纳米级粘土中裂纹的MD模拟
MD modeling of cracks in clay at the nanoscale
摘要：
粘土中的裂缝在岩土工程和地质环境工程中是重要的（例如，路堤侵蚀和填埋场覆盖系统的稳定性）。本文通过全尺度分子动力学模拟研究了纳米尺度下粘土中裂纹的成核和扩展机理。所采用的粘土为叶蜡石，力场为CLAYFF。本文研究了叶蜡石粘土层在单轴拉伸和单剪作用下裂纹的形成。数值结果表明，叶蜡石纳米粘土层中的裂纹是脆性的和应变率相关的。小的应变速率导致低的极限拉伸/剪切强度。随着应变速率的增加，粘土裂纹由单裂纹向多裂纹扩展。从原子尺度上的键断裂分析探讨了裂纹的形成机理。结果表明，第一个键断裂发生在硅-表面氧键中。当裂纹扩展时，与其他类型的金属-氧相互作用相比，断裂的硅-表面氧键的相对百分比是最小的，这表明硅和表面氧原子之间的原子相互作用是最强的。为了理解裂纹的扩展，我们还研究了叶蜡石的应力强度因子和能量释放率及其在原子尺度上的尺寸依赖性。
英文摘要：
Cracks in clay are significant in geotechnical and geoenvironmental engineering (e.g., embankment erosion and stability of landfill cover systems). This article studies the mechanism of nucleation and growth of cracks in clay at the nanoscale through full-scale molecular dynamics simulations. The clay adopted is pyrophyllite, and the force field is CLAYFF. The crack formation in a pyrophyllite clay layer is evaluated under uniaxial tension and simple shear. The numerical results show that cracks in the nanoscale pyrophyllite clay layer are brittle and strain-rate dependent. Small strain rate results in low ultimate tensile/shear strength. As strain rate increases, clay crack shifts from a single-crack pattern to a multiple-crack one. The cracking mechanism is investigated from bond breakage analysis at the atomic scale. It is found that the first bond breakage occurs in the silicon-surface oxygen bond. As a crack propagates, the relative percentage of broken silicon-surface oxygen bonds is the smallest compared to other types of metal-oxygen interactions, demonstrating that the atomic interaction between silicon and surface oxygen atoms is the strongest. To understand the propagation of cracks, we also study the stress intensity factor and energy release rate of pyrophyllite and their size dependence at the atomic scale.
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