关键词： Anisotropic mechanical property   Graphene   Young's modulus   Fracture   Molecular dynamics  

摘要： Anisotropic mechanical properties are observed for a sheet of graphene along different load directions. The anisotropic mechanical properties are attributed to the hexagonal structure of the unit cells of the graphene. Under the same tensile loads, the edge bonds bear larger load in the longitudinal mode (LM) than in the transverse mode (TM), which causes fracture sooner in LM than in TM. The Young's modulus and the third order elastic modulus for the LM are slightly larger than that for the TM. Simulation also demonstrates that, for both LM and TM, the loading and unloading stress-strain response curves overlap as long as the graphene is unloaded before the fracture point. This confirms that graphene sustains complete elastic and reversible deformation in the elongation process. (C) 2009 Elsevier B.V. All rights reserved.

关键词： 工程船舶   动力机械   状态监测   故障诊断  

摘要： 针对工程船舶动力机械运行特点,详述工程船舶动力机械状态监测和故障诊断研究的意义,介绍国内外常见船舶动力机械状态监测与故障诊断的方法和现状,并指出工程船舶动力机械状态监测和故障诊断技术的发展趋势和研究热点。

关键词： 摆线凸轮   力学模型   动力学  

摘要： 对摆线凸轮—从动杆机构,提出线性及非线性模型,并应用拉氏变换分析了该系统的动力学问题,为进行现代化设计提供了正确的理论科学依据。

关键词： MOLECULAR dynamics   HYDROGEN   GRAPHENE   MATERIALS -- Mechanical properties   SIMULATION methods & models   NANOELECTROMECHANICAL systems   CHEMICAL bonds   MICROFABRICATION  

摘要： Molecular dynamics simulations have been performed to investigate the mechanical properties of hydrogen functionalized graphene for H-coverages spanning the entire range from graphene (H-0%) to graphane (H-100%). We find that the Young's modulus, tensile strength, and fracture strain of the functionalized graphene deteriorate drastically with increasing H-coverage up to about 30%. Beyond this limit the mechanical properties remain insensitive to H-coverage. While the Young's modulus of graphane is smaller than that of graphene by 30%, the tensile strength and fracture strain show a much larger drop of about 65%. We show that this drastic deterioration in mechanical strength arises both from the conversion of sp(2) to sp(3) bonding and due to easy-rotation of unsupported Sp(3) bonds. Our results suggest that the coverage-dependent deterioration of the mechanical properties must be taken into account when analyzing the performance characteristics of nanodevices fabricated from functionalized graphene sheets. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： 动力机械   电子控制  

ISBN: (数字)9787560949765 ISBN: (纸本)9787560949765

摘要： 本书阐述动力机械控制的演变，控制系统的基本组成、工作原理和品质评价，经典控制、现代控制、智能控制的基本概念和特点。主要内容以柴油机、汽油机、燃气轮机的动力性能、经济性能、排放性能为目标，以电子控制技术为重点，叙述各种动力机械控制系统的结构、控制参数的选择、控制模型的建立，综述理论和实验研究成果。整体控制、集中控制、综合优化是电控系统发展的重要趋势，书中与动力机械控制内容相衔接，介绍传统车辆、电动汽车、混合动力电动汽车、高性能船舶动力系统的特点，分析其性能，并以典型产品为实例，进行解析或仿真。

关键词： Poly(butylene succinate-co-terephthalate) (PBST) fibers   Tensile properties   Thermal properties   Isothermal crystallization  

摘要： Biodegradable copolymer poly(butylene succinate-co-terephthalate) (PBST), with 70 mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity of 2 km/min. The mechanical and thermal properties of the as-spun fibers were investigated through tensile test, DSC and TGA. Compared to poly(butylene terephthalate) (PBT) fibers, PBST fibers exhibited lower initial tensile modulus and higher tensile elongation at break which indicated their better flexibility. DSC results showed high melting temperature (ca.180.7 A degrees C) of PBST fibers helpful to the textile processing compared to other biodegradable polyesters. Furthermore, isothermal crystallization behaviors of PBST fibers at low and high supercoolings were investigated by DSC and DLI, respectively. The measurement of crystallization kinetics at low supercoolings indicated that Avrami exponent n for PBST fibers was at a range of 2.9 to 3.3, corresponding to the heterogeneous nucleation and a 3-dimensional spherulitic growth. Similar results were given for isothermal crystallization behavior at high supercoolings investigated by DLI technique. Additionally, the equilibrium melting temperature of PBST fibers was obtained for 206.5 A degrees C by Hoffman-Weeks method. Further investigation through DLI measurement provided the temperature at maximum crystallization rate for PBST fibers located at about 90 A degrees C, which was very useful to polymer processing.

