基于CO2激光的微纳光纤熔接技术研究

为了解决微纳光纤之间的结构稳定性差的问题,使用CO_2激光作为加热源,加热两根重叠在一起的微纳光纤,并在显微镜下观察其熔接情况,最终将两根微纳光纤熔接成一根,而且熔接点的光纤表面光滑,直径均匀。通过CO_2激光加热的方法,实现了微纳光纤高质量的熔接,增加了微纳光纤之间的机械稳定性,使其更容易制作出纳米光子器件。     

金属板料单点增量成形厚度减薄率的预测与控制

金属板料单点增量成形过程中成形区域厚度减薄率过大是影响成形极限的一项重要因素,预测成形区域壁厚是控制减薄率的重要方法。选取1060铝板,对单点增量成形过程中的壁厚变形过程进行分析,利用Abaqus有限元分析软件,建立单点增量成形有限元模型,利用仿真结果拟合出精度较高的壁厚预测公式,分析工具头直径、层间距、进给速度、板料厚度、成形角度等工艺参数对减薄率的影响规律,并通过试验验证有限元模拟的正确性,并提出通过改变成形轨迹控制减薄率的方法。结果表明:拟合出的壁厚预测公式所求得壁厚值比正弦定理所求得的壁厚值更接近实验值;壁厚减薄率值随着工具头直径、成形角度和板料厚度的增大而增加,随层间距的增加而减小,进给速度对减薄率影响不显著,成形角度是影响减薄率的最重要因素;采用压入点均布的成形轨迹可有效减小减薄率。     

不同壳厚聚苯乙烯/氧化铈复合磨料的合成及其抛光特性

以表面带负电荷的聚苯乙烯(Polystyrene,PS)微球为内核,采用液相工艺合成不同壳厚的聚苯乙烯/氧化铈(PS/Ce02)核壳包覆结构复合磨料,并用透射电子显微镜、场发射扫描电子显微镜、激光拉曼(Raman)光谱仪、热重示差扫描量热仪和动态光散射仪等手段对样品进行表征.用原子力显微镜观察和测量抛光表面的微观形貌、轮廓及粗糙度,考察复合磨料壳厚对硅晶片热氧化层抛光性能的影响.结果表明,所制备的PS/Ce02复合磨料呈规则球形,粒径在200～250 nm,壳厚在10～30nm.化学机械抛光结果显示,PS/CeO2复合磨料对硅晶片热氧化层表现出良好的抛光特性,且复合磨料壳厚对抛光表面粗糙度和材料去除率具有较大影响.经壳厚为20 nm的复合磨料抛光后晶片表面在5μm×5 μm范围内粗糙度平均值和方均根值分别为0.196 nm和0.254 nm,材料去除率为568.2 nm/min.     

推拉式小车法制备单层硒化钨薄膜

为了提升单层硒化钨（WSe₂）薄膜的制备质量，在传统化学气相沉积（CVD）法制备的基础上进行改进，通过引入推拉式小车来制备单层WSe₂薄膜，从而构造出可以调控沉积区域、精确控制生长时间，并可实现快速降温的生长方式。采用光学显微镜和原子力显微镜来表征制备材料的尺寸、荧光强度、形貌结构等特性，证明了利用推拉式小车法可成功制备出高质量的单层WSe₂薄膜。推拉式小车法可以稳定制备大面积、高质量、单层的WSe₂薄膜，为其在信息、能源、生物等前沿领域的应用提供参考。     

发动机气缸内表面激光微织构工艺试验研究

应用激光表面微织构技术加工缸壁储油槽,可保证储油槽的形貌精度。激光微织构加工装置的工艺参数(激光器控制参数)主要有激光焦距、激光功率密度和脉冲重复次数等。建立了不同工艺参数下凹腔织构的三维形貌和二维剖面形貌图,分析了不同工艺参数对凹腔形貌参数的影响规律。实验结果表明,合适的激光焦距、激光功率密度和脉冲重复次数能使凹腔的表面织构形貌最佳。     

微铣刀在位制备方法研究

提出基于WEDG技术的微铣刀在位制备方法,将微铣刀的制备与使用结合起来,在同一台微细电火花加工机床上完成微铣刀的在位制备与在位铣削过程,可实现微铣刀的低成本高精度制备,同时避免微铣刀的二次装夹所造成的倾斜和偏心误差,提高微铣削整体质量。为验证基于WEDG技术的微铣刀在位制备工艺方法的可行性,基于自研μEM-200CDS2型双主轴三工位微细组合电加工机床平台,进行了微铣刀在位制备与在位铣削的实验研究。结合WEDG工艺特点对微铣刀进行材料选用与构型设计,实现了直径小于100μm、刃口锋利的D型微铣刀的制备,并利用所制备微铣刀在位铣削出最小壁厚小于20μm的一组薄壁结构。实验结果表明:基于WEDG技术的微铣刀在位制备方法在原理和技术上是可行的。     

