关键词： 纯电动汽车   机械式变速器   动力换挡   整车性能  

摘要： 针对纯电动汽车驱动特点,研究了一种新型的面向纯电动汽车的动力换挡式机械变速器,该变速器由单作动件实现换挡,传动结构与机械式变速器相似。推导并建立了换挡过程的数学模型,研究了变速器转矩相与惯性相动态性能,结合台架实验结果,论证了研发的变速器在高低挡切换时,动力交替过程保持连续变化,能够满足快速平稳动力换挡性能。对变速器在整车应用方面进行了研究,结果表明,与其他变速器相比,研发的变速器能够较好地兼顾电动汽车整车性能和成本要求。

关键词： 船舶   动力机械   螺旋桨   维修养护  

摘要： 船舶是水上运输的主要工具,在其动力机械中,螺旋桨是较为重要的一部分,一旦螺旋桨出现问题,便会对船舶航行造成影响。为此,应当做好螺旋桨的检修和养护。基于此点,文章首先简要分析了船舶螺旋桨的构成,并在此基础上对船舶动力机械中螺旋桨的检修内容及养护方式。期望通过本文的研究能够对延长船舶螺旋桨的使用寿命及确保船舶航行的安全性有所帮助。

关键词： 遥控维护   主从机械手   动力学   有限元  

摘要： 主从机械手是实现遥控维护的关键设备,研制适合的遥控维护的主从机械手是遥控维护系统建设的重要内容。为了优化主从机械手的结构设计,对遥控维护主从机械手进行了动力学分析。通过建立主从机械手的整机有限元模型,进行整机静力学预分析;通过模态分析,计算出主从机械手的前6阶的固有频率以及相应的振型,分析得出主从机械手的薄弱零部件,为结构的优化设计提供了有益的结论。

关键词： 多柔体   机械臂   铰间隙   动力学   固有频率  

摘要： 地面长臂机械研究中一般都将铰当成理想铰处理而忽略铰间隙的影响,为得到更符合实际运动学规律和动力学特性的结果,首先,采用Lankarani-Nikravesh模型并选取合适的摩擦因数,分析加入第1节臂和加入全部4节臂油缸连接旋转铰间隙接触摩擦的影响;其次,建立对应的多柔体臂架的刚柔混合模型,对理想铰和铰间隙臂架模型的末端轨迹和振动特性进行数值分析。结果表明:加入铰间隙模型的末端振动位移比理想铰模型的末端位移增大,第1节臂液压油缸最大受力值也对应增大;考虑铰弹性的第1阶固有频率比理想铰模型有所降低,证明此类机械铰间隙的影响不能忽略。最后,通过臂架实验台验证了模型的合理性和数值仿真的正确性,为此类机械设计和工程应用提供参考。

关键词： Perfect and imperfect Timoshenko microbeams   Thermo-mechanics   Bifurcation diagrams   Modified couple stress theory   Temperature-dependent mechanical properties  

摘要： This paper investigates the three-dimensional motion characteristics of perfect and imperfect Timoshenko microbeams under mechanical and thermal forces;the mechanical properties of the microbeam are considered temperature-dependent. The centerline of the microbeam is considered to be extensible and the equations of motion for the longitudinal, transverse, and rotational motions are derived by means of the extended Hamilton's principle and the modified couple stress theory. These three coupled nonlinear partial differential equations are discretized by means of Galerkin's technique, yielding a set of second-order nonlinear ordinary differential equations. These equations are solved by means of the pseudo-arclength continuation technique and via an eigenvalue analysis, for the nonlinear and linear analyses, respectively. The geometrically perfect microbeam remains stable at its original static equilibrium position up to the temperature when it loses stability by divergence via a supercritical pitchfork bifurcation;the post-buckling state is obtained and resonant response over it is analysed. For the initially imperfect microbeam, as the temperature is increased, the initial curvature amplitude increases and no instabilities occur;the resonant response of the system over the new deflected configuration is examined numerically. The effect of different parameters on the nonlinear behaviour of the system is studied. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Bi2Te3   Van der Waals bonding   compression properties   molecular dynamics  