关键词： tilting disk valve   major orifice region   minor orifice region   platelet activation   fluid dynamics   FSI   computer simulation  

摘要： The fluid dynamics during valve closure resulting in high shear flows and large residence times of particles has been implicated in platelet activation and thrombus formation in mechanical heart valves. Our previous studies with bileaflet valves have shown that large shear stresses induced in the gap between the leaflet edge and valve housing results in relatively high platelet activation levels, whereas flow between the leaflets results in shed vortices not conducive to platelet damage. In this study we compare the result of closing dynamics of a tilting disk valve with that of a bileaflet valve. The two-dimensional fluid-structure interaction analysis of a tilting disk valve closure mechanics is performed with a fixed grid Cartesian mesh flow solver with local mesh refinement, and a Lagrangian particle dynamic analysis for computation of potential for platelet activation. Throughout the simulation the flow remains in the laminar regime, and the flow through the gap width is marked by the development of a shear (ayes;which separates from the leaflet downstream of the valve. Zones of recirculation are observed in the gap between the leaflet edge and valve housing on the major orifice region of the tilting disk valve and are seen to be migrating toward the minor orifice region. Jet flow is observed at the minor orifice region and a vortex is formed, which sheds in the direction of fluid motion, as observed in experiments using PIV measurements. The activation parameter computed for the tilting disk valve at the time of closure was found to be 2.7 times greater than that of the bileaflet mechanical valve and was found to be in the vicinity of the minor orifice region, mainly due to the migration of vortical structures from the major to the minor orifice region during the leaflet rebound of the closing phase. [DOT: 10.1115/1.4000876]

关键词： 事故预防   农用设备   农业机械   接触安全装置   危险区   定义   危害   机械工程   职业安全   安全装置   安全工程   机械安全   安全要求   整地机具   规范   用户信息   工作场所安全  

标准号: BS EN ISO 4254-5-2009

摘要： This part of ISO 4254, intended to be used together with ISO 4254-1, specifies the safety requirements andtheir verification for the design and construction of mounted, semi-mounted and trailed power-drivensoil-working machines used in agriculture. In addition, it specifies the type of information on safe workingpractices (including residual risks) to be provided by the *** part of ISO 4254 deals with significant hazards (as listed in Annex A), hazardous situations and eventsrelevant to power-driven soil-working machines used as intended and under the conditions foreseen by themanufacturer (see Clause 4).This part of ISO 4254 is not applicable to:- spading machines;- machines fitted with a retractable device making them capable of working between two successive plantsin the same *** part of ISO 4254 is not applicable to environmental hazards or electromagnetic compatibility. It is notapplicable to hazards related to moving parts for power transmission, except for strength requirements forguards and barriers, nor to maintenance or repairs carried out by professional service *** 1 Specific requirements related to road traffic regulations are not taken into account in this part of ISO *** 2 Vibrations are not regarded as a significant hazard in the case of mounted, semi-mounted or trailed *** part of ISO 4254 is not applicable to power-driven soil-working machines which are manufactured beforethe date of its *** requirements of this part of ISO 4254 are different from those which are stated in ISO 4254-1, therequirements of this part of ISO 4254 take precedence over the requirements of ISO 4254-1.

关键词： Flagellin   Flagellar export   Force-denaturation   Protein mechanics   Multi-domain  

摘要： Bacterial flagellum is a nano-scale motility device constructed by self-assembly. During construction of the cell-exterior filament (the 'propeller'), subunit proteins (called flagellin) are thought to be exported through the hollow flagellum to the growing filament tip in an unfolded state. To gain insight into the unfolded state preceding any force-spectroscopy experiments on flagellin, we employed force-probe molecular dynamics simulations. Two schemes to attain an unfolded state suitable for efficient transport were examined: (i) stretching flagellin along its length;(ii) unzipping flagellin from its adjacently placed termini. Atomic-level unfolding pathways and the mechanical efforts involved under each scheme were obtained for the four-domain flagellin from S. typhimurium. Flagellin appeared stiffer and required larger unfolding forces when stretched as the relative sliding of beta-strands require the breaking of multiple hydrogen bonds at once. In contrast, unzipping requires lower unfolding forces as it mainly involves unraveling beta-sheets by breaking hydrogen bonds one by one. (C) 2009 Elsevier Inc. All rights reserved.

关键词： Nanostructured materials   Surface mechanical attrition treatment   Hot-working tool steel   Duplex chromizing treatment   Diffusion  

摘要： A nanostructured surface layer of about 20 mu m in thickness was fabricated on a hot-working tool steel (AISI H13) plate by means of surface mechanical attrition treatment (SMAT). Chromizing behaviors of the SMAT sample were investigated in comparison with its coarse-grained counterpart. Relative to the coarse-grained form, the Cr-diffusion depth was obviously enhanced by SMAT at various chromizing temperatures, with a maximum increment at 600 degrees C. A duplex chromizing treatment at 600 degrees C followed by at a higher temperature led to the formation of a much thicker chromized surface layer (up to 30 mu m in thickness) on the SMAT sample. This might be attributed to the formation of a large amount of nanosized chromium compounds in the surface layer at 600 degrees C, which retarded growth of nano-sized ferrite grains and improved the Cr diffusion at higher temperatures. Gradient distributions of Cr concentration, microstructure and hardness were formed in the chromized surface layer in the SMAT steel after the duplex chromizing treatment, leading to an obvious enhancement in the wear resistance. (C) 2009 Elsevier B.V. All rights reserved.