EAGER: Developing an Experimental Technique for Measuring Very Slow Crack Velocities in Rock Using the Atomic Force Microscope

亚临界裂纹扩展是岩石随时间退化和破坏的主要机制之一。尽管在岩石亚临界裂纹扩展方面已经进行了大量的工作，但仍然存在一些非常重要的问题。双扭转试验和其他常规的亚临界裂纹扩展测试技术测量的裂纹速度在10-8到10-3m/S之间，在这个范围内，对于很低的裂纹速度，不可能确定裂纹速度-KI曲线的形状，而这是准确预测低应力下地质结构长期行为所必需的。此外，关于岩石中剪切裂纹扩展的起源也存在争议，这是传统显微镜无法充分解决的问题。为了解决这些问题，将开发基于原子力显微镜(AFM)的实验技术。原子力显微镜测量裂纹扩展的分辨率不到4纳米，这使得可以测量到小到10-13m/S的裂纹速度。这将为裂缝速度-KI曲线的形状和岩石的亚临界截止点提供基本信息。开发的实验程序将包括对小岩石样品进行周期性的机械加载，以产生非常少量的裂纹扩展，然后进行AFM研究，以测量裂纹扩展的数量和模式。为玻璃中I型裂纹扩展开发的实验室和AFM技术将首先用于岩石样品，并将进行修改，以考虑到复杂的岩石微结构，并研究拉伸和剪切裂纹的扩展。这项研究将提高我们预测关键地质结构长期稳定性的能力，如坝基、隧道、地下核废料储存设施、地下二氧化碳封存设施、公路斜坡和许多其他结构。此外，研究结果还可能影响其他对环境辅助裂纹扩展和破坏感兴趣的科学和工程领域，如材料科学、断裂力学、采矿和土木与机械工程。通过国际出版物和远程课程传播这项研究的结果，这项研究将成为全世界本科生和研究生培训的一部分。

Subcritical crack growth is one of the dominant mechanisms for time-dependent rock degradation and failure. In spite of the substantial amount of work that has been conducted on subcritical crack growth in rocks, some very important issues still remain. The double torsion test and other conventional techniques for subcritical crack growth testing measure crack velocities between 10-8 and 10-3 m/s. Within this range, it is not possible to determine the shape of the crack velocity vs. KI curve for very low crack velocities, which is needed in order to accurately predict the long term behavior of geologic structures subjected to low stresses. Also, there is controversy about the origin of shear crack growth in rocks that cannot be adequately resolved with traditional microscopy. To address these issues, experimental techniques based the Atomic Force Microscope (AFM) will be developed. The resolution of the AFM for crack growth measurements is less than 4 nanometers, which allow crack velocities as small as 10-13 m/s to be measured. This will provide fundamental information on the shape of the crack velocity vs. KI curve and the subcritical cutoff for rocks. The experimental procedure developed will involve periodic mechanical loading of small rock samples to create very small amounts of crack growth, followed by AFM investigations to measure the amount and pattern of crack growth. Laboratory and AFM techniques developed for mode I crack growth in glass will initially be used for the rock specimens, and modifications will be made to account for the complex rock microstructure and also to investigate both tensile and shear crack growth. The research will increase our ability to predict the long-term stability of critical geologic structures such as dam foundations, tunnels, underground nuclear waste storage facilities, underground CO2 sequestration sties, highway slopes, and many other structures. Also, the results could impact other science and engineering fields that are interested in environmentally assisted crack growth and failure, such as material science, fracture mechanics, mining, and civil and mechanical engineering. By disseminating the results of this research through international publications and distance courses, this research will be part of the training for undergraduate and graduate students worldwide.