GOALI: Understanding Light-weight Transparent Ceramic Mechanical Response: From Single Grain Boundary to Bulk Material

透明多晶轻质陶瓷具有独特的加工性能、光学性能和机械性能，使其适用于透明装甲、航空光学和潜艇高压玻璃等应用。不幸的是，这些材料通常表现出比其他玻璃更大的强度变化，使得它们不太适合这种高可靠性应用。这个资助机会学术联络与工业（GOALI）项目是基于这样的假设，即材料晶体之间的边界化学的微小变化对整体机械行为有很大的影响。了解在这些边界上哪些化学成分是有利的，可以改进材料的工程设计，并为高强度光学元件的应用创造新市场。实现这一目标将推进实验力学;促进国家健康，繁荣和福利;并确保国防。为了建立这一假设，必须对尺寸范围从人类头发宽度的1/100（测量单晶边界）到整个组件尺寸的样品进行机械测试和模拟。 直到最近，新开发的测试方法才使这种实验变得可行，从而为理解这一问题创造了新的机会。作为该项目的一部分，学生实习将在工业合作伙伴提供，代表性不足的本科生将被招募到研究小组，未来的女学生将通过女孩学习材料营活动的动机。大格式MgAl 2 O 4尖晶石的机械强度表现出相当大的可变性，这是假设导致晶界化学计量和化学的局部变化。 然而，颗粒的几何形状，晶界各向异性和晶界化学的变化，使相关的简单指标，如平均边界组成和平均强度的挑战。为了对尖晶石的机械行为有一个机制性的理解，这项工作将实验相关的长度尺度连接起来：从测量单一边界上的断裂特性和晶界化学到预测大样本的断裂强度及其特性分布。该项目开发了数字粒子跟踪方法，用于在透射电子显微镜中原位进行的单晶界断裂实验期间绘制演变应变。从相关的有限元分析开发的内聚区模型可以与测得的晶界化学和取向差。在中尺度（几十个晶粒）上可以观察到作为各向异性函数的晶界和体积性质分布。这使我们能够定义代表性的体积元素，用于宏观样品的连续分析。 在这个尺度上，实验上合理的成分梯度、残余应力梯度和晶界性质分布将被用来预测宏观强度的分布。该奖项反映了NSF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。

Transparent polycrystalline light-weight ceramics provide a unique combination of processibility, optical properties, and mechanical properties making them suitable for applications as transparent armor, optics for aviation, and high-pressure glass for submarines. Unfortunately, these materials often exhibit greater variations in strength than other glasses, making them less suitable for such high-reliability applications. This Grant Opportunities for Academic Liaison with Industry (GOALI) project is based on the hypothesis that minor changes in chemistry at the boundaries between material crystals have a large effect on the overall mechanical behavior. Understanding what chemistry is favorable at these boundaries could allow for improved engineering of the material and create new markets for applications as a high strength optical element. Achieving this goal will progress experimental mechanics; advance the national health, prosperity, and welfare; and secure the national defense. To establish this hypothesis, mechanical testing and simulation must be performed on samples ranging in size from 1/100th of the width of a human hair (to measure single crystal boundaries) to the size of the entire component. Newly developed testing methods have only recently made such experiments feasible, thus creating new opportunities to understand this problem. As part of the project, student internships will be provided at the industrial partner, underrepresented undergraduate students will be recruited in the research group, and prospective female students will be motivated through Girls Learning about Materials Camp activity.The mechanical strength of large-format MgAl2O4 spinel exhibits considerable variability that is hypothesized to result from local variations in grain boundary stoichiometry and chemistry. However, the granular geometry, grain boundary anisotropy, and variations in grain boundary chemistry make relating simple metrics like average boundary composition and average strength challenging. To develop a mechanism-informed understanding of the mechanical behavior of spinel, this work bridges experimentally relevant length scales: from measuring fracture properties and grain boundary chemistry on single boundaries to predicting the fracture strength of large specimens and their property distributions. The project develops digital particle-tracking methods for mapping evolving strain during single grain boundary fracture experiments performed in situ in a transmission electron microscope. Cohesive zone models developed from associated finite element analyses can be correlated with measured grain boundary chemistries and misorientations. Grain boundary and bulk property distributions as a function of anisotropy can be observed at the mesoscale (dozens of grains). This allows us to define representative volume elements for use in a continuum analysis of the macroscopic samples. At this scale, experimentally reasonable compositional gradients, residual stress gradients, and grain boundary property distributions will be used to predict the distribution of macroscopic strength.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.