J. Brnic
,
G. Turkalj and M. Canadija Faculty of Engineering
,
Vukovarska 58
,
51000 Rijeka
,
Croatia
金属学报(英文版)
The optimization problems belong to the family of the most important engineering problems. The objective of this paper is to proposed a very efficient numerical algo- rithm which is involved in an optimal design procedure in the field of viscoplasticity phenomena. Because of the complexity of design procedure, particularly in the field of viscoplas- ticity, the finite element method is used. This method provides a good structural discretization and very efficient mathematical describing of time-rate effects. Accord- ing to the design specifications, which will dictate a limiting design strain, using the proposed algorithm, the design life of the considered structure will be covered. For the justification of the proposed method an example is presented. On the basis of specifications data and environment conditions, an operating pressure of a pressure vessel is obtained.
关键词:
optimal design
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null
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null
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null
马敬翙
,
刘光明
,
曾潮流
,
杜楠
,
赵晴
表面技术
doi:10.3969/j.issn.1001-3660.2006.04.005
采用电化学方法、扫描电镜、能谱分析等技术,研究了常温下镍基高温合金M17和M38G在NaCl溶液和含S2O2-3的NaCl溶液中的腐蚀行为.结果表明,在含质量分数为3.5% NaCl的溶液中,M17和M38G均会遭受严重的点腐蚀;向NaCl溶液(NaCl质量分数为3.5%)添加Na2S2O3(Na2S2O3质量分数为1.5%)后,由于溶液中的S2O2-3在试样表面活性点与Cl-竞争吸附并与H+结合,使两种合金的点蚀均受到抑制;M38G中存在微量的Nb、Ta、Mo等元素使得M38G合金在NaCl溶液中的耐腐蚀性能明显优于M17合金.
关键词:
镍基
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高温合金
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点蚀
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电化学方法
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腐蚀行为
林水东
,
丁马太
功能材料
用示差扫描量热法(DSC)考察了聚丙烯(PP)、聚丙烯/云母(PP/M)和聚丙烯/聚(丙烯-g-甲基丙烯酸甲酯)/云母复合材料(PP/PP-g-MMA/M)的非等温结晶过程.用Avrami方程和Ozawa方程对上述过程进行分析,n、t1/2、F(T)、Tp等参数表明,M和PP-g-MMA,特别是PP-g-MMA的掺入改变了PP的结晶成核和生长机理.用Dobreva方法分析填料的成核活性,ε数值表明,M有较强的成核活性,PP-g-MMA的掺入又进一步增强其成核活性,从而使结晶温度明显提高.Kissinger方法的计算结果表明,添加M可使PP的结晶活化能减小,再添加PP-g-MMA又使PP/M复合体系的结晶活化能进一步减小.
关键词:
聚丙烯
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聚(丙烯-g-甲基丙烯酸甲酯)
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云母
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复合材料
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非等温结晶动力学
Andrej Atrens
材料科学技术（英文）
Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.
关键词:
Stress corrosion cracking
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null
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null
Intermetallics
The phase transformation of alumina formed during oxidation of beta-NiAl coating prepared on M38G alloy by pack cementation was investigated. Oxidation experiments were conducted at 950 degrees C for various times from 2 to 180 min. The phase composition and microstructure of the oxide scales were investigated by using glancing angle XRD, AFM and SEM. The results showed that at the initial oxidation stage needle-like theta-Al2O3 was formed and then it covered the sample surface rapidly. The formation of alpha-Al2O3 grains beneath the theta-Al2O3 layer was favored by depletion of Al in the beta-NiAl coating during oxidation. alpha-Al2O3 preferred growing on the top (ridge) of beta-NiAl grains, which resulted in the formation of net-like alpha-Al2O3 inner layer. With increasing time, theta-Al2O3 transformed to alpha-Al2O3 gradually. After 180 min oxidation, most of alpha-Al2O3 grains transformed into alpha-Al2O3. A mechanism of excessive voids' formation at the oxide/coating interface was also proposed in this paper. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
nickel aluminides, based on NiAl;oxidation;phase transformations;coatings, intermetallic and otherwise;high-temperature oxidation;theta-alpha-al2o3 transformation;behavior;coatings;superalloy;transition;layers
Journal of Magnetism and Magnetic Materials
The electron paramagnetic resonance g factors g(parallel to) and g(perpendicular to) for the trigonal Er3+-V-K centers (where V-K denotes K+ vacancy) in KMF3 (M = Mg and Zn) are theoretically investigated from the perturbation formulas of the g factors for a 4f(11) ion in trigonal symmetry. In these formulas, the contributions to the g factors from the second-order perturbation terms and the admixture of various energy levels are taken into account. In the above trigonal centers, the impurity Er3+ resides in the octahedral M2+ site of both crystals, associated with one V-K in the C-3-axis due to charge compensation. By analyzing their g factors, we find that the impurity Er3+ in both centers would move towards the V-K by an amount DeltaZ along the C-3-axis due to electrostatic attraction. The calculated g factors for the Er3+ centers based on the above displacements DeltaZ show good agreement with the observed values. The validity of the results is discussed. (C) 2004 Elsevier B.V. All rights reserved.
关键词:
electron paramagnetic resonance (EPR);defects and impurities;crystal-field and spin hamiltonians;Er3+;KMF3;(M = Mg and Zn);crystal-field;superposition-model;perovskite kmgf3;conversion;parameters;fluorides;kznf3
蒋彦龙
,
陈国邦
,
甘智华
,
低温物理学报
doi:10.3969/j.issn.1000-3258.2004.02.006
本文开展了高性能G-M型单级脉管制冷机直流抑制和制冷特性实验研究.考察了直流流动对制冷机性能的影响,采用并联布置的双阀逆向型进气结构对直流进行抑制,成功地解决了脉管制冷机的直流问题;此外,深入研究了不同工作模式下,回热器填料布置方式对制冷特性的影响;估算了不同温度位下制冷循环的需气量,对不同压缩机输入功下的双向进气脉管制冷性能进行了研究,采用2kW(RW2)和4kW(CP4000)压缩机驱动时分别获得了18.4K和14.7K的最低制冷温度,在30K的相应制冷量分别为11.5W和29.5W.
关键词:
高性能
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脉冲制冷机
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直流
Materials Science & Engineering C-Biomimetic Materials Sensors and Systems
Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.
关键词:
bamboo;bast fiber;biomimetics;engineering composites
