关键词： 链条炉   机械搅动  

摘要： 对链条热水锅炉炉排增加机械搅动装置后,对床层燃烧影响状况进行分析,得出结论。链条炉排增加机械搅动装置后,可以提高煤的燃烧效率。

关键词： 农业   动力机械   更新发展  

摘要： 农业动力机械在农业生产中起到了一个重要的作用,降低农业生产中对劳动力、物力的要求,提高了农业生产力。农业动力机械的不断更新使农业得到了良好的发展,提高了农业生产效率,农业动力机械更新是农业技术的一个重要环节。文中对影响农业动力机械更新的各种因素进行探讨,探讨农业动力机械更新的发展方向,为以后的农业技术推广工作提供依据。

关键词： 并联机械腿   伺服电机   动力学分析   Lagrange方程   峰值预估模型  

摘要： 提出了一种结构紧凑、承载能力大、转动解耦性好、运动速度和加速度大的3自由度并联机械腿。为了对其进行驱动参数分析,对机械腿进行了动力学建模,并基于动力学模型进行了伺服电机峰值预估。首先,分析了腿部机构各构件的运动参数,采用Lagrange方程建立了动力学模型,得出了机构驱动力的显式解;接着,在机构动力学模型的基础上,建立了伺服电机驱动转速和驱动力矩的峰值预估模型;最后,通过给定一组结构参数和运动轨迹函数,得出了伺服电机驱动转速和驱动力矩随时间变化曲线,得到了机构的动力学特性,并验证了峰值预估模型的正确性。计算表明,3个伺服电机驱动转速的峰值分别为Nx=19r/s、Ny=17r/s、Nw=27r/s;3个伺服电机驱动力矩的峰值分别为εx=5.8N.m、εy=3.1N.m、εw=4.4N.m。

关键词： Fenestrated endovascular repair   AAA   FSI  

摘要： Fenestrated endovascular aneurysm repair (f-EVAR) stent grafts offer an alternative treatment for conventional open heart surgery for patients with juxsta-renal Abdominal Aortic Aneurysms (AAA) that are unsuitable for the common infrarenal endovascular aneurysms repair (EVAR) procedure. The f-EVAR endograft includes branched stent grafts fixed to the aortic endograft main body via designated strengthened fenestrations. Repetitive stresses activated upon the endograft by the pulsatile flow might cause detachment or fracture of branching. Thus, investigation of the flow forces and stresses on the graft may help minimize complications and improve the endograft design. The present work investigates the flow and stress fields of the fenestrated endograft configuration using a fluid structure interaction (FSI) model in order to evaluate risks for graft fracture or detachments. The results show that the f-EVAR dramatically improves the aortic and iliac flow and that elevated cyclic stresses are found at the graft's bifurcation and branches' connections. (c) 2012 Elsevier Masson SAS. All rights reserved.

关键词： Solid Oxide Fuel Cell   Cermet Ni-YSZ   Redox stability   Kinetics   Modelling  

摘要： The 'redox' tolerance of a typical anode supported cell was evaluated for three temperatures of re-oxidation. For this purpose, an experimental work has been coupled to a modelling approach to estimate the risk of electrolyte failure during re-oxidation. A special attention has been paid to take into account both (i) the heterogeneity of oxidation and (ii) the cermet visco-plasticity in operation. Data required for the simulations - i.e. the oxidation kinetics rates, the cermet expansions and Young's modulus - were determined at T = 600, 700 and 800 degrees C. It has been found that the activation energy related to the kinetics of re-oxidation encounters a modification at high temperature (700-750 degrees C). This modification has been ascribed to a transition from a homogeneous oxidation process to a heterogeneous one. Local X-ray measurements have confirmed that an oxidation gradient in the cermet arises at T = 800 degrees C. Mechanical analysis has shown that the presence of an oxidised front at T = 800 degrees C: strongly impacts the cell 'redox' tolerance. Indeed, this phenomenon induces a significant cell bending, which adds a compressive stress component to the thin electrolyte. simulations have been carried out to determine both critical degree of oxidation and durations before electrolyte cracking. The effect of the cermet creep during operation on the cell 'redox' tolerance is also discussed. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词： SWCNT   SWCNT bundle   MWCNT   Mechanical properties   MD simulation   Fracture  

