Enhancement of Experimental Imaging Capabilities for Advanced Study of Shear Band Growth and Evolution

增强实验成像能力以促进剪切带生长和演化的高级研究

• 批准号: 0220309
• 负责人: Amy Rechenmacher
• 金额: $ 7.47万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-07-01 至 2004-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0220309&HistoricalAwards=false
• 关键词: Enhancement; Experimental; Imaging; Capabilities; Advanced

CMS-0220309PI: Amy RechenmacherInstitution: Johns Hopkins UniversityTitle: "Enhancement of Experimental Imaging Capabilities for Advanced Study of Shear Band Growth and Evolution"Abstract:An experimental investigation is currently underway, involving plane strain testing and digital image analysis of shear bands. The objective is to comprehensively evaluate the nature of the relationship between deposition void ratio and critical state line (CSL) for sands. The study has been motivated by results of recent research in which experimental quantification of localized deformations (shear bands), and thus critical states, in dilative sands has indicated that CSL position in void ratio-effective stress space may not be unique, but rather dependent on deposition void ratio. Since critical state concepts and the CSL are widely used in geotechnical analysis and design, the impact of these findings is potentially significant. The ultimate goal is to derive from the results a quantitative description of the relationship between deposition void ratio and CSL, and to develop recommendations for incorporating the findings into current analysis procedures for liquefaction potential and constitutive models that utilize the CSL in its current unique form.Experiments are being conducted in an advanced plane strain testing apparatus. The apparatus is configured to promote unconstrained formation of shear bands and to permit the localization process to be analyzed photographically. The technique of Digital Image Correlation (DIC) is used to measure directly localized displacements in sand specimens to a high level of accuracy. The incorporation of a higher resolution digital camera than in previous studies, combined with the synchronization of image acquisition with data acquisition and control, will enable more accurate quantification of shear band deformations, including displacement patterns associated with shear band formation. The highly developed photographic capabilities also will enable quantitative study of deformation mechanisms associated with other localized displacement phenomenon, such as temporary shear bands.The configuration of the biaxial testing apparatus as described above offers one of the only currently available experimental methods to quantify the evolution of localized displacements in soils. Unfortunately, however, in its current configuration only one plane of the shear band is visualized, yielding question as to the validity of the displacement quantification, in spite of its high accuracy. In addition, the potential occurrence of out-of-plane volumetric exchange within the shear band cannot be addressed.This study aims to overcome the stated limitations of the current experimental system by incorporating modifications to allow imaging through both plane strain walls, while keeping in tact the out-of-plane force measurement capabilities. The modifications consist of the addition of a second digital camera, and load wall redesign to accommodate imaging. These modifications shall affect several system improvements. First, quantification of local displacements on two planes through the depth of the shear band will enable confirmation of locally derived critical state void ratios. Second, the real-time comparison among displacement fields at both ends of the shear band and transducer measurements currently available at midpoint of the specimen depth will provide the opportunity to make more reliable observations about deformation uniformity through the depth of the shear band. Measurements of local deformations to such a level of detail should contribute significantly to the understanding of granular soil behavior.

CMS-0220309 PI：Amy Rechenmacher机构：约翰霍普金斯大学标题：“增强剪切带生长和演化高级研究的实验成像能力“摘要：目前正在进行一项实验研究，涉及剪切带的平面应变测试和数字图像分析。 目的是综合评价砂的沉积孔隙比与临界州线（CSL）之间关系的性质。 这项研究的动机是最近的研究结果，其中实验量化的局部变形（剪切带），从而临界状态，在膨胀砂已表明，CSL的位置在空隙比有效应力空间可能不是唯一的，而是依赖于沉积空隙比。 由于临界状态的概念和CSL被广泛用于岩土工程分析和设计，这些研究结果的影响是潜在的显着。 最终的目标是从结果中得出沉积孔隙比和CSL之间的关系的定量描述，并制定建议，将调查结果纳入当前的液化潜力和本构模型，利用CSL在其目前独特的形式分析程序。实验正在进行一个先进的平面应变测试装置。 该装置被配置为促进剪切带的不受约束的形成，并允许对定位过程进行化学分析。 数字图像相关（DIC）技术被用来直接测量局部位移的砂样，以高精度的水平。 与以前的研究相比，结合更高分辨率的数码相机，图像采集与数据采集和控制的同步，将能够更准确地量化剪切带变形，包括与剪切带形成相关的位移模式。 高度发达的摄影能力也将使定量研究与其他局部位移现象，如临时剪切带相关的变形机制，双轴测试设备的配置如上所述提供了目前唯一可用的实验方法之一，以量化在土壤中的局部位移的演变。 然而，不幸的是，在其目前的配置中，只有一个平面的剪切带是可视化的，产生的问题，位移量化的有效性，尽管它的高精度。 此外，剪切带内的平面外体积交换的潜在发生无法解决。这项研究的目的是克服现有实验系统的局限性，通过合并修改，使成像通过两个平面应变壁，同时保持在机智的平面外力测量能力。 修改包括增加第二个数码相机，并重新设计负载墙以适应成像。 这些修改将影响几个系统的改进。 首先，通过剪切带深度的两个平面上的局部位移的量化将能够确认局部导出的临界状态空隙比。 其次，在剪切带两端的位移场和传感器测量值之间的实时比较目前可在试样深度的中点将提供机会，使更可靠的观察变形均匀性通过剪切带的深度。 局部变形的测量，这样的细节水平，应有助于显着理解粒状土的行为。