Using Micromechanical Experiments to Investigate the Rheology of Geologic Materials

地质物质的物理和化学性质控制着地球表面和内部的发展。流变学是材料性质研究的一个特殊的分支，它表征了材料的流动或粘性变形的能力。地质物质的流变性主要控制地幔对流、板块构造和山脉的形成。因此，流变学与许多自然灾害（如地震、火山和海啸）以及自然资源的生产直接相关。在这个项目中，研究人员正在使用材料科学的工具来了解构成地壳和上地幔大部分的矿物的流变学。从这项研究中获得的数据将使地球科学家能够更好地了解板块构造在地球和其他行星上的作用方式。该研究项目通过妇女充分参与STEM，通过公众宣传提高公众科学素养和公众参与STEM，通过本科生和研究生培训培养有竞争力的STEM劳动力，以及改善实验室以加强研究基础设施，来推进预期的社会成果。该项目的目标是使用微力学方法研究地质材料的粘塑性流变学，包括纳米压痕和微柱压缩测试。在纳米压痕测试中，用精确控制的力将锋利的压头推入感兴趣的样品中，通常达到数十至数百纳米的深度。力和位移的同时记录用于评估测试样本的弹性和塑性响应。在微柱压缩测试中，使用聚焦离子束制造直径小至几百纳米的材料柱。使用配备有圆柱形探针的纳米压痕仪，进行单轴压缩测试，以确定在一系列变形条件下的微柱的机械响应。在本项目中，将在低温至中等温度（T = -10至600摄氏度）下对石英、斜长石、斜方辉石和橄榄石的定向单晶进行微机械变形实验。从这些实验中获得的数据将被用来约束岩石圈的条件下，矿物的流变学是强大的和低温塑性预计是占主导地位的变形机制。流变各向异性的影响将使用相同的微观力学方法进行评估。实验结果将得到高分辨率像差校正扫描透射电子显微镜成像和电子能量损失谱的补充，以提供对变形引入的晶体缺陷的原子尺度结构和化学的洞察。

The physical and chemical properties of geologic materials control the development of Earth's surface and interior. Rheology is one particular branch of the study of material properties, which characterizes materials' ability to flow or deform viscously. The rheology of geologic materials is mainly responsible for controlling mantle convection, plate tectonics, and the formation of mountains. As such, rheology is directly related to numerous natural hazards such as earthquakes, volcanoes, and tsunami, as well as the production of natural resources. In this project, the investigators are using tools from materials science to understand the rheology of minerals that make up the bulk of Earth's crust and upper mantle. The data that result from this study will allow geoscientists to better understand how plate tectonics works, both on Earth and on other planetary bodies. The research project advances desired societal outcomes by full participation of women in STEM, public outreach to increase public scientific literacy and public engagement with STEM, development of a competitive STEM workforce through undergraduate and graduate student training, and laboratory improvement that enhances infrastructure for research.The objective of this project is to investigate the viscoplastic rheology of geological materials using micromechanical methods, including nanoindentation and micropillar compression testing. In a nanoindentation test, a sharp indenter is pushed into a specimen of interest with a precisely controlled amount of force, typically to depths of tens to hundreds of nanometers. A simultaneous record of the force and the displacement is used to assess the elastic and plastic response of the test specimen. In a micropillar compression test, a column of material with a diameter as small as a few hundred nanometers is fabricated using a focused ion beam. Using a nanoindentation instrument equipped with a cylindrical probe, uniaxial compression tests are performed to determine the mechanical response of the micropillar over a range of deformation conditions. In this project, micromechanical deformation experiments will be performed at low to moderate temperatures (T = -10 to 600 degrees C) on oriented single crystals of quartz, plagioclase feldspar, orthopyroxene, and olivine. Data from these experiments will be used to constrain the rheology of minerals under conditions where the lithosphere is strong and low-temperature plasticity is predicted to be the dominant deformation mechanism. The effects of rheological anisotropy will be assessed using the same micromechanical methods. Experimental results will be complemented by high resolution aberration-corrected scanning transmission electron microscope imaging and electron energy loss spectroscopy to provide insight into the atomic-scale structure and chemistry of crystalline defects introduced by deformation.