碳富勒稀分子C_n(n=20、60、80、180)的压缩力学特性

采用分子动力学与量子力学相结合(MD/QM)的方法,模拟了C_n(n=20、60、80、180)富勒稀分子的对径压缩过程,获得了各种富勒稀分子的系统能量-变形曲线、载荷-变形曲线、最大承受载荷、失效应变和压缩刚度等性能数据。研究结果表明,碳富勒稀分子具有出色的压缩力学性能,幻数n较大的富勒稀分子的最大承受载荷和压缩刚度也较大,但失效应变较小。     

冲击作用下薄壁金属空心球压缩变形研究

金属空心球结构是一种新型的多孔金属材料,对单个金属空心球在冲击作用下的压缩力学性能研究是对整体结构压缩力学性能研究的基础。该文研究了单个球壳冲击压缩特性,得到了单个金属空心球在冲击作用下的名义应力-应变曲线并与实验结果进行了对比验证,同时研究了径厚比和冲击速度对变形过程的影响。结果表明:名义应力-应变曲线和变形模态图显示其变形失效过程可分成六个阶段:局部压平、轴对称凹陷、多边形形成、内表面相互作用、侧壁失效以及密实阶段;径厚比越大,金属空心球越容易形成非对称的多边形形式,且在内表面相互作用阶段,上部壳体发生逆向翻转,侧壁发生了屈曲失效;径厚比较小时,在内表面相互作用阶段,下部壳体发生逆向翻转,侧壁发生了弯曲失效;冲击速度越大,底端壳开始发生凹陷的时间越早,空心球产生的不对称度越大。     

不同钙硅比水化硅酸钙力学性能的分子动力学模拟

基于Pellenq等的建模思路,构造了不同钙硅比(C/S)的水化硅酸钙(C-S-H)原子模型,采用分子动力学方法模拟了C-S-H在轴向拉伸载荷作用下的力学性能。重点比较分析了不同钙硅比的C-S-H在无水及含水情况下的拉伸应力-应变曲线。模拟结果表明:(1)与钙硅比为1.0的情况相比,钙硅比大于1.0时C-S-H结构的抗拉强度显著下降;(2)钙硅比大于1.0时,钙氧间的相互作用在承受载荷方面起重要作用,有效弥补了结构中因SiO_2基团缺失引起的缺陷,使得C-S-H的强度下降程度趋缓;(3)当应变达到一定程度时,水分子能够切断钙氧间的相互作用,使得C-S-H结构的强度进一步降低甚至引起断裂失效。     

金属丝网与金属橡胶材料的压缩特性对比研究

通过分析金属丝网垫和金属橡胶垫的制备工艺、细观特征并对其进行静态压缩试验,研究压缩变形量和密度对金属丝网垫和金属橡胶垫材料压缩力学性能的影响,从而分析这两种材料的承载能力和能量耗散特性。试验结果表明：金属丝网垫和金属橡胶垫材料的载荷-位移曲线具有相同的变化趋势且都具有刚度非线性特性;但是在相同的尺寸和密度下,金属橡胶垫的承载能力较金属丝网垫的承载能力强,且在相同的变形条件下金属橡胶的能量耗散能力较金属丝网垫的能量耗散能力强,即金属橡胶的阻     

管道失效判据简析

在外部载荷超过管道所能承受范围时管道即发生失效。通过研究管道在外力作用下的力学性能,有助于确定管道失效时的应力或应变的临界值,根据是取应力还是取应变作为衡量管道失效时的指标,分别有基于应力的失效判据和基于应变的失效判据。合理选用管道失效判据,可以节约管道投资、延长管道使用时间。简介材料应力—应变曲线的一般特征,分析管道基于应力的失效判据和基于应变的失效判据的方法。     

冲击载荷下圆环压缩变形特性研究

基于Johnson-Cook材料模型,应用数值模拟的方法,研究了圆环件在冲击载荷作用下的压缩变形规律。得到了冲击载荷下的摩擦系数-变形特性曲线,由此研究了不同载荷幅值(加载速度)、不同应变率敏感系数下的圆环内径变化规律以及对临界摩擦系数的影响。结果表明:摩擦系数-变形特性曲线和准静态结果基本趋势一致但有较大的差异,其中惯性效应起主要作用,应变率效应则起着次要作用。另外,此过程存在着临界摩擦系数,而应变率效应和惯性效应对圆环的临界摩擦系数影响不大,因此,临界摩擦系数可以作为试件的内在属性,应用于圆环的冲击锻压工程。     

