关键词： 合理选用   正确操作   日常维护   队伍建设  

摘要： 近几年,国际油价居高不下,使农业生产的成本增加,因此,合理选用动力机械,正确操作和使用、及日常维护显得尤为重要,所以,文章进一步提出加强农机队伍建设和农机具的管理也是必不可缺少的。

标准号: DIN EN ISO 11680-1-2012

关键词： 机械行业   工业化   国际经济环境   经济结构调整   宏观经济环境   全球经济   企业生存   经济运行  

摘要： 2012真的来了! 欧债危机持续发酵、全球经济增速放缓、国内物价高企不下、中小企业生存艰难……在国际经济环境复杂多变、国内经济运行呈现新态势的情况下，2012年将是中国经济发展的重要转型年。2012新年伊始，中央经济工作会议确立了稳中求进、加快经济结构调整的主基调。作为衡量一个国家工业化程度的重要标志，机械工业历来是整个国民经济的物质和技术基础，行业发展又与整个宏观经济环境密切相关。继往开来，

关键词： mechanical alloying in a ball mill   structure   Y2O3 and Fe2O3 oxides   deformation-induced dissolution of oxides   electron microscopy  

摘要： The kinetics of low-temperature dissolution of oxides Y2O3 and Fe2O3 in an iron matrix during mechanical alloying has been studied using electron microscopy. It has been shown that the dissolution rate upon deformation of primary coarse oxides Fe2O3 in alpha iron (and, hence, saturation of the alpha matrix with oxygen) during treatment in a ball mill for up to 10 h is several times higher than the dissolution rate of Y2O3 oxides. The high-temperature (1100A degrees C) annealing of a mechanoalloyed mixture of Fe + 1.5% Y + 1.35% Fe2O3 leads to the precipitation of 60% (of the total number of particles) secondary oxides 2-5 nm in size and only of 5-7% secondary nanooxides in a mechanoalloyed mixture of Fe + 2% Y2O3.

关键词： METALS -- Mechanical properties   COPPER-tin alloys   MOLECULAR dynamics -- Simulation methods   STRAINS & stresses (Mechanics)   DEFORMATIONS (Mechanics)   POLYCRYSTALS   POISSON'S ratio   SHEAR (Mechanics)  

摘要： This work aims at investigating the mechanical properties and behaviors of orthorhombic Cu3Sn crystals at room temperature through molecular dynamics (MD) simulation. The focuses are placed on the tensile stress-strain behaviors and properties of the Cu3Sn single crystal and also their dependence on applied strain and strain rate. An attempt to characterize the deformation evolution of the Cu3Sn nanostructure during the stress-strain test is also made. In addition, the elastic properties of bulk polycrystalline Cu3Sn are estimated, as a function of strain rate and applied strain, by using the monocrystal results. The effectiveness of the MD model is demonstrated through comparison with the nanoindentation results and also published theoretical and experimental data. The calculated orthotropic elastic and shear moduli and Poisson's ratio of Cu3Sn single crystal reveal not only high anisotropy, but also the great effects of applied strain and strain rate only as the strain rate exceeds a threshold value of about 0.072% ps(-1). Specifically, raising the strain rate increases the orthotropic elastic properties and also the ultimate tensile and shear strengths of the nanocrystal, whereas increasing the applied strain reduces them.

关键词： Silicon nanowires   nanomechanics   in situ electron microscopy   tensile   bending size effects  

摘要： Deformation and fracture mechanisms of ultrathin Si nanowires (NWs), with diameters of down to similar to 9 nm, under uniaxial tension and bending were investigated by using in situ transmission electron microscopy and molecular dynamics simulations. It was revealed that the mechanical behavior of Si NWs had been closely related to the wire diameter, loading conditions, and stress states. Under tension, Si NWs deformed elastically until abrupt brittle fracture. The tensile strength showed a clear size dependence, and the greatest strength was up to 11.3 GPa. In contrast, under bending, the Si NWs demonstrated considerable plasticity. Under a bending strain of <14%, they could repeatedly be bent without cracking along with a crystalline-to-amorphous phase transition. Under a larger strain of >20%, the cracks nucleated on the tensed side and propagated from the wire surface, whereas on the compressed side a plastic deformation took place because of dislocation activities and an amorphous transition.

关键词： Polylactide (PLA)   Material valorisation   Mechanical recycling   Thermo-mechanical degradation   Cold-crystallization   Segmental dynamics  

摘要： This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PIA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PIA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystallization during DSC and DMTA measurements, which enthalpy increased with each reprocessing step, suggested chain scission due to thermo-mechanical degradation. The effect of chain shortening on the glass-rubber relaxation studied by DMTA showed an increase in free volume affecting the segmental dynamics of PLA, particularly after the application of the second reprocessing step, in connection to the overall loss of performance showed by the remaining properties. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： 定义   排放   隔离器   机械   机械工程   管道   支承结构   试验   振动的传递   传输   振动   振动强度   振动测量  

标准号: BS ISO 18312-2-2012

关键词： 螺栓连接   定义   连接   机械振动   机械   机械工程   支承结构   试验   传输   振动   振动测量  

标准号: BS ISO 18312-1-2012

关键词： CHEMICAL kinetics   RESEARCH   OLEFINATION reactions   NUCLEAR magnetic resonance spectroscopy   LIGANDS -- Analysis   PALLADIUM catalysts -- Reactivity   CARBON-hydrogen bonds (Chemistry)  

摘要： Detailed kinetic studies and novel graphical manipulations of reaction progress data in Pd(II)-catalyzed olefinations in the presence of mono-N-protected amino acid ligands reveal anomalous concentration dependences (zero order in o-CF3-phenylacetic acid concentration, zero order in oxygen pressure, and negative orders in both olefin and product concentrations), leaving the catalyst concentration as the sole positive driving force in the reaction. NMR spectroscopic studies support the proposal that rate inhibition by the olefinic substrate and product is caused by formation of reversible off-cycle reservoirs that remove catalyst from the active cycle. NMR studies comparing the interaction between the catalyst and substrate in the presence and absence of the ligand suggest that weak coordination of the ligand to Pd prevents formation of an inactive mixed acetate species. A fuller understanding of these features may lead to the design of more efficient Pd(II) catalysts for this potentially powerful C-H functionalization reaction.