V. Arumugam
金属学报(英文版)
Acoustic emission (AE) can be used for in situ structural health monitoring of the composite laminates. One of the main issues of AE is to characterize different damage mechanisms from the detected AE signals. In the present work, pure resin and GFRP composites laminates with different stacking sequences such as 0°, 90°, angle ply[±45°], cross-ply [0°/90°] are used to trigger different failure mechanisms when subjected to tensile test with AE monitoring. The study of failure mechanisms is facilitated by the choice of different oriented specimens in which one or two such mechanisms predominate. Range of peak frequencies in each orientation is investigated using FFT analysis. Fast Fourier Transform (FFT) enabled calculating the frequency content of each damage mechanism. Randomly selected hits from each range of peak frequencies for the specimens with different orientations subjected to tensile test with AE monitoring are analyzed using short time FFT (STFFT) analysis. STFFT analysis is used to highlight the possible failure mechanism associated with each signal. The predominance of failure modes in each orientation is useful in the study of discrimination of failure modes in composite laminates from AE data.
关键词:
Composite materials
Acta Chimica Sinica
Passive film formed on 304 stainless steel in 2.5 mol/L H2SO4 solution by using alternating voltage (A. V.) passivation have been investigated by measuring capacitance and photoelectrochemical parameters. The investigation of the effect of measure frequency on the slope of Mott-Schottky curve has been carried out. The photoelectrochemical measurements were consistent with the capacitance measurement. Analysis of the experimental results showed that the passive film formed 304 stainless steel by using A. V. passivation exhibits semiconducting properties. Using the simple model of semiconductor rather than the multi-donor level model can explain satisfactorily the semiconducting behavior of the film formed on 304 stainless steel by using A.V. passivation.
关键词:
A. V. passivation;passive film;semiconducting properties;stainless;steel;model;electrodes
Physics Letters A
We perform first-principles calculations of spin-dependent quantum transport in V doped boron nitride nanotube: the junction of pristine (6, 0) boron nitride nanotube in contact with V doped (6, 0) boron nitride nanotube electrodes. Large tunnel magnetoresistance and perfect spin filtration effect are obtained. The zero bias tunnel magnetoresistance is found to be several thousand percent, it reduces monotonically to zero with a voltage scale of about 0.65 V, and eventually goes to negative values after the bias of 0.65 V. The ratio of spin injection is above 95% till the bias of 0.85 V and is even as large as 99% for the bias from 0.25 eV to 0.55 eV when the magnetic configurations of two electrodes are parallel. The understanding of the spin-dependent nonequilibrium transport is presented by investigating microscopic details of the transmission coefficients. (C) 2008 Elsevier B.V. All rights reserved.
关键词:
first-principles;one-dimensional;tunnel magnetoresistance;spin filter;large magnetoresistance;ferromagnetic-films;sic nanowires;bn;nanotubes;systems;conductance;junctions
Journal of Physics-Condensed Matter
The segregation effects of Nb and V on bcc FeSigma3[110](111) grain boundary cohesion are studied by the first-principles DMol method within the framework of density functional theory. The calculated segregation energy difference between the grain boundary and the corresponding free surface is -0.51 eV (-0.58 eV) for solute Nb (V), which indicates that both Nb and V could enhance the grain boundary cohesion in body-centred-cubic Fe. We found that the chemical effect and the geometry effect of Nb (V) play crucial but opposite roles in determining whether a material is brittle or ductile. The chemical effect is dominant and advantageous for grain boundary cohesion. Also, Nb and V show very different behaviours: in chemical effect, Nb is more conducive to ductility than V; while in the geometry effect, Nb is less conducive to ductility and more conducive to embrittlement than V.
关键词:
first-principles determination;local-density;embrittlement;iron;phosphorus;hydrogen
刘贵仲
,
苏彦庆
,
郭景杰
,
丁宏升
,
贾均
,
傅恒志
材料科学与工艺
doi:10.3969/j.issn.1005-0299.2001.02.015
在基于本课题组建立的熔体组元活度系数计算模型的基础上,计算了Ti-6Al-4V熔体中各组元的活度系数及其蒸气压,推导了判断熔体组元挥发趋势的相对挥发系数β.研究结果表明:在熔体温度低于2 000 K时,铝钛相对挥发系数β(Al:Ti)＞17,铝钒相对挥发系数β(Al:V)＞96,钛钒相对挥发系数β(Ti:V)＞5,即熔炼过程中组元挥发趋势从大到小依次为Al,Ti,V.这说明熔体成分变化主要是由于Al元素的挥发所致.