碳纳米管增强开孔铝基复合泡沫的疲劳性能

采用原位化学气相沉积、短时球磨和填加造孔剂法相结合的工艺制备了碳纳米管(CNTs)/Al复合泡沫,研究了其在压缩-压缩循环载荷下的力学性能及失效机制。结果表明,CNTs/Al复合泡沫的应变-循环次数曲线经历线弹性、应变硬化及应变快速增长三个阶段。不同于泡沫铝的逐层坍塌变形失效模式,CNTs/Al复合泡沫疲劳失效的主要原因是大量剪切变形带的形成,试样出现快速的塑性变形。此外,CNTs含量为2.5wt%、孔隙率为60%的复合泡沫试样的疲劳强度相比于泡沫铝提高了92%。CNTs的均匀分布及增强相与基体材料之间良好的界面结合性保证了疲劳载荷能够以剪切力的形式从基体传递到CNTs上,使其充分发挥自身高强度、高韧性的特点,进而提高了疲劳性能。      

金属薄膜中微裂纹萌生行为的分子动力学研究

基体-薄膜结构是微电子器件中的典型结构,尤其是金属薄膜已被广泛的应用到微电子器件上。金属薄膜在制备过程中产生的表面微裂纹对薄膜的力学性能有着较大的影响,并且表面微裂纹尖端扩展所导致的薄膜破裂,更是造成薄膜失效的主要形式,因此对金属薄膜表面微裂纹萌生行为的研究具有重要的意义。本文基于分子动力学,对连续载荷作用下的带有缺陷的铜金属薄膜进行模拟分析。计算得到了系统在拉伸方向上的应力-应变关系曲线。模拟结果显示,金属铜薄膜的原子运动对整体力学行为有明显的影响。同时模拟过程中发现,在连续载荷作用下,大量位错在金属薄膜缺陷附近产生,从而促使薄膜表面萌生微裂纹。     

冲击载荷下环氧树脂动态压缩力学响应实验研究

为了从细观角度研究碳/环氧复合材料的动态力学性能,利用分离式霍普金森压杆实验装置对其组分材料TDE86#环氧树脂体系进行动态冲击压缩实验,获得不同应变率加载条件下环氧树脂的应力一应变曲线,基于应力-应变曲线分析了应变率对环氧树脂动态压缩力学性能的影响.研究结果表明:环氧树脂具有明显的应变强化效应,随着应变率的增加,环氧树脂的强度基本没有变化,最大应力时的应变逐渐减小,动态模量和压缩刚度有很大程度的提高.     

C/C复合材料压缩破坏的应变率效应研究

研究了碳布叠层/碳复合材料在四种不同应变率下的压缩性能, 对其在准静态、动态载荷下的压缩破坏机理进行了初步的探讨. 研究结果表明: C/C复合材料的压缩破坏强度具有较强的应变率效应, 与准静态(10^-4/s)相比, 复合材料的动态(1.5×10²/s)压缩强度可提高70%左右; 复合材料在准静态、动态载荷下力学性能的差异可归结为纤维与基体界面特性的应变率效应以及不同应变率下破坏模式的不同.     

C60,C180,C60@C180富勒烯分子的压缩力学特性与电子结构

采用分子动力学方法模拟了C60,C180,C60@C180富勒烯分子的压缩过程,用PM3半经验量子力学方法计算了压缩C60,C180,C60@C180分子的电子结构,讨论了C60,C180,C60@C180分子压缩力学特性的差异,以及电子结构在压缩过程中的变化．结果表明,由于分子几何构形上的差异,C60分子的承载与吸收能量能力显著高于C180和C60@C180分子,而CC60@C180分子略高于C180分子;C60分子具有最高的化学稳定性,而C60@C180分子的稳定性最低;C60和C60@C180分子的压缩变形越大,越容易失去电子,稳定性越低;C180分子在加载点处发生压缩“塌陷”时,化学活性明显增加．     

Mechanical properties and electronic structures of compressed C<Subscript>60</Subscript>, C<Subscript>180</Subscript> and C<Subscript>60</Subscript>@C<Subscript>180</Subscript> fullerene molecules

Molecular dynamics simulations were performed for compressed C₆₀, C₁₈₀ and C₆₀@C₁₈₀ fullerene molecules, and the semi-empirical PM3 calculations were carried out to obtain the electronic structure of the compressed fullerenes. According to the obtained results, the differences of mechanical properties between these compressed fullerenes, as well as the changes of their FMO (Frontier molecular orbital) energy-levels during compression, were discussed. It is shown that (1) the C₆₀ molecule has much higher load-support and energy-absorbing capability than the C₁₈₀ and C₆₀@C₁₈₀ molecules, and the C₆₀@C₁₈₀ is only slightly superior to the C₁₈₀, (2) of the three molecules, the C₆₀ molecule has the best chemical-stability, and the C₆₀@C₁₈₀ molecule has the worst one, (3) with the increase of compressive strain, both the C₆₀ and C₆₀@C₁₈₀ molecules become more chemically active, and (4) when the compressed C₁₈₀ molecule caves in at the loading position(s), its chemical-stability decreases abruptly.     

