关键词： 动力机械泵   安装   运行   操作故障   分析与处理  

摘要： 介绍了动力机械泵的工作原理和结构,安装、运行操作的注意事项及故障诊断、处理方法,以便于动力机械泵的维护和管理。

关键词： 静压机械密封   动力学   微小扰动   刚度   阻尼  

摘要： 机械密封动力学性能对密封系统稳定性有很大的影响,微小的振动会导致密封泄漏量增加和端面磨损加剧。根据机械动力学基本原理,建立了流体静压机械密封轴向、角向振动的动力学耦合方程,并通过简化将其转化成相互独立的单自由度二阶微分方程。结合辅助密封圈的动态参数求解方法,通过MATLAB编程求出系统在内部微小扰动作用下,密封环在轴向和角向的动态响应曲线。分析表明,综合考虑振荡频率和振动幅度等因素,端面锥角保持在大于或等于2’的附近范围内,转折半径保持在大于或等于130mm的附近范围内,密封系统能够保持较好的稳定性。

关键词： 康复机械训练手   结构设计   虚拟样机   动力学分析  

摘要： 医用康复机械训练手是一种辅助人体手部关节运动的机械系统,它根据人体手部结构特点以及可穿戴康复机械训练手的功能要求,在原有康复机械手机械结构的设计基础上,利用三维设计软件对已有康复机械手的结构进行改进设计,使外骨骼康复机械手能够满足辅助人体手部康复的功能。并利用多体动力学软件ADAMS建立康复机械训练手虚拟样机模型,分别从空手和抓握杯子两种情况对机械训练手进行动力学分析,分析结果得到两气缸驱动的合理范围和结构尺寸,为机械手的设计、优化与运动控制提供参考数据。

关键词： Geopolymer   Metakaolin   Nanoindentation   Nanomechanical properties   Reaction kinetics  

摘要： A multiscale study is presented of the reaction kinetics, phase formation, mechanical properties of metakaolin-based geopolymers by varying Si/Al ratios of 1.2-2.2 and Na/Al ratios of 0.6-1.2. Macro- and nano-mechanical properties of geopolymer samples were determined by unconfined compression testing and grid nanoindentation technique, respectively. The latter, in combination with statistical deconvolution, also enables the extraction of generally 4 distinct phases together with their nano mechanical properties and volumetric fraction within the synthesized geopolymers. Moreover, the reaction kinetics, phase formation (particularly geopolymer gel development), and mechanical property development were investigated by characterizing geopolymers cured at the final setting time, 7, and 28 days. Phase formation was characterized by Fourier transform infrared spectroscopy (FTIR) via monitoring the evolution of the Si-O-T (T: Si or Al) and Al-O bonds. Results illustrate that the fraction of geopolymer gels dominantly governs the mechanical behavior, both of which increase with the Si/Al and Na/Al molar ratios, while the final setting time increases with the Si/Al ratio, but decreases with the Na/Al ratio. The chemical composition for the best mechanical performance of the studied geopolymers is a Si/Al ratio of 1.7 and Na/Al ratio of 0.9. The relationships among geopolymer chemical compositions, geopolymer gel formation rate, and macromechanical properties are also discussed. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Coral skeletons   Reef sediments   Reef diagenesis   Dissolution kinetics  

摘要： Ocean acidification is widely accepted as a primary threat to coral reef populations. Negative physiological effects include decreased calcification rates, heightened metabolic energy expenditure, and increased dissolution of coral skeletons. However, studies on the dissolution of coral skeletons structures under ocean acidification conditions and their implications on sediments remain scarce. In this work, we examined skeletal dissolution kinetics from four of the most representative hermatypic corals of the Eastern Pacific coasts (Pocillopora, Porites, Pavona, and Psammocora). Samples were treated with a highly acidic solution for defined periods of time, and measurements of dissolved calcium ([Ca+2]) were used to evaluate the kinetics of coral skeleton dissolution. All genera tests except Porites showed a zero reaction rate. Porites exhibited a first-order reaction and a faster reaction rate than other genera. Compression strength tests and skeletal density did not correlate with reaction rate. Pavona showed greater structural strength. Porites were the most susceptible to acidic dissolution compared to other genera tested due to their morphology, i.e., possession of the largest surface area, suggesting a high vulnerability under low-pH conditions. The hierarchical response in dissolution kinetics among coral genera tested suggests that the most soluble coral might act as a buffer under ocean acidification conditions.

