关键词： high-entropy alloys   amorphous-monocrystalline composite   nanowires   size effects   molecular dynamics simulation  

摘要： The atomic models of amorphous and monocrystalline composite AlFeNiCrCu high-entropy alloy nanowires were established via the molecular dynamics method. The effects of amorphous structure thickness on mechanical properties and deformation mechanism were investigated by applying tensile and compressive loads to the nanowires. As the thickness of amorphous structures increases, the tensile yield strength decreases, and the asymmetry between tension and compression decreases. The tensile deformation mechanism transforms from the coupling interactions between stacking faults in crystal structures and uniform deformation of amorphous structures to the individual actions of uniform deformation of amorphous structures. During the tensile process, the nanowires necking appears at amorphous structures, and the thinner amorphous structures, the more prone to necking. The compressive deformation mechanism is the synergistic effects of twins and SFs in crystal structures and uniform deformation of amorphous structures, which is irrelevant to amorphous structure thickness. Remarkably, amorphous structures transform into crystal structures in the amorphous and monocrystalline composite nanowires during the compressive process.

关键词： Cyclic loading   coal   nanoindentation   molecular dynamics simulation   dissipated energy  

摘要： By studying the key mechanical properties and their damage mechanisms of coal at the nanoscale, a better understanding of the strength and damage of coal in complex stress environments can be obtained. The micro-mechanical properties and damage mechanism of coal under cyclic loading were investigated by nanoindentation experiment and molecular dynamics (MD) simulation of nanoindentation. Molecular dynamics simulations were conducted by building models containing approximately 2.5 million atoms, it was found that the coal substrate showed cyclic hardening under cyclic loading. The hardness and elastic modulus of the coal samples measured by the nanoindentation experiment gradually increased from 0.476 GPa to 0.740 GPa and from 4.70 GPa to 5.997 GPa, respectively. The simulation results display a good agreement with the experimental results. The simulation results show that the plastic damage of coal substrate under cyclic loading is related to the stretching, bending, rotation, and fracture of chemical bonds. At the same time, the formation and recovery of elastic deformation are related to the changes of van der Waals force, Coulomb force, and bond angle. Additionally, the carbon hexatomic ring in the coal macromolecule is critical in resisting the influence of loading.

关键词： molecular dynamics   microstructure   mechanical properties   magnetorheological fluid   sedimentation stability  

摘要： Magnetorheological (MR) fluids are smart materials that show enormous potential in vibration control, mechanical engineering, etc. However, the effects of the solid-liquid interface strength and the interaction strength between carrier liquid molecules on the mechanical properties and sedimentation stability of MR fluids have always been unresolved issues. This work presents a new type of MR fluid that has a novel carrier liquid, i.e., silicone oil (SO) mixed with a hydroxyl-functionalized ionic liquid (IL-OH). An all-atomic Fe/SO/IL-OH interface model for studying the relationship between mechanical properties and interface strength and intermolecular interactions is established. On the basis of simulation results and theoretical analyses, the mechanical properties and sedimentation stability of the SO/IL-OH-based MR fluids are thoroughly investigated by experiments. The results show that functional ionic liquids significantly improve the mechanical properties and sedimentation stability of MR fluids. These results are essentially attributed to the stronger solid-liquid interface strength, van der Waals forces, and hydrogen bonds between the silicone oil and the functional ionic liquid. The explicit results not only help elucidate the numerous phenomena involved in the research process for MR fluids at the atomic scale but also provide insightful information on the fabrication of high-performance MR fluids.

关键词： 气化细渣   残碳   机械活化   活化能   陶粒  

摘要： 随着我国煤气化技术的快速发展,气化渣的产生和排放量逐年增加。煤气化细渣的大量堆存,给当地的环境保护造成了巨大的压力,已经成为限制煤化工产业基地可持续发展急需解决的重大问题。本文针对气化细渣中残碳反应活性低和转化难度大的问题,研究了机械活化法对气化渣残碳反应动力学的影响。采用Coats-Redfern法分析了机械活化对残碳反应活化能的作用规律。结果表明,机械活化8 h,残碳燃烧反应活性显著提高,650℃下的活化能由63.2 kJ·mol^(−1)降到28.4 kJ·mol^(−1)。不添加其他化学试剂,1000℃烧制高强度轻质陶粒,其堆积密度为0.867 g·cm^(−3),筒压强度为7.67 MPa。相关研究可以为我国气化细渣的资源化利用提供一定的数据和技术基础。

关键词： 工程机械动力   新能源   碳达峰  

摘要： 非道路移动机械排放标准的不断升级,迫使工程机械必须加装复杂的后处理装置,动力系统的成本急剧上升。同时,经过10多年的发展,汽车电动化的发展为工程机械电动化打下了零部件基础,电驱动系统成本不断下降。在碳达峰、碳中和的大背景下,新能源的开发应用势头强劲,工程机械行业为顺应趋势,也将会加速电动化的进程。从政策、市场、技术等方面分析介绍工程机械电动化的现状及发展趋势。

