纳米晶甲烷水合物的蠕变失稳
Mechanical Creep Instability of Nanocrystalline Methane Hydrates
摘要：
天然气水合物（NGH）的力学蠕变行为对于理解地球上含水合物沉积物的力学不稳定性具有重要意义。受限于实验的挑战，纳米晶甲烷水合物的内在蠕变机制在很大程度上仍然是未知的，但在分子尺度。本文采用大尺度分子动力学模拟方法研究了纳米晶甲烷水合物的蠕变行为。结果表明，力学蠕变响应在很大程度上取决于内部微观结构的晶粒尺寸和外部条件的温度和静态应力。有趣的是，在纳米晶甲烷水合物中观察到长稳态蠕变，这可以通过修改的本构Bird-Dorn-Mukherjee模型来描述。微观结构分析表明，晶粒变形、晶界扩散和晶界滑移共同控制了纳米晶甲烷水合物的蠕变行为。此外，结构转变在其机械蠕变机制中也显得重要。这项研究为理解天然气水合物的机械蠕变情景提供了新的见解。
英文摘要：
Mechanical creep behaviors of natural gas hydrates (NGHs) are of importance for understanding mechanical instability of gas hydrate-bearing sediments on Earth. Limited by the experimental challenges, intrinsic creep mechanisms of nanocrystalline methane hydrates remain largely unknown yet at molecular scale. Herein, using large-scale molecular dynamics (MD) simulations, mechanical creep behaviors of nanocrystalline methane hydrates are investigated. It is revealed that mechanical creep responses are greatly dictated by internal microstructures of crystalline grain size and external conditions of temperature and static stress. Interestingly, a long steady-state creep is observed in nanocrystalline methane hydrates, which can be described by a modified constitutive Bird-Dorn-Mukherjee model. Microstructural analysis show that deformations of crystalline grains, grain boundary (GB) diffusion and GB sliding collectively govern the mechanical creep behaviors of nanocrystalline methane hydrates. Furthermore, structural transformation also appears important in their mechanical creep mechanisms. This study sheds new insights into understanding the mechanical creep scenarios of gas hydrates.
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