缺乏，因此本研究需要进行这项研究。本项目的目的是分析材料IF220和DP1000在加载和卸载过程中的弹性和滞弹性行为，同时考虑轧制方向和预应变，以开发、验证和验证一个全面的和物理上一致的模型来预测板材成形件的回弹。为此，进行了常规拉伸和循环拉伸试验，一方面通过原位中子衍射进行微观评价，另一方面通过光学和触觉应变测量进行宏观评价。作为微观研究的一部分，除了晶格应变外，还利用极图分析了位错密度的变化和织构的发展。这些微观参数是对过程进行物理上一致描述的基础。通过对宏观变形和整体载荷条件的并行、同步测量，可以将微观结果与材料的宏观行为相关联。在考虑预应变和轧制方向相互作用的基础上，建立了加载和卸载模型。最后，将该模型在仿真环境中实现，并通过真实实验进行验证。

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 project is to analyze the elastic and anelastic behavior of the materials IF220 and DP1000 during loading and unloading, taking into account the rolling directions as well as the pre-strain, in order to develop, validate and verify a comprehensive and physically consistent model to predict springback of formed sheet metal components. Normal and cyclic tensile tests are carried out for this purpose and evaluated on the one hand microscopically by means of in situ neutron diffraction and on the other hand macroscopically by optical and tactile strain measurement. As part of the microscopic investigations in addition to the lattice strains, the change in the dislocation density and the texture development is analyzed using pole figures. These microscopic parameters are the basis of a physically consistent description of the processes. The microscopic results can be correlated with the macroscopic material behavior by means of parallel, synchronous measurement of the macroscopic deformation and the global load condition. Based on the interactions including pre-strain and rolling directions, a loading and unloading model is derived. Finally, the model will be implemented into a simulation environment as well as validated and verified using real experiments.