Qin Hongfa, Liang Yingjing, Huang Jianzhang
Department of Engineering Mechanics, School of Civil Engineering, Guangzhou University, Guangzhou, 510640, China.
J Phys Condens Matter. 2020 Jan 16;32(3):035302. doi: 10.1088/1361-648X/ab49b0. Epub 2019 Oct 1.
Boron nitride nanosheets (BNNSs), a new type of wide bandgap nanomaterial, has attracted great attention due to their excellent properties and potential applications. Thus, it is necessary to have a comprehensive understanding of the mechanical properties of BNNSs in various working conditions. This paper presents an analytical model based on molecular mechanics to study the size effect and temperature effect on the Young's modulus of BNNSs. A closed-form formulation is derived for Young's modulus as a function of the length of B-N bonds and the out-plane displacement. It is shown that the chirality and the size of the BNNSs affect the length of BN bonds in molecular dynamic (MD) simulations. It is also found that the length of BN bonds and the out-plane displacement in a monolayer BNNS is remarkably temperature dependent. Therefore, the sizes and the temperatures can affect the Young's modulus of BNNSs. The expressions developed in this paper are employed to investigate the Young's modulus for zigzag and armchair BNNS with various sizes and temperatures. The present model, associating with a beam model, provides a simple method to calculate elastic properties which takes into account all bonded energies and force coefficient changes with atoms distance. The results of size effect and temperature effect are in good agreement with data of simulation performed in finite element method (FEM) simulation and MD simulation. The present study provides a molecular mechanics model to predict the Young's modulus of a monolayer BNNS, and the present model may be applied to other two-dimensional (2D) materials in further study.
氮化硼纳米片（BNNSs）是一种新型的宽带隙纳米材料，因其优异的性能和潜在的应用而备受关注。因此，有必要全面了解BNNSs在各种工作条件下的力学性能。本文提出了一种基于分子力学的分析模型，以研究尺寸效应和温度效应对BNNSs杨氏模量的影响。推导了杨氏模量作为B-N键长度和平面外位移函数的封闭形式表达式。结果表明，在分子动力学（MD）模拟中，BNNSs的手性和尺寸会影响B-N键的长度。还发现，单层BNNS中B-N键的长度和平面外位移显著依赖于温度。因此，尺寸和温度会影响BNNSs的杨氏模量。本文所推导的表达式用于研究不同尺寸和温度下锯齿形和扶手椅形BNNSs的杨氏模量。本模型与梁模型相结合，提供了一种计算弹性性能的简单方法，该方法考虑了所有键能和力系数随原子间距的变化。尺寸效应和温度效应的结果与有限元法（FEM）模拟和MD模拟得到的数据吻合良好。本研究提供了一个分子力学模型来预测单层BNNSs的杨氏模量，并且该模型在进一步研究中可能适用于其他二维（2D）材料。
