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21.
The formation of aluminum matrix composites fabricated by exothermic dispersion reaction in A1-TiO2-B2O3 system was investigated. The thermal analysis results show that the reactions are spontaneous and exothermic. The Gibbs free energy of α-Al2O3 is the lowest among all the combustion products, followed by TiB2 and Al3Ti. It is noted that when the B2O3/TiO2 mole ratio is below 1, the reaction products are composed of particle-like α-Al2O3, TiB2 and rod-like Al3Ti. The α-Al2O3 crystallites, resulting from the reaction between A1 and TiO2 or B2O3, are segregated at the grain boundaries due to a lower wettability with the matrix. SEM micrographs show that rod-like Al3Ti phase distributes uniformly in the matrix. When the BEO3/TiO2 mole ratio is around 1, the Al3Ti phase almost disappears in the composites, and the distribution of α-Al2O3 particulates is improved evidently. 相似文献
22.
23.
G. Ranzi M. A. Bradford B. Uy 《International journal for numerical methods in engineering》2004,61(5):657-672
The use of the conventional semi-analytical stiffness method in finite element analysis, in which interpolation polynomials are used to develop the stiffness relationships, leads to problems of curvature locking when beam-type elements are developed for composite members with partial interaction between the materials of which it is comprised. The curvature locking phenomenon that occurs for composite steel–concrete members is quite well reported, and the general approach to minimizing the undesirable ramifications of curvature locking has been to use higher-order polynomials with increasing numbers of internal nodes. This paper presents an alternate formulation based on a direct stiffness approach rather than starting from pre-defined interpolation polynomials, and which does not possess the undesirable locking characteristics. The formulation is based on a more general approach for a bi-material composite flexural member, whose constituent materials are joined by elastic shear connection so as to provide partial interaction. The stiffness relationships are derived, and these are applied to a simply supported and a continuous steel–concrete composite beam to demonstrate the efficacy of the method, and in particular its ability to model accurately both very flexible and very stiff shear connection that causes difficulties when implemented in competitive semi-analytical algorithms. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
24.
The eye movements of young and older adults were tracked as they read sentences varying in syntactic complexity. In Experiment 1, cleft object and object relative clause sentences were more difficult to process than cleft subject and subject relative clause sentences; however, older adults made many more regressions, resulting in increased regression path fixation times and total fixation times, than young adults while processing cleft object and object relative clause sentences. In Experiment 2, older adults experienced more difficulty than young adults while reading cleft and relative clause sentences with temporary syntactic ambiguities created by deleting the that complementizers. Regression analyses indicated that readers with smaller working memories need more regressions and longer fixation times to process cleft object and object relative clause sentences. These results suggest that age-associated declines in working memory do affect syntactic processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
25.
Wilhelm Heinrichs 《Journal of scientific computing》1991,6(1):1-19
We introduce a stabilized treatment of spectral methods. The condition number of the spectral systems is highly improved. Elliptic and biharmonic problems are considered. Suitable interpolants in the case of inhomogeneous Dirichlet boundary conditions are presented. For a direct solver the improvements with respect to rounding error propagation are numerically demonstrated. 相似文献
26.
WC对Cu/WC_P复合材料性能及组织的影响 总被引:8,自引:0,他引:8
通过WC含量对WC/Cu复合材料性能的影响,确定了冷压-烧结法制备Cu/WC材料的适宜WC含量为10vol%左右。并就WC对该材料组织和再结晶行为的影响进行了有益的探讨。 相似文献
27.
利用挤压铸造制备氧化铝/锌合金复合材料,在扫描电镜(SEM)上观察复合材料的界面。结果表明,在复合材料中纤维与基体间存在致密界面层,合金元素通过适当的化学反应可改善纤维与基体间的结合;在凝固过程中,纤维/基体界面上的硅在共晶体的共生生长过程中起了领先相作用,导致复合材料的共晶转变是由铝硅共晶转变和锌铝共晶转变两者组成。 相似文献
28.
珠江口盆地开平凹陷油气聚集条件分析 总被引:2,自引:0,他引:2
珠江口盆地自新生代以来,曾先后受到不同方向张应力的作用,造成了不同时期构造体系的交叉叠合.中中新世以来构造运动强烈,并具有东强西弱的特点,对油气的运移与聚集产生了重要影响.开平凹陷的剧烈断裂和断陷活动始于始新世,并在同期沉积了巨厚的文昌组.晚渐新世以后,由于断裂活动非常微弱,在成熟的烃源岩与其上地层之间缺乏有效的油源断层,因而自生自储、近距离运移可能是开平凹陷油气聚集的基本特征.在凹陷内部,因重力滑动和欠压实泥岩共同作用所形成的KPll-1构造带可能是该区最具有油气远景的地区. 相似文献
29.
单轴-平面W型复合锶铁氧体的制备及其吸波特性研究 总被引:3,自引:0,他引:3
用草酸盐共沉淀和微量掺杂法研制六角晶系W型Ni,Zn,Co,Al多元复合锶铁氧体,通过调节Ni2W同Co2W的摩尔比例,可使该种铁氧体易磁化方向从C单轴型向垂于C轴的平面型转化,控制置换锶铁氧体中部分Fe3 的微量掺杂Al3 ,可以调整4πMs值,提高磁晶各向异性场,测试分析了5种不同含Co量的W型复合锶铁氧体粉料涂层的吸波特性,发现其自然共振吸收峰随Co含量增加向低频方向偏移,最高吸收峰可达32.8dB,是适用于电子隐形技术的高品位的微波吸收剂。 相似文献
30.