摘要： Carbon nanotubes have caught tremendous attention of the researchers during the last decade due to their excellent mechanical, electrical, optical and thermal properties. The exploitation of these fibers as reinforcing agents in making strong fiber composites has been a primary research topic in the recent investigations on composite materials. Although the theoretical results are rather optimistic, the goal of achieving high strength of the carbon nanotube composites is still not satisfactorily realized. We report here a comparative study of the mechanical properties of single-walled, multi-walled and bundle of single-walled carbon nanotubes. Their mechanical behavior is investigated by molecular dynamics simulation, considering Brenner's second generation reactive empirical bond order interatomic potential between the carbon atoms making a tube. For a long range interaction, we have defined a weak van der Waals force which acts between different layers of a multi-walled tube or between different tubes of a bundle. Samples of three isolated armchair single-wall carbon nanotubes of different diameters, a multi-wall armchair carbon nanotube and finally a bundle of three armchair single-walled nanotubes of same diameter are taken. Their fracture pattern and buckling behavior are modeled and compared. Significant changes are observed in the mechanical properties of the samples of different types of carbon nanotubes which arise due to the interaction between the shells of a multi-walled tube or the tubes in a bundle.

关键词： Andosol   Temporal changes   Air and water conductivity   Precompression stress  

摘要： Soil physical properties continuously change as a result of wetting and drying cycles (WD), soil tillage and grazing events. In order to define sustainable grazing management, it is necessary to determine how the soil responds during and after applied external stresses. This is relevant in southern Chile where pastures are the main livestock feed throughout the course of the year and Andosols are exposed to great mechanical stresses by a wide range of soil water contents. Therefore, the purpose of this paper was to illustrate the effect of grazing. considering two grazing intensities in the winter: 50 and 200 cows ha(-1), on the temporal changes of structure-dependent properties of an Andosol in southern Chile. In order to characterize the impact of grazing, 15 soil samplings (5-10 cm depths) were conducted over a 2 year period. The penetration resistance (PR) and soil water content were determined in the field. Air capacity (AC), air (k(l)) and saturated hydraulic (k(s)) conductivity, precompression stress (Pc), and aggregate strength (AS) were measured. Changes in the soil mechanical stability and pore functions were observed as a consequence of grazing events and WD cycles, indicating that the structure-dependent properties are dynamic. Animal trampling induced an increase in PR;however, the increase in soil mechanical strength may not affect root growth, considering the changes in time of the PR and the specific properties of Andosol (e.g. bulk density <0.9 Mg m(-3)). Temporal variations in Pc did not exceed critical values for root growth even under high grazing intensities, indicating that the soil recuperates after the impact of trampling during grazing. The air capacity/conductivity values measured in our study reached critical values for gas exchange as a consequence of animal trampling;however, the Andosol showed its ability to recuperate its integral pore functionality. Finally, in spite of the low bulk density of the Andosol, the increasing grazing inten

关键词： STEEL metallurgy   POWDER metallurgy   NANOSTRUCTURED materials   TENSILE strength   ISOTHERMAL processes   HEAT treatment  

摘要： A PM approach is investigated in the context of extremely fine low temperature bainitic steels with a reasonable combination of ultimate tensile strength and uniform elongation. The strategy consists of three steps. First, ball milling is used for mechanical alloying and to create a large density of interfaces prior to sintering. In the second step, spark plasma sintering is used as a rapid consolidation process to retain a very fine and homogeneous structure after sintering. The isothermal heat treatment which leads to bainite can then be done at a low austenitisation temperature (860 degrees C) for a few minutes, leading to a small initial austenite grain size. A fine grain size promotes the rapid transformation of the austenite into bainite. The characteristics of a nanostructured Fe-Ni-C bainitic steel obtained after mechanical alloying and nanostructuring of the powder, spark plasma sintering and final heat treatment are reported.

关键词： Glasses,metallic   Internal friction   Thermal properties   Defects: theory  

摘要： Structural relaxation in Cu46Zr45Al7Dy2, Ti40Zr25Ni8Cu9Be18 and Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit 1) bulk metallic glasses has been studied by mechanical spectroscopy during annealing below the glass transition temperature T-g. Structural relaxation in bulk metallic glasses leads to an increase of the storage modulus G' and a decrease of the loss factor tan delta, which are observed after an incubation time. Kinetics of this phenomenon can be well described by a stretched exponential, similar to the Kohlrausch -Williams-Watts (KWW) equation used to fit differential scanning calorimetry (DSC) experiments. In the various investigated bulk metallic glasses the stretching exponent beta(KWW) does not depend on annealing temperature implying therefore that this exponent beta(KWW) is nearly independent of the microstructure. Decrease in the loss factor is due to a decrease in the atomic mobility. Various models have been proposed in the literature to describe this evolution: decrease in the free volume, decrease in the liquid-like regions or decrease in the defect concentration (flow defects or quasi-point defects). Present results are discussed using this concept of defect. In any case it corresponds to an increase of the short range order during annealing below the glass transition temperature T-g. (C) 2012 Elsevier Ltd. All rights reserved.