【摘要】：高超聲速環(huán)境下材料的燒蝕破壞問(wèn)題是發(fā)展高超聲速飛行器技術(shù)的關(guān)鍵問(wèn)題。本文主要應(yīng)用分子動(dòng)力學(xué)方法對(duì)石墨受到高超聲速氧分子流燒蝕過(guò)程進(jìn)行了模擬研究。本文的主要工作有以下幾個(gè)方面:(1)運(yùn)用基于Reax FF力場(chǎng)勢(shì)的分子動(dòng)力學(xué)方法模擬了雙層以及三層石墨與高超聲速氧分子流的相互作用過(guò)程。石墨在高超聲速氧分子流的持續(xù)沖擊作用下,氧原子與表層石墨原子結(jié)合;可以觀察到部分結(jié)合了氧原子的碳原子以CO2的形式從表層石墨解離,石墨出現(xiàn)缺陷,逐漸破壞。另外發(fā)現(xiàn)三層石墨的情況下表層石墨溫度上升速度較慢。(2)運(yùn)用基于REBO勢(shì)的分子動(dòng)力學(xué)方法對(duì)多層石墨受高超聲速氧分子流的燒蝕過(guò)程進(jìn)行了模擬。對(duì)LAMMPS中只包含碳、氫原子的REBO勢(shì)函數(shù)進(jìn)行修改,加入氧原子。分析了石墨氧化對(duì)其等效面內(nèi)剛度的影響。研究發(fā)現(xiàn),多層石墨在受到高超聲速氧分子流沖擊燒蝕過(guò)程中出現(xiàn)逐層破壞的現(xiàn)象,且模擬隨著層數(shù)的增多,石墨破壞的時(shí)間相對(duì)延后。研究了缺陷對(duì)雙層石墨受高超聲速氧分子流沖擊燒蝕過(guò)程的影響,發(fā)現(xiàn)雙空位缺陷加速了表層石墨升溫破壞的過(guò)程,單空位缺陷的影響次之,而Stone-Wales型缺陷對(duì)燒蝕過(guò)程的影響可以忽略。氧原子以吸附的方式與石墨結(jié)合對(duì)其等效面內(nèi)剛度基本沒有影響,而在缺陷處與碳原子結(jié)合則降低了石墨的等效面內(nèi)剛度。(3)對(duì)研究石墨燒蝕問(wèn)題時(shí),分子動(dòng)力學(xué)方法的可計(jì)算規(guī)模進(jìn)行了探討。運(yùn)用基于REBO勢(shì)的分子動(dòng)力學(xué)方法采用單核計(jì)算對(duì)包含33516個(gè)碳原子,12000個(gè)氧原子的系統(tǒng)進(jìn)行300ps的模擬,時(shí)間步長(zhǎng)為1fs。總的計(jì)算機(jī)時(shí)約為10個(gè)小時(shí),這相對(duì)于采用Reax FF力場(chǎng)勢(shì)所能計(jì)算的規(guī)模有了很大的提高。另外詳細(xì)描述了表層石墨在受高超聲速氧分子流沖擊作用過(guò)程中從缺陷產(chǎn)生、缺陷擴(kuò)展到破壞解體的階段性現(xiàn)象,分析了模擬過(guò)程中表層石墨的溫度和系統(tǒng)勢(shì)能的變化。
[Abstract]:The problem of material ablation in hypersonic environment is a key problem in the development of hypersonic vehicle technology. In this paper, the molecular dynamics method is used to simulate the process of supersonic oxygen molecular ablation of graphite. The main work of this paper is as follows: (1) the interaction process of two-layer and three-layer graphite with hypersonic oxygen flow is simulated by using the molecular dynamics method based on Reax FF force field potential. Under the continuous impact of hypersonic oxygen molecule flow, the oxygen atom binds to the surface graphite atom, and it can be observed that the carbon atom which binds oxygen atom dissociates from the surface graphite in the form of CO2, and the graphite appears defects and gradually destroys. In addition, it is found that the temperature of surface graphite rises slowly in the case of three layers of graphite. (2) the ablation process of multilayer graphite subjected to hypersonic oxygen flow is simulated by molecular dynamics method based on REBO potential. The REBO potential function containing only carbon and hydrogen atoms in LAMMPS is modified and oxygen atoms are added. The effect of graphite oxidation on the equivalent in-plane stiffness was analyzed. It is found that the multi-layer graphite is destroyed layer by layer in the process of supersonic oxygen molecular flow impact ablation, and the time of graphite destruction is relatively delayed with the increase of the number of layers. The effect of defects on the ablation process of double layer graphite by hypersonic oxygen molecular flow is studied. It is found that the double vacancy defect accelerates the process of surface graphite heating destruction, and the effect of single vacancy defect is the second. However, the effect of Stone-Wales defects on the ablation process can be neglected. The adsorption of oxygen atoms with graphite has little effect on the in-plane equivalent stiffness of graphite, but it decreases the equivalent in-plane stiffness of graphite by bonding with carbon atom at defects. (3) when studying the problem of graphite ablation, The computational scale of molecular dynamics method is discussed. The molecular dynamics method based on REBO potential was used to simulate the 300ps of a system containing 33516 carbon atoms and 12,000 oxygen atoms with a time step of 1fs. The total computer time is about 10 hours, which is much higher than that calculated by using the Reax FF force field potential. In addition, the phase phenomenon of surface graphite produced from defect to destruction and disintegration during the process of hypersonic oxygen molecular flow impact is described in detail. The temperature and system potential energy of surface graphite in the simulation process are analyzed.
【學(xué)位授予單位】：南京航空航天大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：V219

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本文編號(hào)：2319858