Production and Characterization of (Al, Fe)-C (Graphite or Fullerene) Composites Prepared by Mechanical Alloying

(Al, Fe)-C_graphite and (Al, Fe)-C_fullerene composites have been prepared by mechanical alloying using ball milling of powders. Consolidation has been achieved by a spark plasma sintering technique (SPS). Results of XRD and TEM indicate that pure fullerene withstands milling. SEM results show homogeneous powders after milling but with different morphologies depending on the specific system. Milling produces a fine mixture of Al or Fe and graphite or fullerene. SPS produces a dense material with a nanocrystalline structure. The sintered samples have a metallic matrix (Al or Fe) with a fine dispersion of AI₄C₃ in the case of Al-C_{( graphiteorfullerene)}, Fe₃,C in the case of Fe-C_(graphite), and fullerene in the case of Fe-C _(fullerene), Hardness measurements show that higher values are obtained in the Al-C_(fullerene), and Fe-C_{(graphite )} specimens.     

Fullerene-incorporation for enhancing the electron beam resist performance for contact hole patterning and filling

The fullerene molecules such as C60 and C70 were incorporated in the commercial positive electron beam resist to investigate the performances for patterning and filling the contact holes at nanometer scale. The sensitivity, process window and contrast of the modified resist were improved, while the toluene dilution degraded the sensitivity. The electron beam dose affected the designed holes dimension, and the adulterated resist could print sub-50 nm holes pattern. We found the small amount (0.01–0.02% w/v) of fullerene molecules very effectively promoted the etch resistance and selectivity under fluoro-containing gases, and minimized the film stress. The etching resistance for C60 and C70 modification could be improved by 65% and 68%, respectively. Together with the fullerene-incorporated resist and the etching processes, the sub-50 nm contact hole could be achieved. In addition, the gap-filling and step coverage capability of titanium nitride into nanometer contact hole with chemical vapor deposition was better than physical vapor deposition.     

Thin fullerene-containing films synthesized by ion beam sputtering of fullerene mixtures with doping additives in vacuum

A new approach to the synthesis of films containing fullerenes and doping elements is described. It is suggested that a cluster mechanism of the target sputtering by accelerated ions makes possible the deposition of fullerenes on a substrate with a certain probability for dopant atoms being introduced into the cavities of fullerene molecules and a higher probability of their occurrence between fullerene molecules. The proposed method has been experimentally implemented by using an Ar⁺ ion beam to sputter C₆₀/C₇₀ fullerene mixtures (synthesized in a plasmachemical reactor at a pressure of 10⁵ Pa) pressed into disk targets with a doping element (Fe, Na, B, Gd, or Se). The ion beam sputtering of dopant-containing fullerene mixtures in a vacuum of ～10^?2 Pa allowed micron-thick films containing C₆₀ and C₇₀ fullerenes and the corresponding dopant element (Fe, Na, B, Gd, or Se) to be grown on quartz substrates.     

Alkali-metal-induced enhancement of hydrogen adsorption in C60 fullerene: an ab Initio study

It is demonstrated that the doping of alkali metal atoms on fullerene, C60, remarkably enhances the molecular hydrogen adsorption capacity of fullerenes, which is higher than that of conventionally known other fullerene complexes. This effect is observed to be more pronounced for sodium than lithium atom. The formation of stable complex forms of a sodium-doped fullerene molecule, Na8C60, and the corresponding hydrogenated species, [Na(H2)6]8C60, with 48 hydrogen molecules has been demonstrated to lead to a hydrogen adsorption density of approximately 9.5 wt %. One of the main factors favoring the interactions involved is attributed to the pronounced charge transfer from the sodium atom to the C60 molecule and electrostatic interaction between the ion and the dihydrogen. The suitability of these complexes for developing fullerene-based hydrogen storage materials is discussed.     

