Nanoscale crack propagation in clay with water adsorption through reactive MD modeling
Nanoscale crack propagation in clay with water adsorption through reactive MD modeling
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DOI：
10.1002/nag.3507
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发表时间：
2022-09
影响因子：
4
通讯作者：
Zhe Zhang;Xiaoyu Song
中科院分区：
文献类型：
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作者：
Zhe Zhang;Xiaoyu Song
粘土是纳米材料，原子尺度的开裂机理对于揭示粘土在连续介质尺度上的开裂机理至关重要。在本文中，我们利用键序力场的反应分子动力学（MD）研究了叶叶石和钙蒙脱土中ⅰ型和ⅱ型裂纹的扩展机制。粘土水吸附是通过在粘土表面加入水分子来考虑的。在平衡阶段，水的吸附会引起预定边缘裂纹区域的弯曲变形。水分子相对较小的取向角表明裂纹扩展过程中形成了氢键。吸附水的峰数密度随菌株的增加而减小。分析了裂纹尖端在载荷作用下的原子结构演化，以解释纳米尺度裂纹扩展机制。数值结果表明，裂纹尖端首先钝化，裂纹尖端曲率半径显著增大，裂纹长度变化不大；通过对I型和II型裂纹中四面体Si-O晶胞中裂纹尖端张开距离和O-Si-O角的跟踪，研究了裂纹尖端钝化过程。我们比较了Al-O和Si-O的断键行为。结果表明，Si-O键断裂是裂纹扩展的主要原因。根据模拟结果确定了临界应力强度因子和临界能量释放率。
The atomic‐scale cracking mechanism in clay is vital in discovering the cracking mechanism of clay at the continuum scale in that clay is a nanomaterial. In this article, we investigate mechanisms of modes I and II crack propagations in pyrophyllite and Ca‐montmorillonite with water adsorption through reactive molecular dynamics (MD) with a bond‐order force field. Clay water adsorption is considered by adding water molecules to the clay surface. During the equilibration stage, water adsorption could cause bending deformation of the predefined edge crack region. The relatively small orientating angle of water molecules indicates the formation of hydrogen bonds in the crack propagation process. The peak number density of adsorbed water decreases with the increasing strains. The atomistic structure evolution of the crack tip under loading is analyzed to interpret the nanoscale crack propagation mechanism. The numerical results show that the crack tip first gets blunted with a significant increase in the radius of the curvature of the crack tip and a slight change in crack length. The crack tip blunting is studied by tracking the crack tip opening distance and O–Si–O angle in the tetrahedral Si–O cell in modes I and II cracks. We compare bond‐breaking behaviors between Al–O and Si–O. It is found that Si–O bond breaking is primarily responsible for crack propagation. The critical stress intensity factor and critical energy release rate are determined from MD simulation results.