不锈钢基压电厚膜微悬臂梁传感器的制作与测试

制备了不锈钢基底压电厚膜微悬臂梁传感器。利用精密激光加工技术制备了厚度为100μm的不锈钢微悬臂梁基底,由于不锈钢具有良好的导电性,可以作微悬臂梁传感器的下电极,采用模板辅助电雾化沉积技术在不锈钢微悬臂梁基底上制备了厚度为20μm的致密PZT厚膜,利用磁控溅射技术制备了30/200 nm厚的Ti/Pt上电极,最终形成了压电厚膜微悬臂梁传感器。多普勒激光测振实验表明,在20 V的激励电压下,压电厚膜微悬臂梁谐振频率为19 kHz。     

原子力显微镜测量杨木细胞特征参数

在微/纳米尺度下原子力显微镜已成为研究木质材料的重要工具。本文基于原子力显微镜对速生杨木细胞的特征参数进行测量。结果表明:利用原子力显微镜,完全可以在微/纳米尺度下对速生杨木的细胞形态特征进行测量;杨木细胞横截面的导管壁厚平均尺寸为2.230 μ m;木纤维壁厚平均为2.044 μ m,壁长平均为9.498μm;细胞外径平均为19.723 μ m。     

一种球形容器角变形和错边控制量的新计算法

一、前言JB1127—82规定角变形的控制量是其棱角高度e≤10mm。根据对角变形附加应力研究表明,这样控制是不合理的。原因是: (1) 角变形附加应力与球形容器的直径、壁厚大小有关; (2) 同一角变形e值,对不同直径和壁厚的球形容器所产生的附加应力不同;     

石英玻璃泡壳数控成形设备的研究

对气体放电灯用的石英玻管泡壳的成形工艺研究,电弧管泡壳吹制成形后,壁厚应均匀,所以在泡壳吹制之前应对玻管进行堆料,用窄火头使玻管的局部加热烧熔,并压缩玻管的长度,使壁厚加大,控制火头的移动速度和玻管推进的速度,两者进给速度成函数关系.同时介绍泡壳成形设备主要组成部分、有关参数的计算和自动控制系统设计.     

紫外飞秒激光泵浦氮气离子相干辐射

氮气分子在不同波长（中红外、近红外、紫外）强场飞秒激光的泵浦下,其分子离子在传播前向能够发出具有良好相干性的可见光波段的窄带辐射。在400 nm紫外飞秒激光的激发下,波长为428 nm和423 nm的相干辐射受到的关注较少,物理性质尚不明确。本研究对该辐射的偏振性质、气压和泵浦激光能量依赖关系进行了系统的测量。实验发现,该辐射的偏振与线偏振泵浦激光的偏振态保持一致,辐射强度随着气压和泵浦激光能量呈现出非线性的增加。利用基于密度矩阵的强场电离和能级耦合模型,对氮气分子在强场中的电离和相关离子能级在强场作用下的耦合进行了数值模拟研究。结果表明,在较大的激光强度范围内,氮气离子上能级$ {\mathrm{B}}^{2}{\mathrm{\Sigma }}_{\mathrm{u}}^{+} $和其离子基态$ {\mathrm{X}}^{2}{\mathrm{\Sigma }}_{\mathrm{g}}^{+} $之间,对应428 nm和423 nm的振动态之间总是能够形成粒子数反转,而且该反转对于激光参数具有鲁棒性,与实验观测结果一致。     

Effect of gate dimension on micro injection molded weld line strength with polypropylene (PP) and high-density polyethylene (HDPE)

As a defect of micro injection molding parts, weld line is unfavorable since it will influence the surface quality and mechanical properties of micro parts. Therefore, the investigation on the developing process of weld line would be a significant issue for improving the quality of micro injection molded parts. In this study, one injection mold with four micro tensile sample cavities was designed and constructed. Every cavity responses to various gate dimensions, which is marked as Gate $ {\text{Nr}}.1\left( {1.5 \times 0.1 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) $ , $ {\text{Nr}}.2\left( {1.0 \times 0.1 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) $ , $ {\text{Nr}}.3\left( {1.0 \times 0.05 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) $ , and $ {\text{Nr}}.4\left( {0.5 \times 0.1 \times 0.{\text{5mm}},{\text{width}} \times {\text{depth}} \times {\text{length}}} \right) $ . The effects of gate dimension of the mold on mechanical properties of weld line have been studied by experiments in different processing parameters. The tensile test was used to characterize the micro injection molded weld line strength. The results for polypropylene show that with the changing of injection pressure and mold temperature, Gate Nr.3 is corresponding to the strongest weld strength; the next is Gate Nr.2; Gates Nr.4 and Nr.1 are in the end. The difference between them is not obvious. For high-density polyethylene, Gate Nr.1 is not able to be completely filled, which is due to the blocking of stick materials and dirt based on the simulation analysis. The investigation was only carried out for the other three gate sizes; results present that Gate Nr.3 always gives the best weld line strength whatever the processing parameters are, Gate Nr.4 is next and then Gate Nr.2. There are always middle optimal values for processing parameters leading to strongest weld line strength, when injection pressure is 80 MPa, injection speed is 90 cm³/s, melt temperature is 200°C, and mold temperature is 130°C. Higher and lower processing parameters result in reduced weld line strength.     

