Experimental Investigation of Deep Penetration in Sand

这个项目研究了在沙子中深层渗透问题的基本原理。深部贯入问题实际上包含了地质机械师可能面临的所有挑战：大位移、大转动、大应变、应变局部化、破碎和移动的土壤-金属边界。因此，这项研究的影响是双重的：它将促进对应用于不同领域的问题的理解，包括弹丸侵入地面、桩基设计和圆锥贯入测试的解释，但它也将有助于促进对颗粒(颗粒)介质中发生的基本过程的理解，如应变局部化和颗粒破碎，以及如何在计算模拟中处理所有这些复杂过程。因此，对社会的好处是多方面的，包括颗粒介质科学的普遍进步，基础设计的经济性，对国防工业至关重要的应用(弹丸渗透)的更好理解，可用于教育和研究的图像数据库的产生，以及先进技术和计算机模拟方面的研究人员培训。这项研究特别使用校准室测试和数字图像相关(DIC)技术的强大组合来研究可压碎沙中的锥体渗透。一个独特的半圆柱形洞室，带有平坦的有机玻璃墙壁，可以观察半圆形贯入仪的垂直运动，将用最先进的高分辨率数码相机和显微镜采集各种条件下的贯入过程的图像。这些图像将以两种方式进行处理：使用DIC获得土壤中的位移场和应变场，以及根据土壤图像生成土壤颗粒分布的算法。侵彻阻力、局部应力、位移场和应变场数据集可视为侵彻边值问题的实验解。粒度分级将在整个渗透过程中进行评估，从而使研究团队能够考虑在任何地方发生的粉碎、渗透阻力与位移场和应变场之间的关系。校准室测试由完整的实验室测试程序补充，以产生数据，这些数据可用于理论模拟的验证和分析和设计方法的开发。高质量的实验数据将包括来自一种独特的霍普金森杆的测试数据，该杆专门设计用于在单轴或三轴条件下测试土壤。还将开展工作，利用材料点法提高侵彻问题的计算模拟能力。

This project examines the fundamentals of the problem of deep penetration in sand. The deep penetration problem contains virtually all the challenges that geomechanicians may face: large displacements, large rotations, large strains, strain localization, crushing, and a moving soil-metal boundary. The impact of the research therefore is dual: it will advance the understanding of a problem with applications to diverse fields, including projectile penetration into the ground, design of pile foundations and interpretation of the cone penetration test, but it will also help advance the understanding of fundamental processes that happen in granular (particulate) media, such as strain localization and particle crushing and how all of these complex processes should be handled in computational simulations. Benefits for society therefore are multiple, including the general advancement of the science of granular media, economies in foundation design, a better understanding of an application (projectile penetration) that is vital to the defense industry, the production of a database of images that can be used in education and research, and the training of researchers in advanced technology and computer simulations.The research specifically uses the powerful combination of calibration chamber testing and the digital image correlation (DIC) technique to study cone penetration in crushable sands. A unique half-cylindrical chamber with a flat Plexiglass wall that allows observation of the vertical motion of half-circular penetrometers will be used to acquire images of the penetration process under various conditions with state-of-the-art high-resolution digital cameras and microscopes. The images will be processed in two ways: using DIC to obtain the displacement and strain fields in the soil and an algorithm that produces the particle size distribution of the soil from an image of it. The penetration resistance, local stresses, and the displacement and strain field dataset may be viewed as an experimental solution to the penetration boundary-value problem. Particle size gradation will be assessed during the entire penetration process, thereby enabling the research team to consider the relationship between crushing, wherever it occurs, penetration resistance and the displacement and strain fields. The calibration chamber tests are complemented by a complete laboratory testing program to produce data that can later be used in validation of theoretical simulations and development of methods of analysis and design. The high-quality experimental data will include data from tests in a unique Hopkinson bar especially designed to test soil under uniaxial or triaxial conditions. Work will also be done to advance computational simulation capabilities of penetration problems using the material point method.