本文選題：手性納米管 + 分子動力學(xué)模擬��； 參考：《南京師范大學(xué)》2015年碩士論文

【摘要】：碳納米管自發(fā)現(xiàn)以來就被譽為未來的材料,根據(jù)其獨特的力學(xué)特性,可以制作很多有廣泛應(yīng)用前景的納米器件,譬如在搭建扭轉(zhuǎn)式振蕩器時,納米管可以作為彈簧元件；在搭建納米發(fā)電機時,納米管可以作為旋轉(zhuǎn)軸承等。在這些應(yīng)用中,納米管的扭轉(zhuǎn)性能對納米器件系統(tǒng)極為重要。本文采用分子動力學(xué)模擬的方法探討了手性碳管扭轉(zhuǎn)的力學(xué)行為,并分析了長度、半徑、轉(zhuǎn)速、缺陷等對手性碳管扭轉(zhuǎn)過程中力學(xué)性質(zhì)的影響。取得了一些有意義的結(jié)果：(1)從整體上看,碳管正(反)向扭轉(zhuǎn)都經(jīng)歷了四個階段,前面三個階段,扭矩隨切應(yīng)變的增加而增加,但是扭矩曲線的斜率逐級減小,第四階段,碳管扭轉(zhuǎn)破裂,扭矩陡降,積累的能量迅速釋放。(2)隨著扭轉(zhuǎn)角的增加,碳原子離管軸平均距離單調(diào)減小,碳管中的碳原子整體上做靠近軸向的運動,管內(nèi)空間持續(xù)下降。(3)手性碳管在扭轉(zhuǎn)過程中,中間部分的碳原子應(yīng)力增加的最快,而左右兩部分的碳原子所受到的應(yīng)力則較慢,碳管中部原子的局部環(huán)境率先出現(xiàn)明顯改變,先于其他部位受到較大的應(yīng)力,隨后逐漸將應(yīng)力向兩邊傳遞,從而使整個碳管上的碳原子所受的應(yīng)力得以增大,導(dǎo)致形變結(jié)構(gòu)以“扭結(jié)”的方式向兩邊展開。(4)正向扭轉(zhuǎn)的軸向力隨扭轉(zhuǎn)角單調(diào)上升,使碳管趨于伸長,當扭轉(zhuǎn)越過屈服點后,軸向收縮力開始持續(xù)下降到零,并最終完成方向的反轉(zhuǎn)而使碳管轉(zhuǎn)為軸向收縮；而反向扭轉(zhuǎn)的軸向力從開始就體現(xiàn)出收縮特性,軸向收縮力大小隨扭轉(zhuǎn)進程單調(diào)增大。當碳管正(反)向扭轉(zhuǎn)越過屈服點后之后,軸向收縮力以更大的增速隨扭轉(zhuǎn)角增大,體現(xiàn)為在碳管扭轉(zhuǎn)彈性屈服點后有更大的軸向彈性模量,且軸向彈性模量隨著管長的增加而減小。(5)手性角在約15°之前,正向扭轉(zhuǎn)對應(yīng)的屈服角隨手性角的增加而減小,反向扭轉(zhuǎn)對應(yīng)的屈服角隨手性角增加而增大；當手性角超過15°時,正向扭轉(zhuǎn)的屈服角轉(zhuǎn)而增大,而反向扭轉(zhuǎn)的屈服角卻開始減��；即手性碳管扭轉(zhuǎn)時,手性角在15°左右的碳管反向扭轉(zhuǎn)的彈性扭轉(zhuǎn)范圍最大,能承受的應(yīng)變最大,正向扭轉(zhuǎn)的彈性扭轉(zhuǎn)范圍最小,能承受的應(yīng)變也最小。(6)當碳管扭轉(zhuǎn)速率小于等于1°/ps,系統(tǒng)始終處于準平衡狀態(tài),即系統(tǒng)在每一步的扭轉(zhuǎn)過程中有足夠的弛豫時間達到平衡。當轉(zhuǎn)動速度大于1°/ps,系統(tǒng)開始偏離平衡態(tài),隨扭轉(zhuǎn)動速率的增加,扭矩曲線斜率增大,扭轉(zhuǎn)屈服角則先增大到一極值后再減小,而碳管斷裂的扭轉(zhuǎn)角單調(diào)下降。
[Abstract]:Carbon nanotubes (CNTs) have been regarded as the future materials since their discovery. According to their unique mechanical properties, carbon nanotubes can be used as spring elements in the construction of torsional oscillators. Nanotubes can be used as rotating bearings in building nano-generator. In these applications, the torsional performance of nanotubes is very important for nanodevice systems. In this paper, the mechanical behavior of chiral carbon tube torsion is studied by molecular dynamics simulation, and the effects of length, radius, rotation speed and defects on the mechanical properties of chiral carbon tube torsion are analyzed. Some meaningful results have been obtained: (1) overall, the positive (reverse) torsion of the carbon tube has gone through four stages. In the first three stages, the torque increases with the increase of the shear strain, but the slope of the torque curve decreases step by step, the fourth stage. With the increase of torsion angle, the average distance of the carbon atom from the tube axis decreases monotonously, and the carbon atom in the carbon tube moves near the axis as a whole. In the process of torsion, the stress of carbon atoms in the middle part of the tube increases fastest, while the stress of the carbon atoms in the left and right parts of the tube is slower, and the local environment of the atoms in the middle part of the tube changes obviously. The stress on the carbon atoms in the whole carbon tube is increased by the larger stress on the other parts of the tube, and then the stress is gradually transferred to the two sides of the tube, so that the stress on the carbon atoms in the whole carbon tube can be increased. The axial force of the forward torsion increases monotonously with the torsion angle, which makes the carbon tube tend to elongate. When the torsion crosses the yield point, the axial contraction force begins to decrease to zero. The axial force of the reverse torsion shows the characteristics of shrinkage from the beginning, and the magnitude of the axial contraction force increases monotonously with the torsion process. When the positive (reverse) torsion of the carbon tube passes the yield point, the axial contraction force increases with the increase of the torsion angle, which is reflected in the greater axial elastic modulus of the carbon tube after the torsional elastic yield point. And the axial modulus of elasticity decreases with the increase of the length of the tube.) the chiral angle decreases with the increase of the yield angle of the forward torsion before about 15 擄, and the yield angle of the reverse torsion increases with the increase of the chiral angle, and when the chiral angle exceeds 15 擄, the corresponding yield angle increases with the increase of the chiral angle. The yield angle of positive torsion increases, but the yield angle of reverse torsion begins to decrease, that is, when the chiral carbon tube torsion, the elastic torsion range of the chiral carbon tube with a chiral angle of about 15 擄is the largest and the strain is the largest. When the torsion rate of carbon tube is less than or equal to 1 擄/ s / s, the system is always in a quasi-equilibrium state, that is, the system has sufficient relaxation time to achieve equilibrium in each step of torsion. When the rotational velocity is greater than 1 擄/ ps, the system begins to deviate from the equilibrium state. With the increase of the torsional dynamic rate, the slope of the torque curve increases, the torsional yield angle increases to an extreme value and then decreases, while the torsional angle of the carbon tube fracture decreases monotonously.
【學(xué)位授予單位】：南京師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：O613.71;TB383.1

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