Stress Corrosion Micro-Cracking or Static Fatigue: The Principal Cause of Rate Effects and "Aging" in Sand

砂土的时间和速率效应影响土结构的短期和长期行为，但对这种行为的原因缺乏了解。 提出了一个假设，利用颗粒表面微观形态特征的微破裂过程来解释砂中时间效应的性质。 这项研究所采用的新方法使其具有潜在的变革性。 实验观察技术的基础上扫描电子显微镜和原子力显微镜将被用来产生视觉证据的时间延迟微破裂的凹凸不平的晶粒表面（静态疲劳），而微观和宏观加载测试将被用来获得定量证据。 这项研究的科学价值在于其创造性和原创性的概念，利用多尺度方法来解释沙子中令人困惑的时间相关效应。 本研究的工程相关性在于，土壤的时间依赖性行为可能对土结构的设计和长期行为以及土壤-结构相互作用产生重要影响（例如，由于沙子行为的时间依赖性，挡土结构上的荷载可能会随着时间的推移而增加）。 这项研究的影响将影响岩土工程以外的领域，例如，空间探索任务，这需要预测表面的流动性，计划钻井作业，以及处理月球/火星的风化层。 由于缺乏水和大气，月壤颗粒具有丰富的表面形态，这是本研究假设的核心特征。 这项研究促进了一个新的概念，推进发现，并促进学习。

Time and rate effects in sands affect both the short- and long-term behavior of earth structures, yet understanding of the causes of that behavior is lacking. A hypothesis is suggested that makes use of the process of micro-fracturing of the microscopic morphological features on grain surfaces to explain the nature of time effects in sand. The new approach this research is taking makes it potentially transformative. Experimental observation techniques based on Scanning Electron Microscopy and Atomic Force Microscopy will be employed to produce visual evidence for time-delayed micro-fracturing of asperities on grain surfaces (static fatigue), whereas micro- and macro-loading tests will be used to gain quantitative evidence. The scientific merit of this research is in its creative and original concept exploiting the multi-scale approach to explain the puzzling time-related effects in sand. The engineering relevance of this research is that the time-dependent behavior of soils can have important consequences on design and long-term behavior of earth structures and on soil-structure interaction (for instance, the load on retaining structures can increase in time as a result of the time-dependent nature of sand behavior). The impact of this research will affect areas beyond geotechnical engineering, e.g., space exploration missions, which require predictions of surface mobility, planning of drilling operations, and processing of the Lunar/Martian regolith. Due to the absence of water and atmosphere, Lunar regolith grains have a rich surface morphology, a characteristic central to the hypothesis in this research. This research promotes a new concept, advances discovery, and promotes learning.