液压平衡回路的研究

工程机械常用的液压平衡回路，存在着悬垂负荷再提升下滑和下降冲击、振动的问题。本文从出发，针对以上两问题作了原理上的分析，采用蓄能器记忆压力和补充油液，并用压力比较定时元件来控制提升与制动释放同步动作，为克服提供瞬间下滑，提出了简单、有效的解决方案。     

Composite beam–columns with interlayer slip—Approximate analysis

An approximate second order analysis procedure for composite beam–columns with interlayer slip subjected to transverse loading and axial compressive loads is developed. The magnification factors to be applied to the first order solutions in order to estimate the deflections and internal forces obtained by the second order analysis approach are presented. The method of applying magnification factors to internal axial forces is discussed. The approximate second order analysis procedure is developed for the four Euler cases with various transverse load conditions. The procedure is applied to and the accuracy is illustrated for simply supported partially beam–columns of steel and concrete, and timber and concrete with different bending stiffness and interlayer slip properties. The deflections and internal forces obtained by the approximate method compared extremely well, except for slip forces in case of very flexible shear connectors, with those obtained by the more rigorous second order analysis approach for different composite action (partial interaction) parameters (shear connector stiffness values). The study also shows that the magnification factor associated with the deflections can be utilized to estimate also the internal actions, except shear forces in case of very flexible shear connectors, in the second order case with minimal error for simply supported beam–columns. Thus, for members with shear connector stiffness of structural significance the proposed approximate method can be used in general for simply supported beam–columns. For other boundary and loading conditions, the approximate method needs to be re-evaluated. The approach of using one magnification factor greatly simplifies the analysis task for those components.     

The effect of temperature on gross slip fretting wear of cold-sprayed nickel coatings on Ti6Al4V interfaces

Fretting wear is an accumulation of damage that occurs at component interfaces that are subjected to high contact stresses coupled with low-amplitude oscillation. In metallic contacts, surface oxides, adhesion, and material transfer play a primary role in the initial stages of fretting wear degradation. Given these behaviors, the focus of this study was to determine the effect of temperature on inter-metallic fretting wear between Ti6Al4V (titanium, 6% aluminum, 4% vanadium) and cold-sprayed, commercially pure nickel coatings. The results presented herein show that increased temperature decreases friction through the formation of a uniform NiO layer, and by a reduction of Ni₂O₃ in contacts. In addition, it was found that a localized minimum friction coefficient is achieved at approximately 300 °C, above which friction increases slightly due to annealing of the cold-sprayed coatings.     

The choice of the optimum frequency band for correlation measurements of the time delay of steady signals

Algorithms for choosing the optimum frequency band for the correlation processing of steady signals are proposed and specific examples are considered. The particular features of the problem of filtering received signals for optimum and nonparametric detection algorithms are considered. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 55–61, November, 2008.     

Irrelevance of interface defects to heterojunction band offsets

We present a photoemission measurement of the valence band discontinuity, ΔE_v, and the Fermi level, E_F, position at the interface between different surface reconstructions of GaAs(100) and Ge. GaAs(100) exhibits a number of surface reconstructions that differ in their As content and bonding configuration. The initial and final Fermi level position is observed to move toward the conduction band as the As content of the starting surface increases. The observed change in the final E_F due to the variation in surface As content is 0.3 eV. The band offsets are the same (0.46±0.05) regardless of the starting surface. The addition of As during the interface formation causes the Fermi level position to further move toward the conduction bands of Ge and GaAs; however, it doesnot change the band offsets. We conclude that deposition-induced defects do not occur in sufficient density across the interface to play a primary role in determining the GaAs/Ge(100) heterojunction potential step.     

Geometrical imperfection and adiabatic shear banding

This work addresses the effect of small geometrical imperfections on adiabatic shear band (ASB) formation. The separate effect of the length and radius of short notches is systematically investigated in AM50 and Ti6Al4V alloys, using shear compression specimens. It is observed that the length of the imperfection does not influence ASB formation in these experiments. By contrast, the notch-root radius appears to be the dominant parameter for the two materials, in perfect agreement with the analytical predictions of Dinzart et al. [The catastrophic development of shear localization in thermoviscoplastic materials. J Phys 1994; IV(C8): 435–40]. The distribution of deformation energy over the gauge length is modeled numerically. The calculated average dynamic deformation energy levels are quite similar to those that are measured for the two investigated alloys. It is concluded that the global measure of the dynamic deformation energy provides valuable information about ASB failure from geometrical imperfections.     

鲤鱼钳毛坯楔横轧成形压力的工程计算

介绍了楔横轧成形过程的工艺参数及变形区参数，分析了楔横轧展宽区的金属变形情况及推导了变形区参数的工程计算公式。文末对鲤鱼钳毛坯进行了实例计算。     

Synthesis of poly(2,5-Thienylene Vinylene) and its derivatives: Low band gap materials for photovoltaics

Poly-(2,5-Thienylene Vinylene) (PTV) derivatives have been synthesised via the “dithiocarbamate precursor route” in good yield and satisfactory molecular weight. Structural characterisations of the conjugated PTV polymers reveal an optical band gap around 1.8 eV. Organic field effect transistors and organic based photovoltaic devices were made with the plain PTV, via a precursor approach. More specifically, solar cells were produced using a blend of the precursor PTV polymer and PCBM (1-(3-methoxycarbonyl) propyl-1-phenyl [6,6] C₆₁) at various ratios, converted in situ in thin film. A promising power efficiency of 0.76% was achieved.     

In_(1-x)Ga_xAs_yP_(1-y)/GaAs应变量子阱中电子和空穴能带的组分调制1

本文采用模型固体理论计算了In1-xGaxAsyP1-y/GaAs应变量子阱中电子和空穴的能带结构,研究了组分对能带的调制作用.结果表明,In1-xGaxAsyP1-y/GaAs量子阱的能带类型及带隙依赖于阱材料In1-xGaxAsyP1-y的组分。当y=1.0,x在0~1.0范围时,量子阱In1-xGaxAsyP1-y/GaAs的能带为类型Ⅰ;当y=0.6,x在0.32~1.0范围时,量子阱的能带为类型Ⅱ。即通过调整阱材料组分,可以方便实现这种量子阱的能带转型(即类型I-类型Ⅱ的转变)。     

35~#钢激光宽带淬火研究

利用扫描激光束对 35 # 钢材料进行了宽带激光淬火 ,在 3.0～ 3.3k W激光功率下 ,获得单道淬硬带宽15 mm,淬硬层深 0 .5 3mm。给出了不同激光功率条件下淬火区硬度沿淬硬层深的变化曲线 ,淬硬层硬度分布基本均匀 ,平均硬度约为 5 5 4～ 675 Hv,与基体硬度比较提高了 2 .3～ 2 .5倍。显微组织结构分析显示淬硬层沿层深方向可分为完全淬硬层、过渡层和高温回火区三个区域。