关键词： Bead-spring model   Elongation   Elastic modulus  

摘要： The mechanical properties of an epoxy-based chemically amplified resists with various cross-linking ratios were simulated using a newly developed coarse-grained molecular dynamics simulation that employs a bead-spring model. Models with the different cross-linking ratios were created in the molecular dynamics calculation step and uniaxial elongation simulations were performed. The results reveal that the simulated elastic modulus of the resist modeled by the Kremer-Grest model with an extended angle bending potential depends on the cross-linking ratio, its dependency exhibits good agreement with that determined by nanoindentation tests. (c) 2012 Elsevier Ltd. All rights reserved.

关键词： MOLECULAR dynamics -- Simulation methods   POISSON'S ratio   DEFORMATIONS (Mechanics)   COMPOSITE materials   BOUNDARY value problems   STRAINS & stresses (Mechanics)   MATERIALS -- Mechanical properties  

摘要： A method based on “small-deformation mechanical response” has been developed to locally resolve the Poisson's ratio via molecular dynamics simulations. The approach can be used for simple and composite materials to characterize systems with two or more continuous phases in the framework of periodic boundary conditions. The proposed technique represents a simple method to obtain a local mechanical description of complex systems. A polystyrene bulk, a silica bulk, and a polystyrene-silica heterogeneous composite material have been characterized under imposed strain. The results show the effects of local material inhomogeneities which are present in the glassy material and in the composite system. The Poisson's ratio spatial profiles for silica, the polystyrene bulk, and in the interphase region between the soft polymer bulk and the hard surface have also been calculated. The obtained local mechanical description can be employed in micromechanical models developed to predict the overall mechanical properties of multicomponent materials.

关键词： Amorphous materials   Metallic glasses   Computer simulations   Atomic scale structure   Clusters  

摘要： We present results on the microstructure of Cu-Zr metallic glasses (MGs) at equilibrium and under tensile deformation by means of large scale molecular dynamics (MD) simulations and density functional theory (DFT) calculations. We found that the MGs are composed by interpenetrating icosahedral-like (ICO) clusters forming superclusters (SCs). The deformation accommodation is associated with the destruction and recreation of these ICO clusters and SCs. DFT calculations on the Cu13Zr10 SCs with Cu-Cu core atoms revealed the presence of a free of bonds (FoB) plane that could be viewed as analog of a slip plane of the crystalline materials. The microalloying (MA) effect in a similar SC (one of the core atoms substituted by Al) yielded that Al is associated with the formation of a FoB plane. These results provide possible explanations of the experimental findings referring to the short range order, the MA effect and could potentially be used for the design of new MGs. (c) 2011 Elsevier B.V. All rights reserved.

关键词： PP-RCT   Mechanical properties   Thermal degradation   Kinetic analysis  

摘要： Polypropylene-random copolymers are a relatively new type of polypropylene (PP) modified plastics, which were introduced over the last years on the market. The comonomer which is most commonly used is ethylene at random concentrations for the improvement of mechanical and thermal properties of the final material. For the present work, we characterized and compared the mechanical properties and the thermal degradation kinetics results of polypropylene-random copolymer (PP-R) with 7% ethylene content and polypropylene-random copolymer/enhanced crystalline structure/improved temperature resistance (PP-RCT), which is formed by using a special beta-nucleation process, which leads to a homogenous dispersion of equal sized beta-crystals. The tensile strength properties of PP-RCT are improved due to the presence of both alpha- and beta-crystals, making the final product more ductile than neat PP or its random copolymer (PP-R), which both consist exclusively of alpha-crystals (monoclinic system). Characterization with XRD and DSC confirmed the two crystalline phases of PP-RCT. Thermogravimetric (TG) studies of PP-RCT showed that the new material exhibits better thermal stability than neat PP-R, since 1% mass loss of PP-RCT appeared at temperatures 10 degrees C higher than neat PP-R. The activation energy of degradation of PP-RCT and PP-R was calculated using the Kissinger, Akahira and Sunose (KAS) method. Degradation took place into two stages;the first stage which corresponded to an initial small mass loss was simulated with an n-th order model (F-n), while the second stage was attributed to the main degradation mechanism of the material and was simulated with an n-th order model with autocatalysis (C-n). When the calculated activation energies with isoconversional and model-fitting methods are compared, PP-RCT has much higher activation energy than PP-R, a fact which indicates the higher thermal stability of PP-RCT. (C) 2012 Elsevier B.V. All rights reserved.

