关键词： 双动力   大型养路机械   电传动   液力传动  

摘要： 针对现有铁路大型养路机械驱动方式的局限性,提出将双动力源应用于铁路大型养路机械的思路,分析了电力/内燃双动力在铁路大型养路机械上的应用优势和应用范围,并对技术难点进行了阐述,最后简单介绍了电力/内燃双动力在48磨头钢轨打磨车的应用。

关键词： 旋翼无人机   飞行机械臂   动力学建模   预测控制   飞行仿真  

摘要： 旋翼飞行机械臂(rotorcraft aerial manipulator,RAM)系统是安装在飞行机器人上的可操作型机械臂,悬停模式下执行准确的空中操作时旋翼无人机与所加机械臂之间存在相对扰动,通过分离机械臂与飞行机器人进行动力学建模并不能有效消除这种扰动.本文基于对相互扰动力学作用的分析建立整体动力学模型,并在悬停飞行模式下将其简化为线性控制参考模型.进而对旋翼系统控制延时所引起的动力学扰动进行补偿,同时设计预测控制器来消除末端执行器的位置和姿态误差.最后,在存在内部和外部扰动的情况下,设定销钉插入操作任务进行控制方法的对比仿真.末端执行器位姿偏差的仿真结果表明了模型结构与控制方法的有效性.

关键词： 机电工程   旋量理论   柔性机械臂   刚柔耦合   动力学模型  

摘要： 针对作大范围空间运动的机械臂,提出了基于变形旋量理论的工业机器人机械臂刚柔耦合动力学建模方法;研究了机械臂空间变形耦合和扭转变形对动力学特性的影响;建立了作大范围空间运动柔性机械臂的刚-柔耦合动力学理论模型,该模型将机械臂应用到空间范围,并考虑扭转变形的影响。对模型做计算仿真分析,将分析结果与传统零次模型进行比较。结果表明:作大范围运动机械臂动力学方程的建立,旋量理论的应用解决了传统数学方法只限于平面运动的局限性;大范围运动与机械臂变形之间的耦合,对于机械臂杆件和终端有一定的影响;计及变形耦合影响的机械臂动力学特性将发生变化,机械臂振动频率会提高。

关键词： ADAMS   Pro/E   金属成形加工机械执行机构   仿真   柔性  

摘要： 目的应用图解法对金属成形加工机械执行机构进行设计,并基于ADAMS和Pro/E软件对机构进行建模仿真及分析。方法根据测量出各铰链受力情况选取典型构件作为柔性构件,在ADAMS柔性模块中对相应刚性构件进行柔性替换,并比较冲头的位移、速度、加速度、曲柄力矩等曲线。结果当机构高速运转时,原动件速度为360(°)/s,柔性构件对冲头的位移、速度、加速度都造成了影响,其中对位移曲线影响不大,对速度、加速度曲线影响明显,对机构的稳定性造成了一定影响。结论当设计高速机构时,必须考虑构件的柔性因素对机构运动特性的影响。

关键词： GRAIN size   STRAINS & stresses (Mechanics)   POLYCRYSTALS   GRAPHENE   MOLECULAR dynamics -- Simulation methods   DEFORMATIONS (Mechanics)   FRACTURE strength  

摘要： We investigate the mechanical properties of polycrystalline graphene deforming under uniaxial tension by using molecular dynamics simulations, focusing on the effects of grain size, temperature and strain rate. It is found that polycrystalline graphene with smaller grain size shows a larger drop of Young's modulus and fracture strength. For the polycrystalline graphene with grain size of 7.5 nm, the Young's modulus and fracture strength is about 80% and 40% that of single-crystalline graphene, respectively. Our simulation results also reveal that the Young's modulus and fracture strength of polycrystalline graphene are more sensitive to the changes of temperature and strain rate than that of single-crystalline graphene. When temperature increases from 100 to 1200 K, the fracture strength of polycrystalline graphene reduces by around 45%. At room temperature (300 K), the fracture strength of polycrystalline graphene increases by 10% as the strain rate increases from 5 x 10(-5) to 5 x 10(-3) ps(-1). Furthermore, the strain rate has a stronger influence on the fracture strength of polycrystalline graphene at a higher temperature than at a lower temperature;while the temperature has a stronger influence at a lower strain rate than at a higher strain rate. Our study thus provides a comprehensive understanding of the mechanical properties of polycrystalline graphene. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Incubation time   Diffusion model   Activation energy   Growth kinetics   Adherence   Tribology  

摘要： In the present study, the growth kinetics and mechanical properties of Fe2B layers formed on the AISI D2 steel are investigated. A mathematical model for studying the growth kinetics of Fe2B layers on the AISI D2 steel is proposed for the powder-pack boriding. This process is carried out in the temperature range of 1123-1273 K for treatment time ranging from 2 to 8 h. This kinetic model is based on solving the mass. balance equation at the (Fe2B/ substrate) interface to evaluate the boron diffusion coefficients through the Fe2B layers in the temperature range of 1123-1273 K. The formed boride layers are characterized by different experimental techniques such as light optical microscopy, scanning electron microscopy, XRD analysis and the Daimler-Benz Rockwell-C indentation technique. A tribological characterization is also performed using a Flint TE77 tribometer under dry sliding conditions. The boron activation energy for the AISI D2 steel is estimated as 201.5 kJ mol(-1) based on our experimental results: This kinetic model is also validated by comparing the experimental Fe2B layer thickness with the predicted value at 1243 K for 5 h of treatment. A contour diagram relating the layer boride thickness to the bonding parameters is suggested to be used in practical applications.

