热带粗轧机组调宽工艺中数学模型的建立

采用铅作为模拟材料，对热带粗轧机组平辊立轧－－平轧调宽的变形规律进行了实验研究，简要分析了立轧时的“狗骨”行为和随后平轧时宽度变化行为与来料厚度，宽度、轧辊直径和压下量的关系，并建立了新的数学模型。     

Microstructures and improved wear resistance of 3D needled C/SiC composites with graphite filler

Three-dimensional (3D) needled carbon/carbon (C/C) composites with a lowest porosity of 15.6% were achieved after 1 cycle of impregnation by phenolic resin slurry containing graphite filler, hot-pressing curing and pyrolysis. Carbon/silicon carbide (C/SiC) composites were obtained by liquid silicon infiltrating C/C composites. The aim was to incorporate cost effectiveness and excellent performance of C/SiC braking material. Using filler content not exceeding 30 wt% in the slurry promised undamaged C/C segments in C/SiC composites. The linear wear rate of C/SiC using 30 wt% filler was 0.33 μm side⁻¹ cycle⁻¹ and displayed a fourfold decrease; its weight wear rate was 2.46 mg side⁻¹ cycle⁻¹ and minus 171%, compared with the previously reported values of C/SiC without filler, at a braking velocity of 28 m/s. Its friction coefficients and friction stability coefficients appeared relative insensitive to changes in braking velocities and displayed higher values at high braking velocities compared with the previous values.     

Simulated three-dimensional transient temperature field during aircraft braking for C/SiC composite brake disc

In the present work, a theoretical model of three-dimensional transient temperature field for C/SiC composite brake discs was established by adopting a finite element method according to the theory of energy transformation and transportation. The variation regularities of transient temperature field and internal temperature gradient of the brake discs were obtained. The effects of initial velocity, deceleration and friction coefficient on the highest temperature of the brake discs were also discussed. The heat energy was mainly concentrated on the layer of friction surfaces. The highest temperature of the brake discs under normal landing, overload landing, and rejected take-off landing condition were 869.7 K, 1037.4 K and 1440.3 K, respectively. Furthermore, the highest temperature of the brake discs increased with the increase of the initial velocity and friction coefficient, but decreased with the increase of deceleration. Comparing simulation predictions with experimental results, it is found that the three-dimensional transient temperature field model was valid and reasonable.     

基于ANSYS的交流接触器电磁机构的三维有限元分析

本文以CJ20-25型交流接触器为例,借助大型有限元分析软件ANSYS,对其双E型电磁机构建立了三维有限元模型,得到了磁场分布图,完成了动态吸力特性和磁链的计算,并将结果与实测数据进行了比较和分析。     

Calcium antagonistic effects of Bambusa Rigida investigated by Ca and its protection on myocardial ischemia of rats

An investigation was conducted using 45Ca as a radioactive tracer to evaluate calcium antagonistic effects of several extracts from Bambusa Rigida in living rats. The relationship between the flavonoid and saccharide contents of Bambusa Rigida and calcium antagonistic effects were also analyzed. The protective effects of the alkali extracts ofBambusa Rigida on myocardial ischemia were investigated in living rats. The results indicated that the alkali extracts of Bambusa Rigida had a prominent influence on Ca2 influx and efflux in the isolated rat aorta and heart, as they could obviously block 45Ca entering into cells and stimulate efflux of intracellular Ca2 . Moreover, the alkali extracts of Bambusa Rigida had favorable protective effects on myocardial ischemia induced either by isoproterenol injection (ISO) or by the ligation of coronary artery. These results implied that the Bambusa Rigida had attractive potential for the treatment of heart, cerebrovascular and other diseases. However, the conclusion that whether the flavonoid or saccharide in Bambusa Rigida affected the calcium antagonistic effects and Ca2 channels or not was hard to make within the results of the investigation.     

层状SiC/BN陶瓷的制备及抗冲击性能

为发展高性能结构功能一体化的新型陶瓷装甲防护材料,采用流延法结合热压烧结法制备了不同结构设计的层状SiC/BN陶瓷,研究了材料的烧结特性、显微结构、力学性能及抗冲击性能.结果表明:层状结构设计可以实现陶瓷材料的强韧化效果,其失效模式为非脆性断裂,保持结构完整性的能力明显提升;弯曲强度410 MPa,断裂韧性7.6 MP...     

Cyclic Oxidation Behavior of the Ti–6Al–4V Alloy

The cyclic oxidation behavior of the Ti–6Al–4V alloy has been studied under heating and cooling conditions within a temperature range from 550 to 850 °C in air for up to 12 cycles. The mass changes, phase, surface morphologies, cross-sectional morphologies and element distribution of the oxide scales after cyclic oxidation were investigated using electronic microbalance, X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The results show that the rate of oxidation was close to zero at 550 °C, obeyed parabolic and linear law at 650 and 850 °C, respectively, while at 750 °C, parabolic—linear law dominated. The double oxide scales formed on surface of the Ti–6Al–4V alloy consisted of an inner layer of TiO₂ and an outer layer of Al₂O₃, and the thickness of oxide scales increased with an increasing oxidation temperature. At 750 and 850 °C, the cyclic oxidation resistance deteriorated owing to the formation of voids, cracks and the spallation of the oxide scales.     

Oxidation resistance and thermal shock properties of self-healing SiCN/borosilicate glass-B4C-Al2O3 coatings for C/C aircraft brake materials

SiCN/borosilicate glass-B₄C-Al₂O₃ coating was deposited on carbon fiber-reinforced carbon matrix (C/C) brake materials to protect them from oxidation. Microstructural analysis revealed that the coating was dense and uniform. Fabricated coating showed excellent oxidation resistance and significantly low weight losses after oxidation in dry air for 10?h than SiCN/borosilicate glass-B₄C coated samples (ca. 0.12%, 0.51%, and 0.29% at 700, 800, and 900?°C, respectively). B₄C is believed to react with the oxygen diffused into the coating to produce B₂O₃, which could heal cracks of the coating and improve its self-sealing ability and oxidation resistance. The Al₂O₃ present in the outer glass layer is believed to inhibit volatilization of B₂O₃, thereby reducing weight losses in air. Fabricated coating also possessed excellent oxidation resistance under fresh and sea water conditions, with cracks and pores generated during oxidization process being effectively healed. Prepared coating materials showed excellent thermal shock resistances after 50 thermal shock cycles, with weight losses being as low as 0.23%.     

新时期城市总体规划实施评估的框架与方法——以武汉市城市总体规划(2010-2020年)实施评估为例

总体规划实施评估作为优化规划编制和实施机制的重要环节,是完善总体规划制度和促进总体规划改革的重要内容.在当前城市转型和规划改革双重背景下,评估工作具有复杂性.结合《武汉市城市总体规划 (2010-2020年)实施评估》实践,从终期评估特点出发,对评估的作用、内容框架、技术方法及若干趋势等进行了探讨,提出新时期总体规划实施评估要在规划内容、实施状况和实施效果评价的基础上,加强对城市问题和运行质量的诊断,关注实施过程,并从未来适应性出发做出趋势研判,为总体规划调整修编提供支撑,同时还要加强新方法新技术的运用,提高对城市空间特征和运行过程的解析能力.