Model of Viscoplasticity for Transversely Isotropic Inelastically Compressible Solids

A transversely isotropic, viscoplasticity model is formulated as an extension of Bodner's model. Account is made of inelastic deformation that can occur in strongly anisotropic materials under hydrostatic stress. The extended model retains the simplicity of the Bodner model, particularly in the ease with which the material constants are determined. Although the proposed model is based on a scalar state variable, it is capable of representing material anisotropy under the assertion that history-induced anisotropy can be ignored relative to strong initial anisotropy. Physical limitations on the material parameters are identified and discussed. The model is applied to a W∕Cu metal matrix composite; characterization is made using off-axis tensile data generated at NASA Glenn Research Center.     

碳纳米管的性能与应用研究

随着对碳纳米管研究的不断深入,对碳纳米管的应用研究也吸引了越来越多的学者.文章综述了碳纳米管的独特性质、当前的研究状况并对其应用前景进行了广泛的探索.详细介绍了碳纳米管的力学、电学、吸附及光学等性质,并讨论了其在纳米机械、场发射、电磁吸收、光吸收等领域的应用.研究表明:碳纳米管在众多领域具有广泛的应用前景.     

碳纳米管对镁锌合金组织及性能的影响

采用钟罩浸块铸造法制备了不同碳纳米管含量的镁锌合金铸锭,经热挤压后制备出不同碳纳米管含量变形镁锌合金,研究碳纳米管作为增强材料加入到不含铝的镁锌二元合金中,对其组织和性能产生的影响。利用光学显微镜、扫描电镜及拉伸强度实验机对其显微组织形态及力学性能进行了分析。结果表明,碳纳米管的加入能够显著细化合金铸锭的晶粒起到了细化树枝晶二次枝晶臂间距和转变晶体生长方式的作用,且经过热挤压变形后组织变得更加均匀细小,具有细晶组织;碳纳米管对热挤压镁锌合金的力学性能有增强作用,提高了镁锌合金的抗拉强度、屈服强度、延伸率,当加入量为1.0%时,分别达到最大值219.740,215.969 MPa,27%,其中以延伸率的提高最为显著,抗拉强度和屈服强度值趋于稳定,可得碳纳米管加入到镁锌合金中,起到了较好的复合效果,对晶粒和晶界起到细化和强化的作用,使得该材料具有较高塑形的同时没有降低其强度;合金的断裂特征为典型韧性断裂,有较深的圆形韧窝和撕裂棱组成,碳纳米管与基体合金结合紧密,在拉伸断口处的白色须状物质即为表面被基体合金包覆的碳纳米管。     

Thermal Postbuckling of Laminated Composite Plates with Temperature Dependent Properties

The paper deals with the theoretical investigation of the postbuckling of laminated composite rectangular plates subjected to uniform in-plane temperature. An analytical method based on Chebyshev polynomial is employed. The formulation is based on Reissner–Mindlin plate theory and von Kármán nonlinear kinematics. The resulting nonlinear coupled differential equations are linearized using quadratic extrapolation technique. Double Chebyshev finite series is used to discretize the differential equations. An incremental iterative approach is employed for the solution. The effects of temperature dependent mechanical and thermal properties on the limiting/critical temperature and the postbuckling response are studied. The numerical results for different boundary conditions and lamination schemes are presented. Analysis results indicate that temperature dependent properties reduce the critical/limiting temperature and postbuckling strength.     

纳米碳管铝基复合材料组织与性能的研究

试验采用搅拌铸造法制备了纳米碳管增强铝基复合材料,对其显微组织、硬度、抗拉强度和电阻率进行了研究.结果表明:纳米碳管的加入能够细化复合材料晶粒,表面镀铜后可以抑制基体与增强体之间的界面反应,避免脆性碳化物的生成;复合材料的硬度和抗拉强度随着纳米碳管加入量的增加先增加后减小,纳米碳管的质量分数为1.0%时,达到最大值,与基体相比分别增加了34.8%和34.4%;纳米碳管的加入对基体的导电性影响不大.     

Homogenization for Dispersion and Reduction in Length of Carbon Nanotubes

An important aspect that limits the use of carbon nanotubes (CNTs) is the difficulty in obtaining homogeneously dispersed CNTs of uniform length. Hence, homogenization of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) was carried out using bullet blender and the dispersion behavior was compared with that of ultrasonication. 1% sodium dodecyl sulphate (SDS), Triton-x-100 and polyethylene glycol 4000 were used as dispersing agents during homogenization. The dispersed CNTs were studied using transmission electron microscopy, ImageJ and Raman spectroscopy. Though dispersion and reduction in length of MWCNTs were observed both with ultrasonication and homogenization, lowest length range with about 75% reduction in polydispersity index was obtained on homogenization. Longer time of ultrasonication resulted in damage to small MWCNTs. Well dispersed and shorter MWCNTs were obtained with Triton-x-100 while reduction in length was minimum with SDS. SWCNTs of less than 1 μm length could be obtained by homogenization with Triton-x-100.     

