Testing Stress Percolation as a Model for Stress Transmission in Rocks

测试应力渗透作为岩石中应力传递的模型

• 批准号: 1417218
• 负责人: Pamela Burnley
• 金额: $ 32.8万
• 依托单位: University of Nevada Las Vegas
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1417218&HistoricalAwards=false
• 关键词: Testing; Stress; Percolation; Model; Transmission

This project will test stress percolation hypothesis and its utility for working with geologic materials. Both scientists and engineers have assumed that when a rock is loaded by either tectonic forces or within the context of engineering projects, the load is borne evenly throughout the rock. The PI has developed an alternative hypothesis that the stresses produced by external loads on a rock are distributed throughout the rock according to a pattern that resembles the pattern created by water flowing through otherwise dry sand. If the hypothesis proves correct, then stress distribution in rocks will join a large class of phenomena that exhibit 'percolation' behavior, including the patterns of stress distribution observed in granular materials. Thus one implication of the hypothesis is that there is a single unifying physical model for deformation of all earth materials. The value in understanding the stress distribution in rocks is that it will allow us to create better models of rock deformation and better predict the mechanical behavior of rocks, which has implications for deepening our understanding of a variety of Earth processes as well engineering applications. The existence of stress percolation and a refined understanding of how it operates in rocks has tremendous implications for many disciplines beyond geophysics. Researchers in materials science, metallurgy, and shock physics, all struggle with the so called 'polycrystalline problem' - like rocks, many solid materials are composed of aggregates of crystalline grains with a variety of properties. Understanding the response to loading of many of these materials has presented challenges similar to those experienced by those working on rock deformation. Thus, this research will contribute to a better understanding of mechanical problems in all of these disciplines. Using finite element (FEM) simulations of a polycrystalline material the PI has recently shown that local variations in stress and strain participate in large-scale patterns, likely caused by stress percolation. The patterns are a function of the heterogeneity and statistical distribution of elastic and plastic properties across the population of mechanical components (grains and grain boundaries) in the material. Greater degrees of heterogeneity lead to more intense stress concentrations across a less dense pattern. Lower degrees of elastic heterogeneity lead to a denser pattern of stress transmission that carries smaller modulations. Paralleling the development of shear bands in granular materials, the stress patterns lead directly to shear localization. The proposed project will compare the stress and strain heterogeneity observed in experimentally deformed mono-phase rocks with the stress and strain heterogeneity observed in FE models tuned to simulate these rocks. Specifically, the variation in the orientation of local stress tensor as predicted by FE models will be compared with microstructures that are sensitive to the compression direction such as twins and kinkbands and the distribution of the magnitude of the local compressive stress predicted by the FE models will be compared with local compressive stress distributions derived from synchrotron x-ray diffraction data from in-situ deformation experiments. Model design elements to be examined include the shapes of grains, grain boundary and grain interior rheology, as well as model size and aspect ratio. The impact of using 2D vs 3D models will also be examined. Additional direct comparisons will be made between the pattern of variation in microstrains observed on the surface of experimentally deformed polycrystalline slabs and the results from FE models built to match EBSD maps of the slab surfaces. These comparisons between models and experimental data will provide a test of the stress percolation hypothesis and provide a foundation for further investigations of stress percolation.

该项目将测试应力渗透假说及其用于使用地质材料的实用性。 科学家和工程师都认为，当岩石由构造力量或工程项目的背景下，岩石在整个岩石中均匀地持有。 PI提出了一个替代假设，即，岩石上外部载荷产生的应力是根据类似于流经原本干砂的水产生的模式的模式。 如果该假设证明是正确的，那么岩石中的应力分布将与表现出“渗透”行为的大量现象，包括在颗粒材料中观察到的应力分布模式。 因此，该假设的一个含义是，有一个单一的统一物理模型来变形所有地球材料。理解岩石中应力分布的价值是，它将使我们能够创建更好的岩石变形模型，并更好地预测岩石的机械行为，这对我们加深了我们对各种地球过程的理解以及工程应用的影响。 压力渗透的存在以及对岩石中其运作方式的精致理解对除地球物理以外的许多学科具有巨大的影响。 材料科学，冶金和冲击物理学的研究人员都在与所谓的“多晶问题”中挣扎 - 像岩石一样，许多固体材料由具有多种特性的结晶晶粒骨料组成。 了解许多这些材料对加载的反应已经提出了与从事岩石变形的人相似的挑战。 因此，这项研究将有助于更好地理解所有这些学科的机械问题。使用PI的有限元（FEM）模拟PI最近表明，应力和应变的局部变化参与了大规模模式，这可能是由应力渗透引起的。这些模式是材料中机械组件（晶粒和晶界）群体中弹性和塑性特性的异质性和统计分布的函数。 较高程度的异质性导致越来越密集的胁迫浓度更加强烈。 较低的弹性异质性导致应力传播的较密集的模式，该模式带来了较小的调制。 应力模式与颗粒材料中的剪切带的发展平行，直接导致剪切定位。 该提出的项目将比较在实验变形的单相岩石中观察到的应力和应变异质性与在调谐以模拟这些岩石的FE模型中观察到的应力和应变异质性。 具体而言，Fe模型预测的局部应力张量的方向的变化将与对压缩方向敏感的微观结构进行比较，例如双胞胎和扭结频带以及Fe模型预测的局部压缩应力的大小的分布将与来自SynchRotron X量X型乘以从SynCheration In-Sytecation In-Sytecation Inscation Incitation Incoration Insitumation synchrotron x-ray fraction Incoration syeration Furemations相比。要检查的模型设计元素包括谷物，晶界和晶粒内部流变学的形状，以及模型大小和纵横比。也将检查使用2D与3D模型的影响。将在实验变形的多晶平板表面观察到的微构株的变化模式与构建的Fe模型的结果之间进行其他直接比较，以匹配平板表面的EBSD图。模型和实验数据之间的这些比较将提供应力渗透假设的测试，并为进一步研究应力渗透提供了基础。