摘 要

石墨烯是一种二维的碳原子晶体，从2004年被科学家用一种简单的机械分离法得到后，便受到材料科学界的瞩目。通过研究分析发现石墨烯不但具有高导电性、高热导率、高透光性等特性，在传感器元件、污水处理、能源储存、光电探测等领域有很高的应用潜力，而且结构特殊，强度和刚度都令人惊奇。如今在各个领域上，石墨烯的研究应用都已经了初步的进展，并验证了其材料性能的显著优势，可因为尚处于研究初期，面临诸多的技术难题，制备方法并未成熟。因制备方法困难，最终得到的石墨烯的实际特性与理论猜想不符。这种差异性可能是制备的石墨烯薄膜中存在的缺陷所导致的，于是为了了解石墨的性能，改进和发展石墨烯的生产工艺，有必要进一步研究石墨烯缺陷的影响。这次研究中，为避免制备麻烦、实验困难等问题，采用计算机数值模拟的方式，首先建立了含不同形状缺陷的石墨烯模型，再模拟单层石墨烯拉伸的过程，测量各个模型的机械性质，进而探讨是否能通过改变缺陷形状来实现对石墨烯力学性能的调控。

本文使用LAMMPS软件，选择AIREBO势函数为基础，分别模拟研究了理想的无缺陷石墨烯和含不同形状缺陷的石墨烯薄膜在单向拉伸历程中的力学行为，记录了不同缺陷石墨烯的变形破坏过程，得到了相应的缺陷石墨烯的应力-应变曲线，并计算得到不同缺陷石墨烯的弹性模量，比照不同石墨烯的抗拉强度以及拉伸极限应变，对比分析缺陷对石墨烯拉伸力学性能的影响。

从结果上看，石墨烯的拉伸过程主要是四个阶段：材料先弹性变形，之后开始屈服，接着塑性变形中不断强化，最后直接断裂。分析石墨烯的变形前后状态，可得知缺陷对石墨烯的机械特性影响较大。

缺陷的存在会明显降低石墨烯薄膜的弹性模量，降低幅度和缺陷的形状和位置有关。观察应力-应变曲线，得知存在缺陷的石墨烯的拉伸强度和极限拉伸应变均呈明显的下滑趋势，缺陷的形状对拉伸强度的改变影响较大，不同形状的缺陷导致石墨烯的拉伸强度下降的程度不同，但对极限拉伸应变的下降的影响区别不大。在拉伸载荷的作用下，完整无缺陷的石墨烯破坏往往是从边缘处开始，而有缺陷的石墨烯材料于缺陷边缘处最开始发生形变以致断裂。研究可知通过控制缺陷的形状和位置可以实现对石墨烯力学性能的调节，使其更符合实际应用中的力学性能要求。

关键词： 分子动力学；石墨烯；缺陷形状；力学性质

Abstract

Graphene, a two-dimensional crystal of carbon atoms, has been in the spotlight of materials science since 2004, when it was made by using a simple mechanical separation process.Through research and analysis, it is found that graphene not only has high electrical conductivity, high thermal conductivity and high light transmittance, but also has high application potential in sensor elements, sewage treatment, energy storage, photoelectric detection and other fields. In addition, it has a special structure, and its strength and stiffness are amazing.At present, the application and development of graphene in various fields have been preliminarily studied and its significant advantages in material properties have been verified. Notwithstanding, the manufacturing technique is not yet grown because it is still in developmental stage of indagation and confront a lot of technical matters.Due to the difficulty in preparation, the actual properties of the graphene materials are often different from the theoretical properties.We suspect that the differences in the results are due to defects. Therefore, in order to understand the properties of graphite and to improve and develop the production process of graphene, it is necessary to further study the impact of graphene defects.Preparation in this article, in order to avoid trouble, difficult issues such as the experiment, with the method of computer numerical simulation, using molecular dynamics method for single layer graphene film process of uniaxial tension is simulated, and build the former of graphene with varying deficiency, then probe into the impact of unlike bugs on the tensile mechanical properties of graphene, discusses whether can pass the defect to change shape to achieve on the mechanical properties of graphene later.

Using LAMMPS software, this paper adopts AIREBO potential function, respectively, to study the ideal of zero defect of graphene and graphene films containing different shape defects in the process of the unidirectional tensile mechanical behavior, recorded the deformation and failure process of different defects graphene,.The stress-strain curves of different graphene defects were drawn, and then the elastic modulus was calculated using hooke's law. The tensile strength and ultimate strain values of graphene were important parameters. By comparing them, the effect of bugs on the tensile mechanical properties of graphene could be analyzed.

According to the observation, the tensile process of graphene mainly consists of four stages: elastic phase, yield phase, strengthening time and local deformation moment.The bugs can obviously alter the mechanical quality of graphene.

The presence of defects significantly reduces the elastic modulus of the graphene film, which is related to the shape and location of the defects.Observe the stress-strain curve, learned that defects in graphene both tensile strength and ultimate tensile strain is obvious downward trend, affected by the change of the shape of the defects on tensile strength, different shapes of defects resulting in a decline in the tensile strength of the graphene degree is different, but for the ultimate tensile strain of the decline in the influence of the difference is not big.Under the action of tensile load, the complete and defect-free graphene failure usually starts at the edge, while the defective graphene material initially deforms and breaks at the edge of the defect.According to the study, the mechanical properties of graphene can be adjusted by controlling the shape and position of defects, so that the mechanical properties of graphene can be more in line with the requirements of practical application.

Key Words：Molecular dynamics；graphene；shape of flaw；mechanical property

目 录

第一章 绪论 １

1.1石墨烯简介 １

1.1.1石墨烯的结构和性质 １

1.1.2石墨烯的制备方法 ２

1.1.3石墨烯的应用前景 ３

1.2石墨烯力学性质研究现状 ４

1.3本文的研究目的与内容 ４

第二章 分子动力学的基本原理和计算方法 ６

2.1引言 ６

2.2分子动力学模拟方法 ６

2.2.1基本原理 ６

2.2.2积分算法 ７

2.2.3相互作用势 ８

2.2.4系综理论和温度控制方法 １０

2.3分子动力学模拟流程 １１

2.4 本章小结 １２

第三章 对缺陷石墨烯拉伸变形的分子动力学模拟 １３

3.1引言 １３

3.2 物理模型和模拟方法 １３

3.2.1单层石墨烯薄膜几何模型的建立 １３

3.2.2 模拟方法及过程 １５

3.3 模拟结果及分析 １５

3.3.1拉伸过程的应力-应变曲线 １５

3.3.2 缺陷对石墨烯弹性模量的影响 １７

3.3.3 缺陷对石墨烯抗拉强度的影响 １７

3.3.4 石墨烯拉伸变形破坏形态分析 １８

第四章 总结和展望 ２０

4.1总结 ２０

4.2展望 ２０

参考文献 ２１

致 谢 ２２

第一章 绪论

1.1石墨烯介绍

1.1.1石墨烯的结构和性质

大家都知道碳元素在地球上是最普遍的元素之一，是构成人类生命体和日常所需元素中必不可少的，广泛分布于自然界各类矿石和部分有机物中。碳的发展历程久远，用途广泛，在材料史上有着举足轻重的地位。自第二次工业革命以来，人们不断发现和利用碳元素的多变性，开发出了如纳米金刚石、富勒烯、碳纳米管等一系列的新型碳材料。图1.1为几种主要的碳同素异形体结构示意图。