Forward Model Based Strain Analysis in Highly Deformed Metallic Systems Using Electron Back-Scatter Diffraction Patterns

在工程应用中使用金属和合金需要对这些材料在受到导致其变形的应力时的行为有透彻的了解。虽然变形有时可以用肉眼看到，但实际的变形过程发生在非常小的长度尺度上，这就需要使用高倍率的电子显微镜。本研究将开发一种新的实验技术来高精度地测量这些变形。这些详细的测量将有助于我们理解材料是如何变形的，最终，这将影响金属和合金在整个社会的结构应用中如何安全使用。在这个项目中开发的所有技术都将通过出版物和开源代码的形式提供给社区。该项目还将探索通过众包方式制作免费大学水平教科书的可能性；这个“开放章节”项目将把多个作者撰写的单个章节组合成可定制的按需教科书，这些教科书将免费提供给大学生和整个社会。技术概述现代工程材料通常具有复杂的多相微观结构，这使得很难准确预测它们在外加应力影响下的行为。材料变形行为的许多方面仍然知之甚少。从变形的多晶样品中提取晶格应变是一项困难的工作，需要重新关注，因为新的探测器系统的可用性，特别是电子背散射衍射（EBSD），这是所提议的程序选择的工具。PI和他的团队将采用基于物理的模型来预测EBSD模式，并将变形张量纳入模式生成算法的新功能。结合最近开发的索引算法，将开发一种新的方法，通过将完整的模拟EBSD模式与其实验版本进行匹配来确定变形张量分量，在大样本区域上的预期应变分辨率优于0.0001。这个程序有可能推进我们对现代工程材料以及低对称性地质样品的微观和纳米尺度变形机制的理解。灵敏的EBSD探测器与改进的标引方案相结合，为EBSD数据全模式匹配的常规应变场测定奠定了基础。这些算法将以同行评审的出版物和开源代码的形式提供给社区。在教育方面，OpenChapters项目将通过创建一种开源机制，通过众包的方式生成免费的教科书，从而解决教科书成本迅速上升的问题。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYThe use of metals and alloys in engineering applications requires a thorough understanding of how these materials will behave when they are subjected to stresses that cause them to deform. Although the deformations can sometimes be visible to the naked eye, the actual deformation processes take place at very small length scales, which necessitates the use of electron microscopes operated at high magnification. This research will develop a new experimental technique to measure these deformations with high accuracy. Such detailed measurements will contribute to our understanding of how materials deform, and, ultimately, this will impact how metals and alloys can be used safely in structural applications throughout society. All techniques developed in this program will be made available to the community through publications and in the form of open source code. The PI will also explore the possibility of generating free college-level text books via a crowd-sourcing approach; this "OpenChapters" project will combine individual chapters written by multiple authors into customizable on-demand text books that will be freely available to college students as well as to society at large.TECHNICAL SUMMARYModern engineering materials often have a complex multi-phase microstructure that makes it difficult to accurately predict how they will behave under the influence of an applied stress. Many aspects of the deformation behavior of a material are still poorly understood. The extraction of lattice strains from deformed polycrystalline samples is a difficult undertaking that requires renewed attention due to the availability of new detector systems, in particular for electron back-scattered diffraction (EBSD), the tool of choice for the proposed program. The PI and his group will employ a physics-based model for the prediction of EBSD patterns and incorporate a new capability to include the deformation tensor in the pattern generation algorithm. In combination with a recently developed indexing algorithm, a new approach will be developed to determine the deformation tensor components by matching complete simulated EBSD patterns against their experimental versions, with an anticipated strain resolution of better than 0.0001 over large sample areas. This program has the potential to advance our understanding of micro- and nano-scale mechanisms of deformation in modern engineering materials as well as in lower symmetry geological samples. The combination of sensitive EBSD detectors with a modified indexing scheme will lay the foundation for the routine determination of strain fields by full-pattern matching of EBSD data. The algorithms will be made available to the community in peer-reviewed publications and as open source code. On the educational side, the OpenChapters project will address the rapidly rising cost of text books by creating an open source mechanism for the generation of free text books by a crowd-sourcing approach.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.