超轻大块气凝胶力学行为的大规模数值模拟

Ultralight materials, such as aerogels, exhibit spectacular mechanical, physical, and thermal properties. Experimental and theoretical characterizations of these materials are leading to greater understanding of various phenomena associated with these materials, allowing for greater customizability to suit various applications. For example, silica aerogels have several highly desirable properties including being environmentally safe, having large thermal resistance, making them very suited for applications such as thermal insulation of the Mars rovers, Spirit and Opportunity. In this project, massively parallel molecular dynamics will be employed to investigate accurate modeling of ultralight materials, and to determine their mechanical and physic properties. Open-source software such as the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) allows for rapid upscaling of simulation sizes in computational clusters, enabling the simulation of phenomena at scales ranging from the atomic to the nano- and micro-scale. Examples of these phenomena include precise simulations of the extensive pore sizes and pore distribution of silica aerogels, enabling more accurate numerical characterization of aerogel’s geometrical, thermal and mechanical properties. These models could be extended further, through multiscale coupling and modeling, to model phenomena at even larger scale lengths.

气凝胶是一种超轻材料，其密度为水的0.3%-50%，具有卓越的力学和物理学特征。硅气凝胶具有环保、高热阻等特性，开始应用于航空航天工程，火星探测器精神号和机遇号都采用了硅气凝胶。目前，未见有关此类超轻材料力学行为的精确模拟及描述的研究报道。本课题拟通过大规模并行分子动力学模拟，研究超轻大块硅气凝胶的力学行为，建立其本构模型。利用LAMMPS软件升级计算集群的计算规模，实现从原子量级上升到纳米甚至微米级的大规模数值模拟。通过其几何构型的精确描述，重点研究大块硅气凝胶中的空隙尺寸与分布对其力学行为的影响。此模型可通过多尺度耦合与建模得到进一步的扩展，来描述更大尺度气凝胶材料的力学和物理特征。

气凝胶是一种超轻纳米多孔材料，其密度低至水密度的0.3%，具有卓越的力学与物理特性。硅气凝胶是目前气凝胶材料中制备工艺最为成熟，研究最为广泛的一类，它具有环保、高热阻，高声阻等优越的特性，目前已经被应用在航天工程，军事工程，高能物理等领域。本课题通过分子动力学对硅气凝胶材料的大规模模拟，建立了硅气凝胶的分子动力学模型，并对其力学与物理性能进行了深入的探究。首先我们采用开源分子动力学软件LAMMPS建立了硅气凝胶的微观模型，采用不同的方法研究了其特征参数热传导率和杨氏模量。研究结果表明，热传导率的模拟结果与其他学者的实验结果相近；杨氏模量与密度之间幂指数为3.168的幂律关系与其他学者的实验结论相符合。进一步，考虑到硅气凝胶的分形结构，又提出了描述大块硅气凝胶结构的两级模型，利用硅气凝胶的结构参数，如密度，内部纳米颗粒平均直径，表面积与体积比，结合理论推导与数值模拟，推导出了预测其杨氏模量的表达式。本课题工作旨在加深对硅气凝胶各项性能的理解，并推进其在各个领域中的实际应用。