The Role of Fabric on the Behavior of Granular Materials Subjected to Cyclic Loading

预测颗粒材料的循环行为仍然是一个主要的工程挑战，在过去的几十年里，现有的计算机模型还没有充分捕捉。粒状材料的循环行为在许多应用中至关重要，包括地震荷载下的土壤行为和海上清洁能源采集。当前模型中缺少的一个环节是包含内部颗粒结构（织物），已知其控制颗粒材料的整体行为，特别是在材料经历负载反转的循环负载下。本研究的目的是通过仔细研究织物的影响来扩展计算机模型对循环荷载下颗粒材料的预测能力。这项研究将使用先进的计算，实验和原位技术，以开发下一代模型的粒状材料，如沙子。这项研究是加州理工学院和挪威岩土工程研究所之间的合作。此外，该项目将有助于培训本科生和研究生。本科生将通过加州理工学院的夏季本科生研究奖学金参与其中。这项研究也将继续扩大岩土工程的国际教育基础设施，特别是美国和欧洲之间的重大影响。这项研究的工作假设是，连续体行为编码的规模，相邻的颗粒相互作用。这些相互作用建立了一个应力路径网络或结构，动态适应不断变化的载荷条件;产生了细观尺度特征，如力链，这是颗粒材料所独有的。其结果是，织物的演变引起连续变化的中尺度和连续响应的材料。缺乏能够准确预测颗粒材料循环行为的连续介质模型可能是由于普遍缺乏对织物如何随循环载荷而演变以及它如何影响颗粒材料行为的了解。本研究旨在填补这一空白，完成三个中心的研究任务：1：表征和重建的固有组构; 2：模拟组构演化的循环应力路径; 3：连续描述和验证组构演化关系。这项研究将激励新的实验装置的设计，并激发新一代的颗粒材料预测本构模型。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Predicting the cyclic behavior of granular materials remains a major engineering challenge that is not yet sufficiently captured by existing computer models developed in the last few decades. Cyclic behavior of granular materials is critical in a large number of applications, including soil behavior under earthquake loading and clean energy harvesting offshore. A missing link in the current models is the inclusion of internal granular structure (fabric), which is known to control the overall behavior in granular materials, especially under cyclic loads where the material experiences load reversals. The objective of this research is to extend the predictive capability of computer models for granular materials subjected to cyclic loading by carefully investigating the effects of the fabric. This research will use cutting edge computational, experimental and in situ techniques to develop next-generation models for granular materials such as sands. This research is a collaboration between Caltech and the Norwegian Geotechnical Institute. Furthermore, this project will contribute to the training of students at the undergraduate and graduate levels. Undergraduate students will be involved via the summer undergraduate research fellowship at Caltech. This research will also have significant impact on continuing to expand the international educational infrastructure in geotechnical engineering, especially between the United States and Europe.The working hypothesis of this research is that continuum behavior is encoded at the scale where neighboring grains interact. These interactions establish a stress path network, or fabric, that adapts dynamically to changing loading conditions; giving rise to meso-scale features like force chains, which are unique to granular materials. The upshot of this is that the evolution of fabric induces continuous change in the meso-scale and the continuum response of the material. The dearth of continuum models capable of predicting accurately the cyclic behavior of granular materials could be attributed to a general lack of understanding of how fabric evolves as a function of cyclic loading and how it influences the granular material behavior. This research aims to fill this gap by accomplishing three central research tasks: 1: Characterization and reconstitution of inherent fabric; 2: Modeling fabric evolution in cyclic stress paths; 3: Continuum description and validation of fabric evolution relations. This research will motivate the design of new experimental apparatuses and inspire a new generation of predictive constitutive models for granular materials.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.