关键词:
Ti-6Al-4v合金
,
活度系数
,
饱和蒸气压
,
挥发趋势
Thin Solid Films
Single and double layers of tungsten oxide and vanadium oxide thin films have been deposited on In2O3:SnO2 (ITO) glass using the pulsed laser deposition (PLD) technique at a substrate heating temperature of 200 degreesC and in rich oxygen pressure. The structural properties and chemical composition of as-deposited WO3(V) and V2O5(Ti) thin films were analyzed using X-ray diffraction (XRD), Raman spectrum (RS), and X-ray photo-electron spectroscopy (XPS). The as-deposited V2O5 doped WO3 thin film on ITO glass showed an amorphous structure. Highly oriented growth nano-crystalline TiO2 doped V2O5 thin films with polycrystalline orthorhombic structure were successfully synthesized on ITO glass using the scanning laser ablation technique at a deposition temperature as low as 200 degreesC. Cyclic voltammograms, at a sweep rate of 50 mV s(-1), show that long-term degradation was noticed for the as-deposited WO3(V) thin film, and no Ion-term degradation was noticed for the as-deposited double layer WO3(V)/V2O5(Ti) thin film. Durability was verified to 8000 cycles in the voltage range between -1.0 and 1.0 V. It is demonstrated that these double layer WO3(V)/V2O5(Ti) thin films on ITO are good candidates for cathode thin films for rechargeable batteries and electrochromic devices. As the additional top layer of V2O5M) possesses nano-crystalline and c-axis oriented structure, which is suitable for Li-ions transport, the cycle stability and reversibility of WO3(V) films have been improved. Double layer WO3(V)/V2O5(Ti) thin films provide a neutral brownish blue electrochromic color. Therefore, this double layer film maybe suitable for most building applications. (C) 2001 Elsevier Science B.V. All rights reserved.
关键词:
V2O5(Ti);WO3(V) thin films;double layers;pulsed laser deposition;technique;electrochromic properties;chemical-vapor-deposition;vanadium-titanium-oxide;electrical-properties;optical-properties;induced coloration;v2o5;wo3;growth;no2
葛鹏
,
吴欢
,
赵永庆
中国材料进展
doi:10.7502/j.issn.1674-3962.2016.10.06
为了研究钛合金中常用β合金元素Mo、V、Cr等对β相合金化的影响,通过设计制备一系列不同元素含量的Ti-Mo、Ti-V、Ti-Cr二元β型钛合金,分析了含单一合金化元素的β型钛合金的显微组织、硬度及室温拉伸性能.结果发现:随着合金中β稳定元素含量的增加,所有二元合金的晶格常数及晶粒尺寸都呈减小的趋势,其中元素Cr具有最强烈的减小晶格常数效应,而元素Mo对晶粒细化的效果最显著.成分为Ti-xV、Ti-xCr的β相的拉伸强度随元素含量增加的变化规律与硬度变化相似,先减小后增加.Ti-xMo拉伸强度则随元素含量的增加强度升高.元素Cr对β相的强化效果高于Mo和V.
关键词:
钛合金
,
合金元素
,
β相
,
强化
ZHONG Jiaxiang ZHENG Xiuhua XU Zongrui Beijing Institute of Technology
,
Beijing
,
ChinaBAI Dezhong Nei Monggol Machine Works No.2
,
Nei Monggol
,
China Beijing Institute of Technology
,
Beijing 100081
,
China
金属学报(英文版)
Three types of alloy carbides have been observed in tempered steel 4335V:M_3C,M_7C_3 and M_4C_3.The precipitation temperatures are 200—700,400 and 500 ℃ respectively.The com- position,morphologies and distribution patterns of the carbides as well as the relationship be- tween them and as-quenched substructures have been investigated.The influence of the car- bides on the low temperature impact toughness of the steel has also been discussed.
关键词:
steel 4335V
,
null
,
null