关键词： 电控机械式自动变速器   AMT   动力学分析   NE:DC   MATLAB  

摘要： 电控机械式自动变速器(Automated Mechanical Transmission, 简称AMT)在我国具有良好的市场前景,其结构简单、生成继承性好。建立汽车动力性、等速油耗和NEDC循环工况油耗的数学模型,分析AMT的起步换挡过程及相应的离合器数学模型,通过MATLAB/Simulink和Stateflow,对AMT进行动力性和经济性的仿真分析,并在NEDC循环工况下采用车速差和车速差变化率的双参数发动机节气门开度模糊控制,同时制定该循环工况的经济性换挡规律。结果表明:起步时间由最低挡传动比大小决定,传动比越大,起步时间越短,八挡AMT起步时间最短,仅为1.48s,相较于最长起步时间1.61s的六挡AMT缩短了8.1%;加速时间不仅与起步时间有关,还在很大程度与挡位数量、各挡传动比大小和换挡规律息息相关,六挡AMT的百公里加速时间最短,为13.16s,相较于最长时间14.18s的五挡AMT缩短了7.2%;相同情况下,增加挡位数量会改善汽车的燃油经济性,十挡AMT的NEDC循环工况百公里油耗最低,为6.533L·(100km)^(-1),相较于最高百公里油耗6.793L·(100km)^(-1)的五挡AMT缩短了3.8%。

关键词： 机械通气   氢吗啡酮   咪达唑仑   镇静镇痛   血流动力学  

摘要： 研究氢吗啡酮联合咪达唑仑应用对机械通气患者镇痛镇静效果及血流动力学的影响。方法:选择68例机械通气患者,通过对照研究,分析镇静效果结果:观察组的镇静效果更优(P<0.05)。结论:机械通气患者通过氢吗啡酮联合咪达唑仑进行镇痛镇静,麻醉效果优良。机械通气患者所受到的伤害刺激具有多源性,除本身的疾病因素外,ICU环境因素,气管插管,频繁的吸痰、穿刺等医疗护理操作均可能对患者产生强烈的心理和生理刺激,而合理的使用镇静或镇痛药可消除心理和生理两方面的不良反应。

关键词： 纳米多晶铁   模拟XRD谱   晶粒尺寸   沿晶裂纹   氦效应  

摘要： 采用分子动力学方法研究了晶粒尺寸对掺氦纳米多晶铁机械性能的影响。在拉伸形变过程中,纳米多晶铁将产生裂纹与晶格畸变,通过模拟XRD谱探索二者之间的联系。拉伸模拟结果显示,由于晶界氦原子的引入,峰值应力将显著减小。另外,在拉伸模拟中观察到,沿晶裂纹的产生与长大随着晶界氦原子的引入而增强。研究结果表明,晶界氦原子能够促进沿晶裂纹的产生,而裂纹的大小和数量随着晶粒尺寸的增加而增加。在拉伸过程中,纳米多晶铁的XRD谱显示,{200}峰与{211}峰发生了明显的分裂。在应变范围6%~10%之间,与掺氦前相比,掺氦后纳米多晶铁的XRD谱中副峰的衍射角较高。随着晶粒尺寸的增加,副峰峰位逐渐向高衍射角移动,且裂纹萌生逐渐增强。这说明XRD谱显示的晶格畸变与沿晶裂纹所致的机械性能退化密切相关。

关键词： 上肢康复机器人   机械结构   ADMAS   动力学分析  

摘要： 社会的各个领域已经将如何把机器人技术应用完善作为行业的新思考点,发展机器人技术需要多学科多领域的交叉研究,在工业机器人发展较为成熟的情况下,机器人开始用于医疗方面。进行了上肢康复机器人机械结构设计,其主要由执行机构、驱动机构和控制系统上肢康复机器人这三大部分组成。所设计的上肢康复机器人定位机械臂的设计需要完成器械的抓取、移动以及定位。本该设计结构采用关节式设计,关节型的优点是传动时操作较为精确,零件与零件之间的结构简单,需要用到的空间也较小,使其符合医疗器械的设计要求。本设计主要对机构的执行机构和驱动机构作详细的介绍。完成了上肢康复机器人的ADMAS动力学分析仿真研究,基于Adams的各构件的运动轨迹曲线一致,验证了所做上肢康复机器人运动学分析的正确性,以期为康复医学工作作出相应的贡献。

关键词： Seals   hydrodynamic lubrication   cavitation   surface topography   numerical simulation  

摘要： A two-scale homogenization method for modelling the hydrodynamic lubrication of mechanical seals with isotropic roughness was developed and presented the influence of surface topography coupled into the lubricating domain. A linearization approach was derived to link the effects of surface topography across disparate scales. Solutions were calculated in a polar coordinate system derived based on the Elrod cavitation algorithm and were determined using homogenization of periodic simulations describing the lubrication of a series of surface topographical features. Solutions obtained for the hydrodynamic lubrication regime showed that the two-scale homogenization approach agreed well with lubrication theory in the case without topography. Varying topography amplitude demonstrated that the presence of surface topography improved tribological performance for a mechanical seal in terms of increasing load-carrying capacity and reducing friction coefficient in the radial direction. A Stribeck curve analysis was conducted, which indicated that including surface topography led to an increase in load-carrying capacity and a reduction in friction. A study of macro-scale surface waviness showed that the micro-scale variations observed were smaller in magnitude but cannot be obtained without the two-scale method and cause significant changes in the tribological performance.