【摘要】：石墨烯具有塊體材料無(wú)法比擬的優(yōu)良力學(xué)性質(zhì),被認(rèn)為是具有戰(zhàn)略意義的新材料,可望在納電子器件、能量存儲(chǔ)、生物醫(yī)藥及場(chǎng)發(fā)射材料等領(lǐng)域獲得廣泛應(yīng)用,具有非常廣闊的應(yīng)用前景。由于獨(dú)特的二維平面特性,研究石墨烯力學(xué)、摩擦等性質(zhì)對(duì)石墨烯產(chǎn)品的制備有著非常重要的意義�；诜肿觿�(dòng)力學(xué)理論,本文首先模擬了雙層石墨烯的納米壓痕過(guò)程,討論了Lernnard-Jones勢(shì)函數(shù)的截?cái)喟霃阶罴阎狄约暗贸隽说湫偷妮d荷-位移曲線。接著以壓頭數(shù)目、溫度、尺寸效應(yīng)等因素為主要考察指標(biāo)分析了其對(duì)石墨烯力學(xué)性能的影響。得出雙層完美石墨烯薄膜彈性模量和強(qiáng)度分別為0.897 TPa和197.3 GPa。石墨烯的力學(xué)性能對(duì)溫度以及壓頭尺寸有較強(qiáng)的依賴性。目前生產(chǎn)的石墨烯含有各種缺陷,相較于完美石墨烯,其仍有較大應(yīng)用價(jià)值。因此有必要研究和掌握缺陷對(duì)石墨烯性能的影響,以便在目前的生產(chǎn)技術(shù)下,推動(dòng)其工業(yè)化應(yīng)用。在完美石墨烯壓痕模型的基礎(chǔ)上,建立含缺陷石墨烯壓痕模型,重點(diǎn)探討Stone-Thrower-Wales、空位以及圓孔缺陷對(duì)石墨烯力學(xué)性能的影響。得出結(jié)論:薄膜中心存在STW和空位缺陷時(shí),石墨烯的彈性模量略有降低,而破壞強(qiáng)度下降幅度特別明顯�？瘴蝗毕菰趬侯^半徑范圍內(nèi)存在時(shí),臨界載荷與缺陷到薄膜中心的距離呈線性增長(zhǎng)比例關(guān)系;缺陷數(shù)目越多,其楊氏模量、破壞強(qiáng)度等就越低。薄膜中心存在的圓孔缺陷半徑越大,則其對(duì)薄膜的影響范圍越大。在壓頭范圍外存在圓孔缺陷的數(shù)目多或半徑達(dá)到一定尺度后,將會(huì)使石墨烯的力學(xué)性質(zhì)顯著降低。本文結(jié)論也說(shuō)明石墨烯結(jié)構(gòu)穩(wěn)定,對(duì)小缺陷不敏感,缺陷石墨烯仍具有較好的性能和使用價(jià)值。最后模擬了四層石墨烯的納米劃痕過(guò)程,特別對(duì)劃痕深度,速度以及劃痕方向等因素與石墨烯摩擦特性之間的關(guān)系進(jìn)行了研究。得出結(jié)論:劃痕深度大小不同,石墨烯表現(xiàn)出的摩擦特性也不同。當(dāng)劃痕深度較小時(shí)摩擦力曲線非常光滑并具有正弦周期性,波動(dòng)周期約為2.45?,基本等于石墨烯的晶格常數(shù)2.46?,石墨烯處于超低摩擦狀態(tài)。當(dāng)劃痕深度較大時(shí)會(huì)導(dǎo)致石墨烯層間表現(xiàn)出交聯(lián)現(xiàn)象,交叉連接原子數(shù)目的增多導(dǎo)致了摩擦系數(shù)的增高。在一定劃動(dòng)速度范圍內(nèi),石墨烯薄膜的摩擦力并不隨著速度的改變而變化,只是由基體的晶格常數(shù)大小來(lái)決定。不同劃痕方向的摩擦力振幅不一致且波動(dòng)周期也有一定的差別,摩擦系數(shù)表現(xiàn)出明顯的各向異性。
[Abstract]:Graphene is considered to be a new material of strategic significance because of its excellent mechanical properties compared with bulk materials. It is expected to be widely used in nanoelectronic devices, energy storage, biomedicine and field emission materials. It has a very broad application prospect. Because of the unique two-dimensional plane characteristics, it is very important to study the mechanical and frictional properties of graphene for the preparation of graphene products. Based on the theory of molecular dynamics, the nanocrystalline indentation process of bilayer graphene is simulated, the optimal truncation radius of Lernnard-Jones potential function and the typical load-displacement curve are discussed. Then, the influence of pressure head number, temperature and size effect on the mechanical properties of graphene was analyzed. The elastic modulus and strength of the bilayer perfect graphene film are 0.897 TPa and 197.3 GPa., respectively. The mechanical properties of graphene have a strong dependence on temperature and pressure head size. The graphene produced at present contains all kinds of defects, and it still has great application value compared with perfect graphene. Therefore, it is necessary to study and master the effect of defects on the properties of graphene in order to promote its industrial application under the present production technology. Based on the perfect graphene indentation model, a graphene indentation model with defects was established, and the effects of Stone-Thrower-Wales, vacancies and circular hole defects on the mechanical properties of graphene were discussed. It is concluded that the elastic modulus of graphene decreases slightly with the existence of STW and vacancy defects in the center of the film, but the decrease of the fracture strength is especially obvious. The critical load increases linearly with the distance from the defect to the center of the film when the vacancy defect exists within the radius of the head, and the more the number of defects, the lower the Young's modulus and the failure strength. The larger the radius of circular hole defect in the center of the film is, the greater the influence range is on the film. The mechanical properties of graphene will be significantly reduced when the number of circular hole defects outside the pressure head range or the radius reaches a certain scale. The conclusion also shows that graphene is stable in structure, insensitive to small defects, and still has good performance and use value. Finally, the nano-scratch process of four layers of graphene is simulated, especially the relationship between the scratch depth, velocity and scratch direction and the friction characteristics of graphene is studied. It is concluded that the friction characteristics of graphene are different with different scratch depth. When the scratch depth is small, the friction curve is very smooth and has sinusoidal periodicity, the fluctuation period is about 2.45, which is basically equal to the lattice constant of graphene 2.46, and graphene is in the ultra-low friction state. When the scratching depth is high, the cross-linking between graphene layers will occur, and the increase of the number of cross-linked atoms will lead to the increase of friction coefficient. The friction force of graphene film does not change with the change of velocity, but only depends on the lattice constant of the substrate. The amplitude of friction force in different scratch directions is different and the fluctuation period is different. The friction coefficient shows obvious anisotropy.
【學(xué)位授予單位】：西安建筑科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：O613.71
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本文編號(hào)：2272413