Nanomechanics Modeling and Simulation of Carbon Nanotubes

Carbon nanotubes (CNTs) have been perceived as having a great potential in nanoelectronic and nanomechanical devices. Recent advances of modeling and simulation at the nanoscale have led to a better understanding of the mechanical behaviors of carbon nanotubes. The modeling efforts incorporate atomic features into the continuum or structural mechanics theories, and the numerical simulations feature quantum mechanical approach and classical molecular dynamics. Multiscale and multiphysics modeling and simulation tools have also been developed to effectively bridge the different lengths and time scales, and to link basic scientific research with engineering application. The general approaches of the theoretical and numerical nanomechanics of CNTs are briefly reviewed. This paper is not intended to be a comprehensive review, but to introduce readers (especially those with traditional civil engineering or engineering mechanics backgrounds) to the new, interdisciplinary, or emerging fields in engineering mechanics, in this case the rapidly growing frontier of nanomechanics through the example of carbon nanotubes.     

Transversal Flux Scanning Induction Heating of Magnetic Nonlinear Steel Sheets With Temperature Dependent Properties

This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of steel properties.The decrease of the non-uniformity of the transversal profile of sheet heating as effect of the magnetic or electromagnetic screening of the sheet lateral sides was proved.     

Synthesis and Characterization of Carbon Nanotubes Doped Hydroxyapatite Nanoceramic for Orthopedic Applications

Nano-sized bioceramic hydroxyapatite (HAp) reinforced with carbon nanotubes (CNT) is synthesized using the sol–gel technique with phosphoric acid and calcium nitrate tetrahydrate as a phosphorous and calcium precursor, respectively. The ‘as synthesized’ nanocomposite powder is characterized for phase and structural analysis using X-ray diffractometry, FTIR and Raman spectroscopy. The morphological analysis of HAp/CNT nanocomposite is done using field emission scanning electron microscopy. The tribological properties including wear rate and coefficient of friction are done by coating HAp and HAp/CNT nanocomposite on implant material (SS 316L) using spin coating technique. The wear is reduced by 24.57% for HAp-coated SS316L and 29.6% for HAp-5% CNT-coated SS316 substrate. The addition of CNT in HAp matrix leads to lowering of the coefficient of friction.     

活性炭表面性质对Pd/C常温氧化CO的影响

采用等体积浸渍法制备了活性炭负载Pd催化剂(Pd/C),通过正交实验研究了活性炭的种类、催化剂的制备条件等对活性炭负载钯催化剂上CO氧化性能的影响,得到了最优的制备条件。并通过N2吸附、程序升温脱附(TPD)、程序升温还原(H2-TPR)和透射电镜(TEM)等对催化剂进行了表征。正交实验极差分析表明制备各因素对催化剂氧化CO活性影响的次序为:还原剂>活性炭>还原剂用量>还原温度>还原溶pH值。催化剂表征结果表明活性炭的比表面积和孔径分布不是决定Pd/C催化剂性能的关键因素,活性炭的种类、表面组成和性质对催化剂的性能有显著的影响。其中椰壳炭(AC1)表面羧基的活性较高,同时具有较强的表面碱性,有利于活性金属Pd在载体表面的分散,并提高了Pd与载体之间的相互作用,从而使催化剂具有较高的CO氧化性能。提高Pd的担载量,可显著提高催化剂稳定性。以乙二醇作为还原剂,在pH=10,还原温度为60℃的条件下所制备的0.5%Pd/AC催化剂,在反应温度20℃时连续反应120 h仍可保持CO的全转化。     

Effect of Multiwalled Carbon Nanotubes on the Thermal Conductivity and Porosity Characteristics of Blast Furnace Carbon Refractories

Different amounts of carbon nanotubes (CNTs) (0–5 mass pct) containing carbon refractory specimens for a blast furnace were prepared and coked for 3 hours at 1473 K (1200 °C) and 1673 K (1400 °C). The thermal conductivity and porosity characteristics of the coked specimens were evaluated using the flash diffusivity technique and mercury porosimetry, respectively. It was found that CNTs acted as carbon source, and most of them were consumed during coking. With the increase of CNT content, the aggregation of CNTs became more severe, the amount of SiC whiskers formed increased and their aspect ratio became larger, and the SiC whiskers tended to be distributed nonhomogeneously. The thermal conductivity of a 4 mass pct CNT containing a carbon specimen was highest because of the contributions of SiC and residual CNTs. The porosity characteristics of a 0.5 mass pct CNT containing a carbon specimen was best because of the uniform filling of SiC whiskers. The excessive addition of CNTs degraded the porosity characteristics because of the severe aggregation of CNTs.     

