【作者】 付光俊；

【导师】 沈海军；

【作者基本信息】 南京航空航天大学 ， 飞行器设计， 2007， 硕士

【摘要】 本硕士论文的工作包括两大部分,即,第一部分:金属铝氢脆特性的分子动力学计算模拟,第二部分: III～VA族元素纳米管熔化与拉伸特性的分子动力学模拟。第一部分:金属铝氢脆特性的分子动力学计算模拟金属铝质地轻,价格低廉,储量丰富,耐腐蚀,加工性能优良,易于其他金属组成高强度耐高温或耐低温的合金材料,被广泛应用于航空、航天、航海等领域。很多文献资料表明铝中氢原子能降低裂尖位错的临界应力强度因子和铝原子的结合能,弱化金属晶格,促进位错发射和运动,引起裂纹生长,并加快铝疲劳裂纹的扩展速率。这样,在航空航天航海等领域可能发生由于铝氢脆而导致蒙皮或结构裂纹,进而引起重大事故。因此在航空航天航海等领域对铝氢脆的研究具有重大意义。在本文第一部分,我们以航空、航海领域内,金属铝材料腐蚀环境中的氢脆现象为研究对象,采用“从下到上”的研究方法,使用分子动力学方法模拟了应力条件下铝单晶、双晶的氢脆特性,获得了铝单晶、双晶及其含氢模型在拉伸条件下构形变化情况和能量、应力与应变关系,从纳观层次探讨了飞机、船舶铝材氢脆的微观机制。第二部分:III～VA族元素纳米管熔化与拉伸特性的分子动力学模拟纳米碳管良好的力学、电学性能受到了全世界研究者们的广泛关注,作为准一维纳米材料家族中的重要成员,单壁硅、锗、碳化硅、氮化硼、氮化镓纳米管结构与单壁碳纳米管相似,它们是否拥有同碳纳米管一样优异的力学、电学性能,已成为当今基础和应用领域研究的热点。为此,第二部分采用经典的分子动力学方法来研究III～VA族元素纳米管熔化、拉伸力学性能。首先对III～VA族元素纳米管熔化进行了模拟,获得了升温过程中各纳米管的几何形态、原子径向分布,以及能量变化曲线,并系统分析了它们熔化特性的差异。然后研究了III～VA族元素纳米管轴向拉伸力学问题,获得了特定条件下各纳米管的杨氏模量、断裂应变、最大外载、径向收缩率等参数,并分析了六种纳米管轴向拉伸力学特性的差异。更多还原

【Abstract】 The thesis contains two parts, i.e. Part 1: MD(Molecular Dynamics) simulations on hydrogen embrittlement in aluminium metal materials, and Part 2: MD simulations of the melting and tensional properties of Group III-VA element nanotubes.Part1: MD simulations on hydrogen embrittlement in aluminium metalAluminium metal has many excellent properties, such as light weight, cheap price, abundant reserves, anti-corrosion properties, excellent machining capabilities, high strength and convenient synthesization with other metals into anti-high temperature or low temperature alloys, and is widely used in aeronautics,astro- nautics and navigation scopes. Many literatures and data indicate hydrogen-atoms in aluminium can reduce binding energy and critical stress intensity factor at crack tips, debase crystal lattice of metal, accelerate dislocation growth and mobility, induce crack or fatigue-crack growth in aluminium. Thus, it will result in the fatal accident on account of hydrogen embrittlement in aluminium. So it is necessary to investigate hydrogen embrittlement of aluminium in the aeronautics, astronautics and navigation scopes. Molecular Dynamics simulations were performed in the first part to investigate the properties of hydrogen embrittlement in single crystal and bicrystal aluminium by the down-to-up methods, the configurations and relations of energy/stress and strain were obtained. The mechanism of hydrogen embrittlement in aluminium was discussed at nanometer level.Part2: MD simulations of the melting and mechanical property of Group III-VA element nanotubesDue to the excellent mechanical property and the electrical property,carbon nanotubes were paid much attentions by researchers all over the world. As the important members of one-dimension nano-materials, single-walled silicon, germ- anium, carborundum, boron nitrogen, gallium nitrogen nanotubes hold similar structure to single-walled carbon, and have become hotspot in the field of micro- electron, physics and marerial. Whether do they have outstanding mechanical property similar to carbon nanotube?In this part, molecular dynamics simulations were performed to investigate their properties of melting and mechanics. Firstly, the melting of the III-VA group element nanotubes is simulated by MD, the molecular configurations, pair correlation function and energy changes of the nanotubes during the heating-up are obtained, and the differences of their melting properties are discussed systematically. Secondly, the mechanical properties of the III-VA group element nanotubes are investigated through MD simulations. We obtained Young’s modulus, fracture strain, critical load, radial shrinkage ratio of the III-VA group element nanotubes, and analyzed the differences of their mechanical properties.更多还原