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31.
Humin Cheng Jiming Ma Zhenguo Zhao Di Qiang Yongxiang Li Xi Yao 《Journal of the American Ceramic Society》1992,75(5):1123-1128
A pure, acicular lead titanate (PbTiO3 ) fine powder with a white color has been prepared by hydrothermal synthesis. It is a new phase of PbTiO3 with I 4 symmetry, cell parameters of a = 12.358 Å and b = 14.541 Å, and a density of 6.80 g.cm−3 . The influences of pH (12.5 to 14.4), Pb/Ti ratio (1.0 to 1.6) in the feedstock, reaction temperature (130° to 230°C), time (0.25 to 4 h), starting materials, and additives on the formation of acicular PbTiO3 under hydrothermal conditions have been investigated. The acicular PbTiO3 with I 4 symmetry, referred to as the PX phase, can be converted to the perovskite-type (PE phase) of PbTiO3 at about 605°C while its acicular morphology is essentially unchanged. The preferable conditions for preparing pure acicular PX-phase PbTiO3 are that the pH is 13.0 to 14.0, Pb/Ti ratio is >1.3, reaction temperature is 170° to 200°C, time is 0.5 to 1.0 h, titanium butoxide (Ti[O(CH2 )3 CH3 ]4 ) is the starting material, and poly(vinyl alcohol) is an additive. The acicular grain of the PX phase is usually less than 100 nm in diameter and more than 1000 nm in length. 相似文献
32.
介绍了利用高炉鼓风机基础实施不易地扩容改造的设计工艺方法,该方法不仅降低了设计、施工、安装费用,而且缩短了施工周期,降低了固定资产投资。 相似文献
33.
随着西北勘测设计研究院(以下简称西北院)勘测总队所承担的黄河龙 ̄青段、白龙江流域等河段前期综合勘测工作的相继结束,拥有2000多名职工的勘测队伍面临着何去何从的重大选择。在此转折关头,勘测总队面对现实,审时度势,抓住机遇,开拓前进,及时转轨变型,制定了本单位发展的战略和方向,使勘测总队由单一勘测业务转变为集勘测与岩土工程施工为一身的新型综合队伍。几年来,经过全体职工的奋发努力,缍获得了1995年 ̄ 相似文献
34.
A Method of Combined SHPB Technique and BP Neural Network to Study Impact Response of Materials 总被引:2,自引:0,他引:2
Abstract: A new method combining the split Hopkinson pressure bar (SHPB) technique with the back-propagation (BP) neural network program is proposed. By this method, the treated strain wave signals become smooth with less noises induced by the transverse inertia. Moreover, the dynamic rate-dependent constitutive behaviour of materials can be identified, without any pre-assumption of a constitutive model. It is found that by taking the experimentally measured data of strain, strain rate and time as 'input' and the corresponding data of stress as 'output' of the BP neural network, the dynamic constitutive behaviour with internal damage or phase transformation evolution is easy to be identified, where the time could represent either the internal damage evolution or phase transformation process accompanied with the deformation process. It is emphasised that the data learnt by the BP neural network must include both loading and unloading processes, if the whole loading and unloading response is to be correctly predicted. The comparisons between the predictions and experimental results are in good agreement for both polyamide (PA) polymer (as an example of nonlinear viscoelastic materials) and Ti–Ni alloy (as an example of superelastic materials with stress-induced phase transformation). 相似文献
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In order to study the influence of cerium ion implantation on the aqueous corrosion behavior of zircaloy-4, specimens were implanted by cerium ions with a fluence range from 1×1016 to 1×1017 ions/cm2 at maximum 150°C, using MEVVA source at an extracted voltage of 40 kV. The valence and elements penetration distribution of the surface layer were analyzed by X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES) respectively. Glancing angle X-ray diffraction (GAXRD) was employed to examine the phase transformation due to the cerium ion implantation in the oxide films. Three-sweep potentiodynamic polarization measurement was employed to value the aqueous corrosion resistance of zircaloy-4 in a 1 N H2SO4 solution. It was found that a significant improvement in the aqueous corrosion behavior of zircaloy-4 implanted with cerium ions compared with that of the as-received zircaloy-4. The improvement effect will declined with raising the implantation fluence. The bigger is the fluence, the less is the improvement. Finally, the mechanism of the corrosion behavior of the cerium-implanted zircaloy-4 is discussed. 相似文献
37.
G.P. Potirniche 《Engineering Fracture Mechanics》2003,70(13):1623-1643
Crack tip plastic zone sizes and crack tip opening displacements (CTOD) for stationary microstructurally small cracks are calculated using the finite element method. To simulate the plastic deformation occurring at the crack tip, a two-dimensional small strain constitutive relationship from single crystal plasticity theory is implemented in the finite element code ANSYS as a user-defined plasticity subroutine. Small cracks are modeled in both single grains and multiple grains, and different crystallographic conditions are considered. The computed plastic zone sizes and CTOD are compared with those found using conventional isotropic plasticity theory, and significant differences are observed. 相似文献
38.
SKYPE在远程英语教学方面的实时应用 总被引:2,自引:0,他引:2
SKYPE系统是目前世界上最流行的互联网远程视频、音频、文字实时交互平台,其音频、视频传播实时非常清晰,这对将远程教育拓展到家庭,特别是对推动远程英语教育的广泛性和普遍性能够起到很大的作用,本文就该平台的基本功能和性能做了介绍,并在远程英语教育方面的应用提出了实践的方法。 相似文献
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本文从理想材料轴对称弹塑性问题的所有基本方程出发,研究了全塑性时轴对称空间问题的塑性应变分布规律和应力场,并推导了控制应力分布的定解方程,给出了全塑性轴对称问题的通用解法。 相似文献