Microstructure and Properties of Zircon-Added Carbon Refractories for Blast Furnace

Microstructure and properties of zircon-added carbon refractory specimens for blast furnace (BF) were investigated with the aid of X-ray diffraction (XRD), a scanning electron microscope (SEM), energy-dispersive X-ray, mercury porosimetry, and a laser thermal conductivity (TC) meter. Additives could influence the matrix structures and improve the properties of specimens. With the increase of zircon powder content, the amount of SiC whiskers formed increased and their aspect ratio became larger, and the SiC whiskers tended to be distributed homogeneously. Zircon powder additions decreased the mean pore diameter and increased?<1-??m pore volume by filling in pores via SiC, improved the TC and the cold crushing strength (CCS) due to the in-situ formation of the more well-developed SiC whiskers with high TC, and significantly reduced the molten iron attack to carbon specimens.     

Considering Carbon Capture and Storage for Energy Generation from Municipal Solid Waste

Modern waste management practices encourage the recovery of energy from municipal solid waste after efforts to reduce, reuse, and recycle appropriate materials. Energy can be recovered through direct mass burn in a waste-to-energy (WTE) facility or through the collection and combustion of biogas generated in sanitary landfills. Many comparisons have been made although rarely using best practice assumptions for both technologies; WTE proponents tend to assume low collection efficiency while landfill proponents tend to assume low electrical conversion efficiency. In general, WTE plants can be considered to have a better environmental performance (reduced emissions) with landfill having lower total costs (social and environmental). Both strategies have similar costs when considering 77% collection efficiency and a high efficiency (30% electrical conversion) WTE plant that displaces electricity from coal. The introduction of carbon capture and storage (CCS) technologies to waste management changes the landscape by increasing the capital costs and improving the environmental performance. The air emissions are significantly reduced, practically eliminated with oxygen combustion, as the capture of CO2 requires significant flue gas scrubbing. The introduction of CCS results in a net environmental benefit for WTE plants with a turnaround electricity price of $7/MWh, as compared to landfill gas with capture. The largest environmental cost for WTE plants is the classification of fly ash as chemical waste, which is reduced with oxygen combustion. The net cost of capturing CO2 from WTE facilities is estimated at $39/t CO2, one-third of the cost of CO2 capture from landfills.     

回火温度对低碳贝氏体钢Q590组织和冲击性能的影响

利用热处理炉进行不同温度区间Q590 低碳贝氏体钢回火试验.结果表明:试验钢在300～350℃回火温度区间产生回火脆性,造成冲击性能偏差;随着回火温度的升高,冲击性能又明显得到改善.分析认为:M-A 岛分解在250～550℃回火温度区间发生,即从250℃左右开始,在300～350℃之间数量多、尺寸大,且沿晶界分布,是导...     

Effect of Carbon Aggregates on the Properties of Carbon Refractories for a Blast Furnace

The effect of carbon aggregates on the carbon refractory properties for a blast furnace was studied with X-ray diffraction (XRD), scanning electron microscopy (SEM), an energy-dispersive X-ray, mercury porosimetry, a resistivity instrument, and a laser thermal conductivity meter. The results showed that the microporous structure of a sample was determined by the amount of β-SiC whiskers. The thermal conductivity was controlled by the thermal conductivity of the corresponding carbon aggregate, and the alkali and molten-iron attack was decided mainly by the pore and the graphitization degree of aggregate, respectively. For samples using calcined anthracites as aggregates, the microporous structure became worse, the thermal conductivity increased, and the molten-iron as well as the alkali attack became more severe with an increase in the anthracite calcining temperature. For all samples, microcrystalline graphite possessed the best microporous structure and the least alkali and molten-iron attack, whereas the graphite electrode scraps had the highest thermal conductivity and the most severe alkali and molten-iron attack.     

碳对稀土重轨钢组织和性能的影响

通过真空感应炉模拟实验,结合金相分析和性能测定.研究碳对于稀土重轨钢微观组织、冲击韧性和强度等的影响作用.研究表明,随着碳含量的增加,稀土重轨钢的奥氏体晶粒尺寸和珠光体片层间距逐渐增大,屈服强度和抗拉强度逐渐增大,冲击韧性则逐渐减小.在本实验条件下,将稀土重轨钢的碳含量控制在0.600%～0.650%之间,对于强度的损失并不大,但对于改善冲击韧性具有显著效果.     

Formation of Carbon Nanotubes and Microsilica during the Production of Crystalline Silicon in Three-Phase Ore-Thermal Furnaces

Russian Journal of Non-Ferrous Metals - The annually generated waste of silicon production in Irkutsk oblast equals 20 000 t/year, and the volume of waste accumulated in the three sludge...