A first-principle investigation into effect of B- and BN-doped $$\hbox {C}_{60}$$ in lowering dehydrogenation of $$\hbox {MXH}_{4}$$MXH4 (where M $$=$$= Na,Li and X $$=$$= Al,B)

The present paper reports the effect of B- and BN-doped \(\hbox {C}_{60}\) as catalysts for lowering the dehydrogenation energy in \(\hbox {MXH}_{4}\) clusters (M = Na and Li, X = Al and B) using density functional calculations. \(\hbox {MXH}_{4}\) interacts strongly with B-doped \(\hbox {C}_{60}\) and weakly with BN-doped \(\hbox {C}_{60}\) in comparison with pure \(\hbox {C}_{60}\) with binding energy 0.56–0.80 and 0.05–0.34 eV, respectively. The hydrogen release energy \((E_{\mathrm{HRE}})\) of \(\hbox {MXH}_{4}\) decreases sharply in the range of 38–49% when adsorbed on B-doped \(\hbox {C}_{60}\); however, with BN-doped \(\hbox {C}_{60}\) the decrease in the \(E_{\mathrm{HRE}}\) varies in the range of 6–20% as compared with pure \(\hbox {MXH}_{4}\) clusters. The hydrogen release energy of second hydrogen atom in \(\hbox {MXH}_{4}\) decreases sharply in the range of 1.7–41% for BN-doped \(\hbox {C}_{60}\) and decreases in the range of 0.2–11.3% for B-doped \(\hbox {C}_{60}\) as compared with pure \(\hbox {MXH}_{4}\) clusters. The results can be explained on the basis of charge transfer within \(\hbox {MXH}_{4}\) cluster and with the doped \(\hbox {C}_{60}\).     

Electro-optical properties,decomposition pathways and the hydrostatic pressure-dependent behaviours of a double-cation hydrogen storage material of $$\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}$$

Electro-optical properties, the decomposition pathways and the pressure-dependent behaviours of \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) have been investigated using a first-principle plane-wave pseudopotential method. \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) is a kind of double-cation borohydride, consisting of distorted tetrahedral anions \([\hbox {Al}(\hbox {BH}_{4})_{4}]^{-}\) and cations \([\hbox {Li}_{4}(\hbox {BH}_{4})]^{3+}\), which obeys the stability criteria of decomposition reactions. Herein, two possible decomposition reactions of the compound are proposed, which release 18 hydrogen molecules (about 12.03 wt%) in the first reaction and 24 hydrogen molecules (about 16.04 wt%) in the second reaction. On increasing the pressure on the structure, the lattice parameter, the volume of unit cell, the quasiparticle band gap and also enthalpy of the system decrease nearly monotonically; therefore, the acceptor levels gradually get filled and the Fermi level shifts upward. Results of computational investigations of the structural, electronic and thermodynamic parameters and their pressure-dependent behaviours indicate that \(\hbox {Al}_{3}\hbox {Li}_{4}(\hbox {BH}_{4})_{13}\) has intriguing properties. Therefore, it would be a very promising material for hydrogen storage technology.     

基体铝合金成分对无压浸渗B4C/Al复合材料微观组织和力学性能的影响

分别选用2024、5056、6061和7075铝合金,采用颗粒级配相同的碳化硼预制体(20%2μm和80%38μm)为增强体,采用无压浸渗法制备4种高体份B4C/Al复合材料(分别对应标记为2M、5M、6M和7M),研究基体合金成分对复合材料的物相组成、微观组织和力学性能的影响。结果表明,4种复合材料均含有A1、B4C、Al3BC、AlB2和富Fe-Mn相,除此之外,2M、5M和7M复合材料还含有Al B10。4种复合材料小颗粒碳化硼聚集区均发生了剧烈的界面反应,生成Al3BC和Al B2。Al B10主要分布于2M、5M和7M复合材料的大颗粒碳化硼周围,并与大颗粒碳化硼连成一体。4种复合材料的洛氏硬度从大到小顺序为2M(45. 7)、7M(43. 1)、5M(41. 8)和6M(40. 02)。2M、5M和7M复合材料内部发现有孔洞存在,导致复合材料弯曲强度和应力均较低。这种效应在7M复合材料中最为明显,其弯曲强度仅为296 MPa。6M复合材料弯曲强度和应变最高,分别为425 MPa和0. 183%,这主要是因为在6M复合材料中,不含Al B10相且残余铝合金相对含量较高。     

Ferromagnetism in C60 polymers: pure carbon or contamination with metallic impurities?

A review of ferromagnetism in C60 polymeric materials synthesized by high pressure high temperature (HPHT) treatment is presented. Analysis of published data proves that the reported ferromagnetism cannot be assigned to polymeric structure in either perfect or defect states. Most recent experimental studies have not confirmed previously reported levels of magnetization in polymeric samples while it appears that ferromagnetism of "magnetic carbon" is preserved above the depolymerization point of any C60 polymer. Identical ferromagnetic properties in some samples of fullerene polymer and graphite like hard carbon phase also show that the effect is most likely not connected to fullerenes at all. Most of the data published previously as an evidence of ferromagnetism in C60 polymers synthesized at HPHT conditions can be explained by contamination with magnetic impurities. Formation of iron carbide (Fe3C) due to reaction of metallic iron with fullerene molecules allows to explain observed Curie temperature of approximately 500 K and levels of magnetization reported for "magnetic carbon".