Atmospheric effects of friction,friction noise and wear with silicon and diamond. Part III. SEM tribometry of polycrystalline diamond in vacuum and hydrogen

In this part III of a multi-part paper series, the results of additional SEM tribometric experiments are described, performed with polished, mostly C(100)-oriented polycrystalline CVD diamond film [PCD_C(100) vs. PCD_C(100)] counterfaces sliding in Torr and in 0.1–0.3 Torr partial pressures of pure hydrogen gas. These tests were completed under a 28 g (0.27 N) normal load, under standard and slow thermal ramping conditions at temperatures ranging from room temperature to 1000^°C. The friction data were examined per the computer logging and analysis techniques described in part I. The treatment of the data is similar to that of Si in part II: the maximum and the average coefficients of friction (MAX.COF and COF) and their ratios (the friction noise FN) are employed to measure possible lubricative interaction of the diamond surfaces with rarefied hydrogen. The results indicate that excited species of molecular hydrogen enter into tribothermally catalyzed reactions not only with Si but with PCD_C(100) surfaces as well. Similar to the behavior of Si, the most beneficial friction-reducing regime occurs in a temperature range just before the thermal desorption of adsorbates. The general magnitudes of MAX.COF, COF and the FN are significantly lower than those of the Si crystallinities, in both vacuum and . The wear rate of the PCD_C(100) film characteristic of the standard thermal ramping test procedure performed mostly in is around , in good agreement with the wear rate previously measured in vacuum for unpolished, fine-cauliflowered diamond films. The data indicate that smooth polycrystalline diamond is a significantly better bearing material for miniaturized moving mechanical assembly applications than Si. This revised version was published online in July 2006 with corrections to the Cover Date.     

The curved wall jet over a circular cylinder before the interaction of two opposing curved wall jets

A curved wall jet before the interaction of two identical curved wall jets over a circular cylinder was investigated experimentally. Using hot-wire anemometry, the mean velocity, Reynolds stresses, and high order moments of the fluctuating velocity were measured. The turbulent kinetic energy and shear stress budgets were evaluated using the measured data. The correlation coefficient, ${{\overline {uv} } \mathord{\left/ {\vphantom {{\overline {uv} } {u'v'}}} \right. \kern-0em} {u'v'}}$ , the normal stress ratio, ${{\overline {v^2 } } \mathord{\left/ {\vphantom {{\overline {v^2 } } {\overline {u^2 } }}} \right. \kern-0em} {\overline {u^2 } }}$ , and the principal direction of the Reynolds stress are presented. The effects of curvature and adverse pressure gradient on these diistributions are also discurssed. The turbulent kinetic energy and shear stress budgets in two regions before the interaction are analyzed in detail to illuminate the effect of the adverse pressure gradient on the turbulent transport.     

Plastic deformation depth modeling on grinding of gamma Titanium Aluminides

This work reports on the subsurface plastic deformation depth (PDD) as a result of grinding of γ-TiAl, where the effects of grit size and shape, workpiece speed, and wheel depth of cut were studied. A grinding model based on a stochastic distribution of the chip thickness was used to estimate the expected maximum normal force per grit ( ${F''_{n\:{\rm max}}}$ ), which was correlated to the PDD. It was found that the PDD shows a linear correlation with ${F''_{n\:{\rm max}}}^{0.5}$ . The results suggest that the indentation model is still valid for grinding if ${F''_{n\:{\rm max}}}^{0.5}$ is used as a PDD predictor variable instead of the total grinding force.     