关键词： 科技成果鉴定   汽车起重机   国家级   机械   技术创新项目   中国科技会堂   中小型   自走式  

摘要： 2012年7月30日，愚公机械股份有限公司承担的山东省技术创新项目小型双动力自走式起重机（中小型双动力汽车起重机），在北京中国科技会堂顺利通过国家级科技成果鉴定。

关键词： 混合动力   客车   自动变速器  

摘要： 传统内燃机（ICE）为客车提供了良好的动力性能，并利用石油燃料高能量密度的优点可实现远距离或长时间的连续行驶。但传统内燃机排放不良气体，污染环境，且燃油经济性差。燃油经济性差的主要原因在于：发动机燃油效率特性与实际运行要求不匹配；车辆制动期间，车辆动能不能回收利用而被消耗掉，当车辆在市区内运行时尤其明显；对于频繁停车一起动运行模式的公交客车，内燃机车辆工作效率低、耗油高。

关键词： 热能动力   创新性   设计与制作  

摘要： 大学生创新项目的建设,对于来参加实验、实习的学生来说不仅提高了他们的创新意识、增加了创新能力,而且还加强了学生的实践经验,起到积极的作用。本文以《以热能为动力源的机械结构小车创新性设计与制作》项目为例,阐述了小车的设计与制作过程并加以讨论。

关键词： 农业   动力机械   更新发展  

摘要： 农业动力机械在农业生产中起到了一个重要的作用,降低农业生产中对劳动力、物力的要求,提高了农业生产力。农业动力机械的不断更新使农业得到了良好的发展,提高了农业生产效率,农业动力机械更新是农业技术的一个重要环节。文中对影响农业动力机械更新的各种因素进行探讨,探讨农业动力机械更新的发展方向,为以后的农业技术推广工作提供依据。

关键词： 并联机械腿   伺服电机   动力学分析   Lagrange方程   峰值预估模型  

摘要： 提出了一种结构紧凑、承载能力大、转动解耦性好、运动速度和加速度大的3自由度并联机械腿。为了对其进行驱动参数分析,对机械腿进行了动力学建模,并基于动力学模型进行了伺服电机峰值预估。首先,分析了腿部机构各构件的运动参数,采用Lagrange方程建立了动力学模型,得出了机构驱动力的显式解;接着,在机构动力学模型的基础上,建立了伺服电机驱动转速和驱动力矩的峰值预估模型;最后,通过给定一组结构参数和运动轨迹函数,得出了伺服电机驱动转速和驱动力矩随时间变化曲线,得到了机构的动力学特性,并验证了峰值预估模型的正确性。计算表明,3个伺服电机驱动转速的峰值分别为Nx=19r/s、Ny=17r/s、Nw=27r/s;3个伺服电机驱动力矩的峰值分别为εx=5.8N.m、εy=3.1N.m、εw=4.4N.m。

关键词： Fenestrated endovascular repair   AAA   FSI  

摘要： Fenestrated endovascular aneurysm repair (f-EVAR) stent grafts offer an alternative treatment for conventional open heart surgery for patients with juxsta-renal Abdominal Aortic Aneurysms (AAA) that are unsuitable for the common infrarenal endovascular aneurysms repair (EVAR) procedure. The f-EVAR endograft includes branched stent grafts fixed to the aortic endograft main body via designated strengthened fenestrations. Repetitive stresses activated upon the endograft by the pulsatile flow might cause detachment or fracture of branching. Thus, investigation of the flow forces and stresses on the graft may help minimize complications and improve the endograft design. The present work investigates the flow and stress fields of the fenestrated endograft configuration using a fluid structure interaction (FSI) model in order to evaluate risks for graft fracture or detachments. The results show that the f-EVAR dramatically improves the aortic and iliac flow and that elevated cyclic stresses are found at the graft's bifurcation and branches' connections. (c) 2012 Elsevier Masson SAS. All rights reserved.