介观尺度下石墨烯泡沫的力学行为及其物理本性

As an advanced porous material, graphene foam (GF) materials have important applications in the fields of intelligent device, biosensor, and aerospace, as well as environmental protection. They have obtained more and more extensive concerns in the material science, energy engineering and regenerative medicine, due to their outstanding mechanical, electromagnetic and thermoacoustic properties. Currently, few theoretical and/or computational studies have evaluated the constitutive relationship and corresponding micro/nanostructural mechanisms of physical properties and mechanical behaviors exhibited in experiments. In this project, we by means of coarse-grained molecular dynamics simulations, launches a systematic and thorough study based on the mesoscale (100nm~0.1μm) for the relationship between the microstructures and macroscopic mechanical properties of the GF, and hence the study will provide a theoretical guidance to the optimal design of new advanced graphene-based porous materials with high cost-performance. On this basis, the project will further establish a viscoelastic constitutive model within a small deformation range for the materials during the loading, according to the continuum median theory. The dependability of the constructed model and the corresponding parameters will be evaluated and identified through the auxiliary mechanical experiments, in order to predict the deformation for GF-based structural components of the bionic and smart devices.

作为一种先进的多孔材料，石墨烯泡沫在智能器件、生物传感、航空航天以及环境保护等领域有着重要的应用价值，其表现出的优异的机械，电磁，热声性能在能源工程界，材料科学界甚至再生医学界都受到了日益广泛的关注。然而，国内外关于该类材料的研究报道基本上还局限于实验现象本身，缺少具体的计算模型来揭示其内在的物理机制，也没有明确的本构关系来描述其外在的力学行为。本项目立足于介观尺度（百纳米至亚微米），借助于粗粒化分子动力学模拟，对石墨烯泡沫骨架结构与宏观力学性能的相互关联开展系统深入的机理研究，为设计性能优异且经济适用的新型三维石墨烯多孔材料提供理论参照。在此基础上，本项目还进一步从连续介质理论出发，为石墨烯泡沫在小变形范围内对外载的响应确立粘弹性本构关系；通过辅助力学实验来检验所建模型的可靠性，并识别模型参数，力图对以该材料为结构承载元的仿生器件或智能设备提供变形预测。

以无序堆砌为主要建构方式铰接而成的三维多孔材料—石墨烯泡沫，由于兼备了石墨烯与多孔材料的优点而备受国内外科技界关注。但就已有的实验研究来看，该泡沫优异力学行为背后的物理机制尚不清楚，准二维石墨烯重组为三维网络的应力传递特性也缺乏理解，石墨烯泡沫受外载时的介观动力学演化过程更是无法原位再现。通过青年基金的三年资助，本项目在准二维石墨片模型的基础上，构建了一种同时含有本征孔和铰链键的三维孔片网络拓扑模型。在引入了铰链键力场参数和孔片比特征几何量后，借助粗粒化动力学方法，合理地实现了对拟真实石墨烯泡沫力学行为的有效评估。在此基础上，用动态分析的方式揭示了局部微结构的动力学演化过程，并结合Virial应力云图从连续统的角度深入分析了这种拟真实体系的应力传递细节。最后，本项目为解决已有模型在尺寸和拓扑两个方面的局限性，还进一步构建了一种三阶石墨烯泡沫粗粒化模型，并且在定量描述石墨烯泡沫超压缩力学行为的本构关系方面给出了一个割线模量标度律。