关键词： aluminium-graphite powder system   mechanical alloying   carbon to Al4C3 transformation   compacting   microstructure parameters   mechanical properties   indentation hardness   creep characteristics  

摘要： A method of mechanical alloying process is described. Carbon transformation to Al4C3 is characterized within the different heat treatment schedules and nine commercial carbon powders are tested. The micromechanism of carbon incorporation into the metallic powder, and its compacting are described. The influence of dispersed carbides on mechanical properties is evaluated together with the influence of deformation on microstructure and properties. It was proved that the transformation efficiency of carbon to Al4C3 by heat treatment of aluminium with the porous furnace black and electrographite is higher than that of the hard cracked graphite. Microstructure changes consisted of the fracture processes and welding of the particles with incorporation of C phase and forming of final granules. The dispersed phase Al4C3 particle size was measured on thin foil structures, and it was constant and as small as 30 nm. The particle size was influenced neither by the carbon type nor by the heat treatment technology applied. Subgrain size measured in the range of 100 grains in thin foils depended on the carbon type, as well. It ranged from 0.3 to 0.7 mu m. Using a DSI (depth sensing indentation technique), the Martens hardness, indentation modulus E and deformation work W for Al matrix and Al4C3 particles have been measured. The temperature dependence of ductility, and reduction of area in the temperature range of 623-723 K and strain rate of 10(-1) s(-1), indicated a considerable increase of these properties. In a case when the volume fraction of Al4C3 changes from lower to higher, the grain rotation mechanism dominates instead of the grain boundary sliding. The comparison of the tensile test results and changes in fracture for the Al-Al4C3 system at two temperatures and two strain rates is summarized. The dependence of the minimum deflection rate on the applied force as well as the dependence of the time to fracture on the applied force for two temperature levels (623 and 723 K) b

关键词： Machinery dynamics   n-DOF global model   Reconfigurable manufacturing systems (RMS)  

摘要： Automated model generation and solution for motion planning and re-planning of automated systems will play an important role in future reconfigurable manufacturing systems (RMS). An n-DOF Global Kinematic Model (n-GKM) was previously developed for any combination of either rotational or translational type of joints. In this paper, the automatic generation of the dynamic equations for the n-GKM is presented. For the symbolic calculation of the n-GKM dynamic equations, the recursive Newton-Euler algorithm is employed using the symbolic algebra package MAPLE 12. The dynamic model is named Global Dynamic Model (n-GDM). The significance of the n-GDM is that it automatically generates each element of the inertia matrix A, Coriolis torque matrix B, centrifugal torque matrix C, and the gravity torque vector G, using Automatic Separation Method (ASM). The n-GDM is a dynamic solver for the n-GKM which includes predefined reconfigurable parameters. These parameters are used to control the joint's positive directions and its type (rotational and/or translational). Instead of solving the dynamics of different kinematic structures, the n-GDM can be used to auto-generate the solution by only defining these reconfigurable parameters. Using n-DOF Global Dynamic Model equations, a 3-DOF Global Dynamic Model (GDM) is derived. The 3-GDM has been validated using five selected cases (RR, RT, TR, TT planar and SCARA configurations). The results show the model ability to automatically generate different dynamic realizations for any required configuration. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

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： molecular dynamics   polyethylene (PE)   semicrystalline   mechanical properties   elasticity  

摘要： We present results from molecular dynamics simulations for an all-atoms model of a semicrystalline polyethylene under uniaxial tensile test. Our model has a realistic semicrystalline organization of two high molecular chains which are involved in two crystalline and two amorphous phases. The tie-molecules link these phases. A high content of tie-molecules is compatible with the stability of the semicrystalline organizations in the initial state. The main objective of the study is to check the effect of some molecular parameters, poorly known from experiments, on the mechanical properties under uniaxial tensile test. It is a way to have an insight on the value of the probable molecular parameters. We show that the number of tie-molecules mainly acts on the elastic modulus and the lamellar thickness acts on the yield stress. A nearly constant stress, a plateau, results from the narrow length-distribution of tie-molecules. This plateau is not observed during mechanical experiments. This plateau is the direct result of isomolecular tie-molecules. The only way to predict the progressive increase of the stress up to the yields stress observed experimentally is to consider a large length-distribution of tie-molecules. This progressive increase of stress implies a progressive deformation of the crystalline phase. The basic mechanism of plastic deformation is the pull-out of crystalline chain segments by the tie-molecules in extended conformation. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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。