Experimental Investigation of Deep Penetration in Sand

本项目探讨了砂土深层穿透问题的基本原理。深贯问题几乎包含了地质力学家可能面临的所有挑战：大位移、大旋转、大应变、应变局部化、破碎和移动的土-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，包括射弹穿透地面，桩基础设计和锥形穿透测试的解释，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，例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，对国防工业至关重要的应用（弹丸穿透）的更好理解，可用于教育和研究的图像数据库的生产，以及先进技术和计算机模拟研究人员的培训。该研究具体采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破碎砂中的锥突。一个独特的半圆柱形腔室，有一个平坦的有机玻璃壁，可以观察半圆穿透仪的垂直运动，将使用最先进的高分辨率数码相机和显微镜来获取不同条件下穿透过程的图像。图像将通过两种方式进行处理：使用DIC获得土壤中的位移场和应变场，以及使用算法从其图像中产生土壤的粒度分布。侵彻阻力、局部应力、位移和应变场数据集可以看作是侵彻边值问题的实验解。将在整个侵彻过程中评估粒度级配，从而使研究团队能够考虑发生破碎的地方的侵彻阻力与位移场和应变场之间的关系。校正室测试由一个完整的实验室测试程序补充，以产生可用于验证理论模拟和开发分析和设计方法的数据。高质量的实验数据将包括在独特的霍普金森棒中进行的测试数据，该棒专门设计用于测试单轴或三轴条件下的土壤。还将开展工作，以提高使用物质点法的穿透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.