关键词： 空间机械臂   动力学建模   捕获目标   接触碰撞  

摘要： 空间机械臂的载体处于自由漂浮状态,载体与机械臂之间存在运动学与动力学耦合行为,导致其运动学、动力学分析与控制比地面机械臂复杂得多,而建立精确的动力学模型和高效的控制策略是空间机械臂研究的重点与难点。对空间机械臂动力学建模方法及精细动力学建模进行了详细综述;总结了姿态调整运动规划、非完整路径规划及避奇异位形路径规划等运动规划方法;概述了空间机械臂捕获目标过程的碰撞动力学建模和控制策略研究。在此基础上指出了当前空间机械臂在动力学建模与控制方面存在的问题与不足,并对有待于进一步研究的若干问题进行了展望。

关键词： 中国机械工业企业管理协会   中国机械500强   发布会   中国企业   新闻界   领导   朋友  

摘要： 尊敬的各位领导、各位来宾、新闻界的朋友们： 今天，我们在这里举行2016（第十四届）《中国机械500强研究报告》发布会。首先，请允许我代表中国机械工业企业管理协会，向在百忙中参加本次发布活动的各位领导、嘉宾、企业及媒体朋友们表示衷心的感谢!向进入《中国机械500强》的食业和107家进入《世界机械500强》的中国企业表示热烈的祝贺。

关键词： 非线性动力学   辛时间子域法   迭代法   变分原理   机械系统  

摘要： 建立了用于非线性机械动力响应分析的辛时间子域-迭代法.首先,在任一时间子域内,将原非线性动力方程分解为线性和非线性两部分.对于线性方程,采用基于相空间非传统Hamilton型变分原理的辛时间子域法求解.将线性响应代入非线性项并视其为载荷,重复使用辛时间子域法迭代求解至一定精度,各解叠加即得原方程在当前时间子域的数值解.然后,将这个时间子域的末端值作为下个时间子域的初始值,进行下一个时间子域的计算,如此递推下去直到最后一个时间子域.结果表明,该方法具有较高的计算精度和计算效率.

关键词： Cordierite   Mechanical activation   Non-isothermal kinetics  

摘要： The non-isothermal kinetics of cordierite formation from both non-activated and mechanically activated kaolinite + talc + alumina ceramic system was studied by differential thermal analysis (DTA). The mixture of kaolinite, talc and alumina was activated mechanically in a planetary mill, while amorphisation in the kaolinite, talc and alumina structure was studied by X-ray diffraction analysis. The activation energies depending on the conversion for cordierite formation were calculated from the DTA curves by using the non-isothermal method of Coats and Redfern at heating rates of 5, 10, 15 and 20 A degrees C min(-1). The mechanical activation of the kaolinite, talc and alumina mixture resulted in the decrease in activation energy values for cordierite formation.

关键词： Fischer-Tropsch synthesis   Kinetic   Cobalt catalyst   Iron catalyst   Model discrimination   Least squares  

摘要： Various reaction rate equations have been proposed for Fischer-Tropsch synthesis (FTS) for both iron and cobalt based FTS catalysts, and recently one generalized kinetic model has been developed for the mentioned catalysts. In this paper the new rate equation based on generalized kinetic (REGK) and 35 previously proposed rate equations were statistically evaluated and investigated, based on a large number of gathered kinetic data points for iron and cobalt based FTS catalysts. Among all the previous equations it was found that only REGK has general applicability as well as minimum error. Statistical investigations indicated that CO dissociation cannot solely be direct for both iron and cobalt based FTS catalysts. Also it was found that the effect of H-2 and CO2 inhibition is not significant for cobalt and iron based catalysts respectively. For iron catalyst, assumption of H2O as inhibitor was either not significant or not practical. In addition, it was demonstrated that water gas shift can directly affect FTS besides the effect on partial pressures. According to the obtained new results the generalized mechanism was further developed. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Metallic glass   Viscosity   Mechanical relaxation   Anelastic   Physical aging   Structural relaxation  

摘要： In this work, the mechanical relaxation dynamics of Fe55Cr10Mo14C15B6 metallic glass is explored by mechanical spectroscopy. The temperature-dependent loss modulus EaEuro(3)(T) shows the features of beta relaxation well below glass transition temperature T (g). This beta relaxation can be well described in the framework of anelastic theory by a thermal activated process with activation energy of 165 kJ mol(-1). Structural relaxation, also known as physical aging, has a large effect on the glass properties. The activation energy spectrum of structural relaxation is characterized by differential scanning calorimetry measuring the heat flow difference between as-quenched and relaxed states. The obtained energy spectrum is well described by a lognormal distribution with maximum probability activation energy of 176 kJ mol(-1). The obtained activation energy of structural relaxation is similar to that of beta relaxation observed from mechanical spectroscopy. Both values are also close to the Johari-Goldstein beta relaxation estimated by the empirical rule E (beta) = 26RT (g).

关键词： Composites   dynamic compression   mechanical properties   damage   delamination  

摘要： The in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction.

关键词： FIBROUS composites   HYGROTHERMOELASTICITY   MECHANICAL properties of polymers   NATURAL fibers   THERMOPLASTIC composites   FINITE element method  

摘要： The exposition of thermoplastic composites reinforced with natural fibers to moisture and heat is likely to lower their mechanical properties and restrain their use in the design of parts. The present work is focussed on investigating the effects of hygrothermal aging on the mechanical behaviour of injected polypropylene reinforced with short hemp fibers. Moreover, the kinetic of isothermal moisture absorption has been studied for four immersion temperatures. The experimental results show that the time taken to reach saturation decreases significantly with increase in immersion temperature. These tests also reveal that moisture absorption in this type of materials does not follow Fick's law. Thus, a new model is proposed to predict this behaviour by the use of a variable coefficient of diffusion. This model is implemented using both analytical and finite element analysis (FEA) approaches. The results obtained with this new model show a very good correlation between experimental, analytical, and FEA absorption curves. (C) 2015 Society of Plastics Engineers

关键词： NdMg12 alloy   Mechanical milling   Activation energy   Hydrogen storage   Kinetics  

摘要： In order to improve the hydrogen storage kinetics of NdMg12-type alloy, the Mg in the alloy was partially substituted by Ni, and mechanical milling technology was used to fabricate the nanocrystalline and amorphous NdMg11Ni + x wt.% Ni (x = 100, 200) alloys. Effects of Ni content and milling time on the gaseous hydrogen storage thermodynamics and kinetics of alloys were investigated systematically. The structures of as-cast and milled alloys were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscope (HRTEM). The pressure-composition isotherms (P-C-T) and the hydrogen absorption and desorption kinetics of the as-milled alloys were measured by an automatically controlled Sievert's apparatus and a differential scanning calorimetry (DSC) (SDT-Q600) with a H-2 detector. Thermodynamic parameters (Delta H and Delta S) for the hydrogen absorption and desorption of alloys were calculated from Van't Hoff equation. Hydrogen desorption activation energy of alloy hydride was also estimated by using Arrhenius and Kissinger methods. It is found that the variation of Ni content brings on a slight effect on the thermodynamic properties of the alloys, but it significantly improves the hydrogen absorption and desorption kinetics. The improved gaseous hydrogen storage kinetics of alloys are considered to be ascribed to a decrease in hydrogen desorption activation energy caused by increasing Ni content and prolonging milling time. (C) 2016 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.