Creep Deformation in Shale at Submicron Scale

页岩是一种细粒沉积岩，由粘土、石英、长石、黄铁矿、碳酸盐和有机物质的混合物组成，形成了一种高度非均质的纳米复合材料。作为一种密封岩石，页岩被用来在地下储存有毒的、长寿命的化学和放射性废物。事实上，由于页岩的抗破裂能力，结晶岩和厚页岩序列长期以来一直被认为是主要的储存地点。页岩的力学性质取决于其基本成分的性质，包括粘土颗粒和有机包裹体的性质，以及混合物的孔隙度。在很大程度上，由于其粘土和有机物含量，页岩表现出显著的蠕变变形，这可能会在区域范围内造成沉降问题，并改变其作为有毒废物密封的有效性，这些有毒废物必须被密封数千年。该奖项支持在纳米尺度上研究页岩蠕变变形行为的基础研究。对这种非均质材料的力学性能的研究提供了对其作为密封功能至关重要的尺度上控制蠕变的基本过程的见解，并允许在更大尺度上解释蠕变现象。这项研究涉及多个学科，包括材料科学、生物力学和其他与纳米多孔材料研究有关的科学学科。它支持一名女博士生，这将有助于扩大代表性不足的群体和本科生的参与。该项目采用实验室测试和数值模拟相结合的方法，研究了页岩在纳米尺度下的蠕变特性。实验包括纳米压痕测试，以确定页岩组分的基本力学特性，以及使用全场透射x射线显微镜（TXM）进行纳米级分辨率的孔隙结构成像，TXM是SLAC国家加速器实验室斯坦福同步辐射光源的稀缺资源。数值模拟包括一种新的混合理论公式，用于软物质和硬物质的固体-固体混合，反映了亚微米尺度上页岩非均质结构的真实物理表征。这两种物质具有截然不同的刚度和蠕变特性，它们之间的相互作用可能会揭示微裂纹在非均质纳米复合材料中形成和传播的本质。从建模的角度来看，混合理论首次用于描述纳米尺度上软物质和硬物质的固体-固体混合物。

Shale is a fine-grained sedimentary rock consisting of a mixture of clay, quartz, feldspar, pyrite, carbonate, and organic materials forming a highly heterogeneous nanocomposite. As a seal rock, shale has been used to contain toxic, long-lived chemical and radioactive waste products in the ground. In fact, crystalline rocks and thick shale sequences have long been considered as prime storage sites because of the shale's ability to resist fracture. The mechanical properties of shale depend on the properties of its basic constituents, including those of clay particles and organic inclusions, as well as the porosity of the mixture. Due in large part to its clay and organic content, shale exhibits significant creep deformation that can create subsidence issues on a regional scale, as well as alter its effectiveness as a seal for toxic waste products that must be contained for thousands of years. This award supports fundamental research to investigate the creep deformation behavior of shale at the nanometer scale. Investigation into the mechanical properties of this heterogeneous material provides insight into the fundamental processes governing creep at a scale critical for its function as a seal, as well as allows interpretation of the creep phenomena at larger scales. The research involves several disciplines including materials science, biomechanics, and other scientific disciplines concerned with the studies of nanoporous materials. It supports a female doctoral student who will help broaden the participation of underrepresented groups and undergraduate students.The project investigates the creep properties of shale at nanometer scale using a combination of laboratory testing and numerical modeling. Experiments include nanoindentation testing to determine basic mechanical properties of the shale constituents, and imaging of the pore structure with nanometer-scale resolution using full-field Transmission X-Ray Microscopy (TXM), a scarce resource available at the Stanford Synchrotron Radiation Lightsource within the SLAC National Accelerator Laboratory. Numerical modeling includes a novel formulation of mixture theory for solid-solid mixture of softer matter and harder matter, reflecting a realistic physical representation of the heterogeneous structure of shale at submicron scale. Interaction between these two matters, which possess starkly different stiffness and creep properties, could potentially shed light onto the nature by which micro-cracks form and propagate through a heterogeneous nanocomposite. From a modeling standpoint, mixture theory is used for the first time to delineate a solid-solid mixture of softer matter and harder matter at the nanometer scale.