水化蒙脱石拉伸力学特性的分子动力学模拟研究
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华南理工大学 土木与交通学院

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TU443

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国家自然科学基金(11672108);国际(地区)合作与交流项目(11911530692)


Study on tensile mechanical properties of hydrated montmorillonite based on molecular dynamics
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School of Civil Engineering and Transportation,South China University of Technology

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    摘要:

    了解蒙脱石在拉伸状态下的力学行为在地球科学、岩土力学等领域至关重要,但现有的理论和方法难以在小间距范围内预测其水化力学性质及关键机理。本文通过编写施加应力-计算应变Perl语言脚本,首次进行了不同水化量蒙脱石拉伸应力下的分子动力学计算模拟与应力应变分析,确定了其不同应力阶段的力学特性、相互作用机制和微观结构演化。结果表明:蒙脱石内层水化对于极限应力和拉伸模量的弱化效应明显,且在水化初期弱化幅度会更大;体积水化膨胀主要源于晶格长度c的线性增长。Z方向的拉伸模量远小于平面内,即应力对表面Z方向的力学行为影响最大,当达到极限拉应力后,会出现整层分离的破坏现象;内层是大部分形变的主要原因,并且支配着蒙脱石的拉伸力学性能;Z方向拉应力主要造成晶格长度c和晶格角β的增加,而在X和Y方向拉应力下,则主要发生β的减少和增加。层电荷密度越高,结合水膜越密实,形成氢键数目越多,体积和晶格长度c越小,抗拉力学性能也越强。本工作定量揭示了蒙脱石在不同水化、拉应力状态、层电荷密度下的基本力学性质及内在结构机理,为岩土灾害宏(微)观防治、土体性质及工程适应性评价奠定了基础。

    Abstract:

    Knowing the mechanical behavior of montmorillonite (MMT) under tensile stress is crucial in earth science and geomechanics. However, existing theories and methods are difficult to predict its hydration mechanical properties and inner mechanism within the small layer-spacing. In this paper, through the stress-strain script, tensile molecular dynamics (MD) simulation and stress-strain analysis are conducted on MMT with different hydration amounts to determine the mechanical properties, interaction mechanism, and microstructure evolution. It is found that the weakening effect of interlayer hydration on ultimate stress and tensile modulus is obvious, and the weakening effect is greater in the early stage of hydration; the volume expansion with hydration results from the linear increase in lattice length c. The Z direction tensile modulus is much smaller than the in-plane, that is, the stress has the greatest influence on the mechanical behavior of surface Z direction; when the ultimate stress is reached, the layer separation failure occurs; besides, interlayer is the main cause of deformation and dominates the tensile mechanical properties of MMT; the tensile stress in Z direction causes the increase of lattice length c and lattice angle β, while in the X and Y directions, it is mainly the decrease and increase of β. The higher the layer charge density, the denser the bound-water film, the more hydrogen bonds formed, the smaller the volume and lattice length c, and the stronger the tensile mechanical properties. This work quantitatively reveals the basic mechanical properties and internal structure mechanism of MMT under different hydration, tensile stress, and layer charge density, laying a foundation for macro (micro) control of geotechnical disasters and evaluation of soil engineering performance.

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  • 收稿日期:2022-04-08
  • 最后修改日期:2022-07-30
  • 录用日期:2022-08-09
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