Collaborative Research: Three-Dimensional Assessment of Stresses and Fracture Behavior in Sand

合作研究：砂中应力和断裂行为的三维评估

• 批准号: 1361267
• 负责人: Richard Regueiro
• 金额: $ 7.06万
• 依托单位: University of Colorado at Boulder
• 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: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1361267&HistoricalAwards=false
• 关键词: Collaborative; Research; Three; Dimensional; Assessment

This award concerns fundamental aspects of stress distribution and fracture behavior in sands. Granular materials such as sand, gravel, aggregates, agricultural grains, and pharmaceutical products are comprised of discrete particles in contact with each other. At the micro-scale, each particle is in contact with neighboring particles where individual particle properties and contact mechanics govern particle interaction. At the macro-scale, multiple-particle assemblies interact through networks of force chains at contact points. As the applied stresses increase, some particles may fracture, which causes a change in the distribution of force chains within the mass of the granular material. Characterization of force chains has been the subject of extensive research primarily using photoelastic materials and the discrete element method (DEM). Experimental characterization, however, of the development and evolution of force chains in three dimensions (3D) is not available. Measuring properties of force chains and contact forces between particles experimentally - while they may be fracturing - is an important step toward enhancing knowledge of particle-scale behavior in granular materials. The award supports fundamental research to provide critical experimental measurements at a range of length-scales, from the particle-scale to the size of a typical soil mechanics laboratory specimen. The research will have major impact on the development of more accurate computational models that can be applied to better understand a variety of engineering problems involving flow and deformation of granular materials, insertion of piles in sandy soils, in-situ measurement of shear strength in sands using penetrometer devices, tires rolling or skidding through granular soils on the Earth or other planets, high velocity impact of sands, explosive loading of soils, grain silo design, and more efficient manufacturing, handling, and processing of pharmaceutical, agricultural, and food products that are granular in nature.The objective of the research is to use 3D x-ray diffraction (3DXRD) and synchrotron micro-computed tomography (SMT) to answer fundamental questions about fracture behavior, contact stresses and strains, and onset and evolution of force chains in silica sand. The research will (i) investigate the influence of crystallographic orientation on fracture behavior of silica sand; (ii) measure the distribution of strain and stress within compressed sand particles and investigate their influence on particle fracture in 3D; (iii) quantify the contact stresses between sand particles and assess their influence on fracture behavior of silica sand and on the evolution of force chains; (iv) investigate the factors that affect the onset and collapse of force chains in sand in 3D; and (v) model fracture behavior and force transmission behavior of silica sand in 3D using crystal elasticity and the finite element method (FEM). SMT and 3DXRD are powerful non-destructive 3D techniques that offer complementary experimental measurements and have the potential to yield breakthroughs in the measurement of stress and strain in granular materials at multiple length-scales.

该奖项涉及砂中应力分布和断裂行为的基本方面。 粒状材料如沙子、砾石、骨料、农业谷物和药品由彼此接触的离散颗粒组成。 在微观尺度上，每个颗粒与相邻颗粒接触，其中单个颗粒特性和接触力学控制颗粒相互作用。 在宏观尺度上，多粒子集合体通过接触点处的力链网络相互作用。 随着所施加的应力增加，一些颗粒可能断裂，这导致颗粒材料质量内的力链分布的变化。 力链的表征一直是广泛研究的主题，主要使用光弹性材料和离散元法（DEM）。 然而，在三维（3D）的力链的发展和演变的实验表征是不可用的。 通过实验测量力链的性质和颗粒之间的接触力-虽然它们可能会破裂-是朝着增强颗粒材料中颗粒尺度行为的知识迈出的重要一步。 该奖项支持基础研究，以提供从颗粒尺度到典型土壤力学实验室样本大小的一系列长度尺度的关键实验测量。 这项研究将对开发更精确的计算模型产生重大影响，这些模型可用于更好地了解各种工程问题，包括颗粒材料的流动和变形，桑迪中桩的插入，使用重力仪设备原位测量砂土中的剪切强度，轮胎在地球或其他行星上滚动或滑动通过颗粒土，沙子的高速冲击，土壤的爆炸加载，粮食筒仓设计，以及更有效地制造，处理和加工药物，农业和食品的颗粒状产品。研究的目的是使用3D X射线衍射（3DXRD）和同步加速器微计算机断层扫描（SMT）来回答有关断裂行为，接触应力和应变的基本问题，以及硅砂中力链的发生和演化。研究内容包括：（i）石英砂晶体取向对石英砂断裂行为的影响;（ii）测量压缩砂粒内部的应变和应力分布，并研究其对颗粒三维断裂的影响;（iii）量化砂粒之间的接触应力，并评估其对石英砂断裂行为和力链演化的影响;（iv）研究影响3D中砂中力链的开始和崩溃的因素;以及（v）使用晶体弹性和有限元法（FEM）在3D中模拟硅砂的断裂行为和力传递行为。SMT和3DXRD是强大的非破坏性3D技术，可提供互补的实验测量，并有可能在多个长度尺度下测量颗粒材料的应力和应变方面取得突破。