摘要： Along the c axis of the crystal lattice, Bi2Te3 has periodic quintuple layers " Te1 Bi Te2 Bi Te1-" which are connected by Van der Waals bonding. The weak bonding between Te1-Te1 layers substantially affects the mechanical properties of Bi2Te3. In the work discussed in this paper, the molecular dynamics method was used to study the mechanical properties of cuboid single-crystal of bulk Bi2Te3 under compressive loads. The emphasis was on the effects of the Van der Waals bonding on the deformation and failure mechanism. The molecular dynamics simulation results revealed that Van der Waals bonding has a dominant effect on the mechanism of deformation, and fundamentally determines the ultimate stress and fracture strain. Furthermore, the compressive load along the a and c axes lead to quite different failure behavior, which can be distinguished by their specific effects on the deformation of the Van der Waals bonding. However, only models with the load along the a axis dramatically demonstrate the effect of strain rate on the stress-strain curves, in accordance with the poor structural stability.

关键词： Flax   Surface treatments   Permeability   Consolidation  

摘要： Chemical treatments are widely employed to improve the fiber-matrix adhesion in composites based on eco-friendly fibers such as flax. To better understand the influence of these treatments on processing behavior, this study characterized the surface chemistry and morphology of woven flax fabrics treated by acetone, alkaline, silane and diluted epoxy. Flax/epoxy composites were then manufactured by resin infusion and the flow front and preform thickness evolution was monitored. The alkaline treatment was shown to result in a 50 % increase in equivalent permeability due to an increase in porosity which led to a decrease in flexural properties. The processing results were found to be in good agreement with predictions of a 1-dimensional model. This study suggests that infusion times are not considerably affected by the observed changes in surface energy. However, other implications of the treatments such as an increase in fibrillation can alter the infusion times significantly.

关键词： Mechanical properties   nanopores   CoSb3   molecular dynamics  

摘要： Recently, many experimental studies have reported that inserting nanopores into thermoelectric materials can both remarkably reduce the thermal conductivity and significantly improve the thermoelectric performance of the target material. Research on nanoporous materials has thus been attracting much attention worldwide. However, most of the studies mainly focus on the preparation of nanoporous material and the effect of different geometrical sizes of nanopores on thermal conductivity and thermoelectric properties of the nanoporous material. In this paper, the mechanical behavior of crystalline CoSb3 with nanopores under uniaxial tensile/compression is studied by means of the molecular dynamics method. The emphasis is on the influence of porosity, temperature and strain rate on the tensile/compressive mechanical behavior of nanoporous CoSb3. The simulation results show that both failure patterns under tension/compression are typical brittle fractures. The elastic modulus decreases with the growing porosity, and the porosity and the elastic modulus are inversely proportional to each other. The increase of temperature results in a linear degradation of the elastic modulus and the ultimate strength. The elastic modulus and the ultimate strength under uniaxial compression are greater than those under uniaxial tension. The present study sheds light on the future application of nanoporous CoSb3 thermoelectric materials.

关键词： Micropillars   Mechanotransducion   Correlation   Nuclear dynamics   Focal adhesion  

摘要： Cells sense physical cues at the level of focal adhesions and transduce them to the nucleus by biochemical and mechanical pathways. While the molecular intermediates in the mechanical links have been well studied, their dynamic coupling is poorly understood. In this study, fibroblast cells were adhered to micropillar arrays to probe correlations in the physical coupling between focal adhesions and nucleus. For this, we used novel imaging setup to simultaneously visualize micropillar deflections and EGFP labeled chromatin structure at high spatial and temporal resolution. We observed that micropillar deflections, depending on their relative positions, were positively or negatively correlated to nuclear and heterochromatin movements. Our results measuring the time scales between micropillar deflections and nucleus centroid displacement are suggestive of a strong elastic coupling that mediates differential force transmission to the nucleus. (C) 2015 Elsevier Inc. All rights reserved.