关键词： Plasma paste boriding   Commercially pure titanium   Growth kinetics of borides   Boron activation energy   Hardness   Wear resistance  

摘要： In this study, the plasma paste boriding (PPB) was applied in order to produce the boride layers on commercially pure titanium (Cp-Ti). PPB process was carried out in 50% H2-50% Ar atmosphere under a reduced pressure at various parameters (temperature and duration). The boride layers consisted of two zones: a continuous TiB2 zone close to the surface and a zone with TiB whiskers below the first one. The growth of both zones obeyed the parabolic, growth law. The model of growth kinetics of such layers was analyzed. The parabolic growth constants were calculated and the boron diffusion coefficients were determined. Activation energy values of 123.33 and 178.71 kJ mol(-1) were obtained for TiB2 and TiB phases, respectively. The calculated value for TiB2 phase was lower compared to the other boriding processes. Microhardness profile was determined for the layer of the highest depth. The maximal microhardness was characteristic of TiB2 zone (2452 HV). Nanomechanical properties (nanohardness and Young's modulus) were studied using the nanoindenter. TiB2 zone was characterized by the nanohardness of 2867.6 HV and indentation modulus E-IT= 383 GPa. Wear resistance of plasma paste borided layers was up to 9 times higher when comparing to the untreated Cp-Ti. (C) 2017 Elsevier B.V. All rights reserved.

摘要： While most existing theoretical studies on the borophene are based on first-principles calculations, the present work presents molecular dynamics simulations for the lattice dynamical and mechanical properties in borophene. The obtained mechanical quantities are in good agreement with previous first-principles calculations. The key ingredients for these molecular dynamics simulations are the two efficient empirical potentials developed in the present work for the interaction of borophene with low-energy triangular structure. The first one is the valence force field model, which is developed with the assistance of the phonon dispersion of borophene. The valence force field model is a linear potential, so it is rather efficient for the calculation of linear quantities in borophene. The second one is the Stillinger-Weber potential, whose parameters are derived based on the valence force field model. The Stillinger-Weber potential is applicable in molecular dynamics simulations of nonlinear physical or mechanical quantities in borophene.

关键词： 机器人   动力学   机械臂  

摘要： 机械臂的动力学原理主要有牛顿-欧拉方程和拉格朗日平衡法。动力学设计是指导机械臂设计的核心,本文根据机械臂的运用领域不同,从按摩用机械臂,果蔬采摘用机械臂和其他用机械臂三个方面分别举例说明机械臂的动力学设计,为机器人的进一步应用提供参考。

关键词： confinement   electrospinning   size-dependent   supramolecular   nanofiber  

摘要： The microstructure of polymer matrix under cylindrical confinement is key to understanding the size-dependent thermomechanical behavior of electrospun nanofibers. Coarse-grained molecular dynamics simulation was applied here to probe polymer systems under cylindrical confinement, prepared with or without pre-stretching. Simulation results showed that below a certain radius, a noticeable increase of the elastic modulus is observed with the decrease of the radius of cylindrical confinement. This size-dependent mechanical behavior correlated to the degree of polymer chain orientation. Modulation of density and bond orientation in the radial direction was observed: the density and bond orientation began to oscillate, increasing the oscillation amplitudes with decreases in the radius. Such behavior suggests that the cylindrical confinement enhances the bond alignment of the entire fiber and not in the near-surface layers only. The unstretched fibers had uniform density distribution along the fiber axis, while the stretched fibers demonstrated a fluctuation in density distribution. The crossover radius of size-dependent behavior was two orders of magnitude smaller than observed in real experiments, demonstrating that the confinement affects some internal fiber scale, which exceeds the scale of individual macromolecules, and this internal scale may be related to supramolecular structures of the polymer matrix rather than the individual macromolecules. (C) 2017 Wiley Periodicals, Inc.