关键词： drug release rate   hydrophilic matrix systems   mechanical stress and dissolution   modified release drug product   texture analysis  

摘要： The objective of this study was to determine the influence of mechanical stresses simulating gastrointestinal contraction forces of 2.0 N (stomach) and 1.2 N (intestine) on the gel properties and drug release characteristics from sustained release swelling and eroding hydrophilic matrices during dissolution studies. Two batches of tetracycline-sustained release tablets containing hydroxypropyl methyl cellulose (HPMC) were manufactured and subjected to USP apparatus II (pH 2.2 buffer) dissolution studies. Hydrated tablets were periodically removed, placed in a petri dish, and multiple times (six cycle) compressed with a flat-ended probe (diameter 1.3 cm) on a texture analyzer at preprogrammed force of either 2.0 or 1.2 N to determine force-distance profiles and changes in drug release rate. The calculated similarity factor values showed dissimilar dissolution profiles using standard dissolution profile as a reference. The similarity factor (f (2)) values were especially lower than 50 at 2.0 N and, when profiles between the two batches compressed at 1.2 and 2.0 N, were compared with each other. The changes in dissolution pattern and release rate were significantly different after 4 h of dissolution. At 8 h, tablets were fully hydrated and no force could be detected by the probe, indicating a very soft gel matrix. It appears that the contraction forces in the stomach and intestine are capable of altering drug release from modified release hydrophilic matrices during transit in the human GI tract. Accounting for these forces during dissolution can enhance predictions of in vivo drug release, achieve better in vitro and in vivo correlation, introduce improvement in dissolution methods, and better understand the critical quality attributes (CQAs) and factors in quality by design (QbD) during the product development process.

关键词： Mechanical alloying   Crystallization kinetics   Spark plasma sintering   Mechanical properties  

摘要： Amorphous Ni53Nb20Ti10Zr8Co6Ta3 powders were successfully fabricated by mechanical alloying. The glass-forming ability and crystallization behavior of the synthesized alloy powders were investigated by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The non-isothermal crystallization kinetics were analyzed by the Johnson-Mehl-Avrami equation. The crystallization of the amorphous Ni53Nb20Ti10Zr8Co6Ta3 powders exhibits two distinct steps, and the values of the Avrami exponent n implies that the crystallization of the first and second steps are dominated by interface-controlled three-dimensional growth as well as the volume-diffusion-controlled two-dimensional growth, respectively. In addition, the bulk crystallized alloys consolidated from the amorphous powders by spark plasma sintering exhibit high fracture strength of 3169 MPa and ultra-high hardness of 1069 HV. The compressive fracture strength and fracture strain of the as sintered alloy at 1073 K reach 2020 MPa and 7.6%, respectively. (C) 2015 Elsevier Ltd. All rights reserved.

关键词： Non-linear dynamics   Reduced order systems   Slow invariant manifold  

摘要： The dynamics of a non-linear electro-magneto-mechanical coupled system is addressed. The non-linear behavior arises from the involved coupling quadratic non-linearities and it is explored by relying on both analytical and numerical tools. When the linear frequency of the circuit is larger than that of the mechanical oscillator, the dynamics exhibits slow and fast time scales. Therefore the mechanical oscillator forced (actuated) via harmonic voltage excitation of the electric circuit is analyzed;when the forcing frequency is close to that of the mechanical oscillator, the long term damped dynamics evolves in a purely slow timescale with no interaction with the fast time scale. We show this by assuming the existence of a slow invariant manifold (SIM), computing it analytically, and verifying its existence via numerical experiments on both full- and reduced-order systems. In specific regions of the space of forcing parameters, the SIM is a complicated geometric object as it undergoes folding giving rise to hysteresis mechanisms which create a pronounced non-linear resonance phenomenon. Eventually, the roles played by the electro-magnetic and mechanical components in the resulting complex response, encompassing bifurcations as well as possible transitions from regular to chaotic motion, are highlighted by means of Poincare sections. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Titanium alloys  

摘要： To improve alloy properties and the distribution level of TiB2 particles in the alloy matrix, mechanical alloying was used to prepare the Cu-TiB2 alloy. But even after long-time ball milling, the in situ reaction between Cu-B and Cu-Ti alloy powders still cannot be observed in the whole process. The kinetics of the in situ reaction during high-temperature heat treatment was first investigated and led to the following results. With the increase of heat-treatment time t or diffusion depth X, both the moving speed Delta x/Delta t of reaction front edge and nucleation rate Z(x) of TiB2 particles decrease at a fast rate and finally stabilize at a very low level. The falling rate of moving speed Delta x/Delta t increases with the decrease of temperature. Although the C-Ti' value of the Ti element gives a poor effect on the moving speed Delta x/Delta t, it significantly affects the nucleation rate of TiB2 particles, and its falling rate increases with a decreasing C-Ti' value. And for the same diffusion depth X and C-Ti', the nucleation rate of TiB2 decreases with increasing the heat-treatment temperature. These results were verified by the microstructure change after the heat treatments at temperatures of 773 K, 973 K, and 1173 K (500 degrees C, 700 degrees C, and 900 degrees C), respectively. Finally, the best combination of ball-milling and heat-treatment conditions was obtained. (C) The Minerals, Metals & Materials Society and ASM International 2015