An investigation on multistage bending of blank sheet into cylindrical tube by experiment and numerical simulation

In this paper, one pair of punch and die was employed to experimentally investigate the pure bending of blank sheet into cylindrical tube by multistage process. The investigated material was hot-rolled HSLA370 with the thickness of 2?mm. Numerical simulation was conducted on bending and springback with LS-DYNA solver. Results showed that multistage bending technique was an alternative way to produce cylindrical tubes. The sequence is described as $ {\text{Blank}}\,{\text{sheet}}\xrightarrow{{{\text{Multistage}}\,{\text{bending}}}}{\text{C - tube}}\xrightarrow[{{\text{Welding}}}]{{{\text{Squeezing}}}}{\text{O - tube}} $ . Gap width and roundness of C-tube (configuration like letter ??C??) were two dominant parameters to evaluate the bending performance. The effects of blank positioning on both of them were investigated by means of numerical simulation. Laser-welded tubes meeting roundness and the tolerance limit of diameter were produced. Simulation revealed that effective plastic strain along circumferential direction was much low, mostly ranging between 0.03 and 0.05. Severe thinning and shape defects were not observed in the finished tubes. A numerical model was developed and its effectiveness was verified by a comparison between the predicted results and the corresponding experiments.     

Optimal design of \overline {\text{X}} -control chart with Pareto in-control times

Economic control chart models usually assume that the time to occurrence of an assignable cause follows an exponential or Weibull distribution. This paper extends that to the Pareto distribution in order to investigate, in general, the effect on the economic control chart parameters like sample size, time between two successive samples, and the cost per unit time of the distributional assumption. The Pareto distribution arises as a limiting distribution of the waiting time for the number of new observations needed to obtain a value exceeding the greatest among “n” observations. It was found that the economic design of $ \overline {\text{X}} $ chart is greatly influenced by the distributional assumption. Using the cost model, the sensitivity analysis of the statistical economic design of the $ \overline {\text{X}} $ chart with respect to the parameters and costs is studied.     

Bicriteria scheduling of a two-machine flowshop with sequence-dependent setup times

A two-machine flowshop scheduling problem is addressed to minimize setups and makespan where each job is characterized by a pair of attributes that entail setups on each machine. The setup times are sequence-dependent on both machines. It is shown that these objectives conflict, so the Pareto optimization approach is considered. The scheduling problems considering either of these objectives are $ \mathcal{N}{\wp } - {\text{hard}} $ , so exact optimization techniques are impractical for large-sized problems. We propose two multi-objective metaheurisctics based on genetic algorithms (MOGA) and simulated annealing (MOSA) to find approximations of Pareto-optimal sets. The performances of these approaches are compared with lower bounds for small problems. In larger problems, performance of the proposed algorithms are compared with each other. Experimentations revealed that both algorithms perform very similar on small problems. Moreover, it was observed that MOGA outperforms MOSA in terms of the quality of solutions on larger problems.     

Atmospheric effects of friction,friction noise and wear with silicon and diamond. Part II. SEM tribometry of silicon in vacuum and hydrogen

Scanning electron microscope (SEM) tribometric data on polycrystalline silicon (poly-Si) vs. poly-Si, Si(100) vs. Si(100) and Si(111) vs. Si(111) interfaces, obtained in Torr and in 0.2 Torr partial pressure of hydrogen gas ( ) from room temperature to 850^°C, were performed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology described in part I of this paper series. The results indicate a highly beneficial friction- and wear-reducing regime within a relatively narrow thermal region. This desirable region coincides with some chemisorption of excited species of molecular hydrogen just before the mass thermal desorption of surface hydrides. These data represent the tribochemical equivalent of a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking in molecular hydrogen. The also exerts a moderating influence on the size of the friction noise at all test temperatures. However, the general level of friction beyond the beneficial thermal region is high. In parallel, the general wear rate of Si representative of the entire range of standard thermal ramping in both atmospheric environments is in the extremely high 10^-12m³/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude reduction in the wear rate over those measured under standard thermal ramping conditions. Although the results confirm previous findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microbearings and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen at surface temperatures between 100 and 300^°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

The use of generalized magnetic parameters for magnetic structural analysis and nondestructive testing

The results of studies regarding the dependence of the product of the coercive force and the initial magnetic susceptibility of a nickel single crystal with an intermediate orientation on the shear stress are analyzed. It is concluded that an increase in the aforementioned product for a nickel single crystal upon cold plastic deformation is due to refining of magnetic domains that is caused by formation of cells and subgrains within the single crystal. The tentative size of magnetic domains was determined based on the value of generalized magnetic parameter . The variations in the product and in the calculated dimensions of magnetic domains in polycrystalline nickel are analyzed using data reported by Kersten-Gottschalt. It was also shown that, the density of dislocations being constant, the generalized magnetic parameter is sensitive to changes in the sizes of nonferromagnetic inclusions, whereas in the case of small nonferromagnetic inclusions, an increase in the generalized parameter is due to an increase in the density of dislocations.Translated from Defektoskopiya, Vol. 40, No. 7, 2004, pp. 62–76.Original Russian Text Copyright © 2004 by Bida.