Experimental and Theoretical Investigation of Deformation in Granular Materials: A Micromechanics Approach

颗粒材料变形的实验和理论研究：微观力学方法

• 批准号: 0010124
• 负责人: Balasingam Muhunthan
• 金额: $ 28.82万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-03-15 至 2006-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0010124&HistoricalAwards=false
• 关键词: Experimental; Theoretical; Investigation; Deformation; Granular

The deformation of soils in the field and laboratory are commonly observed to concentrate into shear bands formed during strain localization. While this mechanism is widely appreciated by engineers and researchers, it remains difficult to model, predict and analyze. The main difficulty can be attributed to the fact that while classical continuum mechanics models that do not include microstructure length scales can predict the onset of instability, they cannot predict the size and evolution of the shear bands. In particular, the classical theories of plasticity break down in the post-bifurcation regime. The main objective of this study is to develop a microstructure based continuum model to study deformation and localization in granular materials. The model is based on crystal plasticity but includes two microstructure length scales; one associated with the plastic curvature (orientation re-distribution) and the other related to the porosity re-distribution, both of which can be directly quantified by experiments. The study is unique in that the microstructure model parameters are determined directly from measurements. Granular specimens are hardened by impregnation with resin and their microstructure captured by means of non-invasive x-ray computer tomography. Evolution of the microstructure model parameters is monitored at various stages of shear deformation. The model will be implemented into a 3-D finite element code and used to identify deformation patterning, softening, and instabilities (shear banding and liquefaction) in boundary value problems.The experimental and analytical program will lead to a better understanding of the phenomenon of bifurcation and localization and to analytical methods for analyzing strain localization not only in laboratory specimens, but also in practical boundary value problems in geotechnical engineering. The outcome of this work would also have implications to the modeling of other type of materials such as metals and composites that exhibit deformation instabilities and shear banding.

在现场和实验室中，通常观察到土壤的变形集中在应变局部化过程中形成的剪切带中。 尽管这种机制得到了工程师和研究人员的广泛认可，但它仍然难以建模、预测和分析。主要困难可归因于这样一个事实：虽然不包括微观结构长度尺度的经典连续介质力学模型可以预测不稳定的开始，但它们无法预测剪切带的大小和演化。 特别是，经典的可塑性理论在分岔后的状态下崩溃了。本研究的主要目标是开发基于微观结构的连续体模型来研究颗粒材料的变形和局部化。该模型基于晶体塑性，但包括两个微观结构长度尺度；一个与塑性曲率（取向重新分布）相关，另一个与孔隙率重新分布相关，两者都可以通过实验直接量化。该研究的独特之处在于微观结构模型参数是直接根据测量确定的。 颗粒状样品通过树脂浸渍而硬化，并通过非侵入性 X 射线计算机断层扫描捕获其微观结构。 在剪切变形的各个阶段监测微观结构模型参数的演变。 该模型将被应用到 3-D 有限元代码中，并用于识别边值问题中的变形模式、软化和不稳定性（剪切带和液化）。实验和分析程序将有助于更好地理解分叉和局部化现象，并形成不仅在实验室样本中而且在岩土工程中实际边值问题中分析应变局部化的分析方法。 这项工作的结果也将对其他类型材料的建模产生影响，例如表现出变形不稳定性和剪切带的金属和复合材料。