一种聚合物分散液晶菲涅尔波带片

利用波长为800nm,脉宽130fs的飞秒激光在镀铝膜的玻璃基片上刻蚀出波带环图案,然后用溶致相分离法将其制备成聚合物分散液晶菲涅尔波带片.用波长为632nm的He-Ne激光对聚合物分散液晶菲涅尔波带片进行测试,结果表明:随着电压的增加该样品具有良好的光电可控性,可以实现对焦点光强的调控.在沿光轴方向上,测试到的主焦点位置与理论计算值相差小于5%,且聚合物分散液晶菲涅尔波带片在160V电压时衍射效率为10.4%,接近理论衍射效率12.1%,表明了该设计的可行性.     

高陡度薄壁光学零件在位测量与评价方法研究北大核心CSCD

为了满足空气动力学要求,采用共形薄壁结构的整流罩或光学窗口成为未来高速飞行器的发展趋势。但是这类零件在加工过程中,切削力会随着轴向位置发生改变,一次加工难以达到精度要求,需要通过在位测量、补偿加工来控制切削力变化所引起的面形误差。以超精密车床作为运动平台,设计高陡度薄壁光学零件的在位检测系统,研究测点分布的优化算法,实现测量效率和测量精度的统一;建立热变形误差修正模型,提高高陡度薄壁光学零件在位测量的精度。针对某型高陡度薄壁头罩,通过在位测量为补偿加工提供指导,将头罩表面误差由峰谷比(peak-tovalley,PV)3.1μm控制到PV 0.7μm,将同轴度控制到1.02μm,满足光学系统的性能要求。     

高速铣削难加工材料时硬质合金刀具前刀面磨损机理及切削性能研究

采用涂层硬质合金刀具和细晶粒硬质合金刀具对超高强度合金钢(硬度＞50HRC、抗拉强度σb＞1.4 GPa)和马氏体不锈钢(硬度＞30HRC)等难加工材料进行了干式高速端面铣削试验;选择刀具寿命作为刀具切削性能的评价指标,利用X射线能谱仪和扫描电子显微镜分析了硬质合金刀具前刀面的磨损形态、磨损机理以及刀具的切削性能.结果表明:在难加工材料的高速铣削过程中,涂层硬质合金刀具主要失效形式为前刀面磨损,细晶粒硬质合金刀具主要失效形式为前刀面月牙洼磨损与剥落;2种刀具的主要磨损机理均为扩散磨损和氧化磨损.对细晶粒硬质合金刀具而言,在考虑刀具材料与工件材料适配性的基础上,必须利用合理的刃口强化处理来降低磨损初期的刃口微崩刃倾向.     

Measurement of Residual Stresses in Nuclear-grade Zircaloy-4(R) Tubes—Effect of Heat Treatment

Nuclear-grade Zircaloy-4(R) tubes are produced by a unique manufacturing process known as pilgering, which leaves the material in a work-hardened state containing a pattern of residual stresses. Moreover, such tubes exhibit elastic anisotropy as a result of the pilgering process. Therefore, standard equations originally proposed by Sachs (Z Met Kd, 19: 352–357, 1927; Sachs, Espey, Iron Age, 148: 63–71, 1941). for isotropic materials do not apply in this situation. Voyiadjis et al. (Exp Mech, 25: 145–147, 1985) proposed a set of equations for treating elastically anisotropic materials, but we have determined that there are discrepancies in their equations. In this paper, we present the derivation for a set of new equations for treating elastically anisotropic materials, and the application of these equations to residual stress measurements in Zr-4(R) tubes. To this end, through thickness distribution of residual stress components in as-received and heat treated (500°C) Zr-4(R) tubes was measured employing the Sachs’ boring-out technique in conjunction with electrochemical machining as the means of material removal, and our new equations. For both as-received and the heat treated materials, the axial and tangential residual stresses were significantly higher than the radial and shear residual stresses. The largest residual stress was the tangential stress component in the as-received material, showing a tensile value at the outer surface and a compressive value at the inner surface. At high values of von Mises equivalent stress, the principal directions of residual stress coincided with the principal axes of the tube for the as-received material, as well as for the material heat treated at 500°C.     

Modeling of EDM responses by support vector machine regression with parameters selected by particle swarm optimization

Electrical discharge machining (EDM) is inherently a stochastic process. Predicting the output of such a process with reasonable accuracy is rather difficult. Modern learning based methodologies, being capable of reading the underlying unseen effect of control factors on responses, appear to be effective in this regard. In the present work, support vector machine (SVM), one of the supervised learning methods, is applied for developing the model of EDM process. Gaussian radial basis function and ε-insensitive loss function are used as kernel function and loss function respectively. Separate models of material removal rate (MRR) and average surface roughness parameter (Ra) are developed by minimizing the mean absolute percentage error (MAPE) of training data obtained for different set of SVM parameter combinations. Particle swarm optimization (PSO) is employed for the purpose of optimizing SVM parameter combinations. Models thus developed are then tested with disjoint testing data sets. Optimum parameter settings for maximum MRR and minimum Ra are further investigated applying PSO on the developed models.     

Computing parallel curves on parametric surfaces

Generating parallel curves on parametric surfaces is an important issue in many industrial settings. Given an initial curve (called the base curve or generator) on a parametric surface, the goal is to obtain curves on the surface that are parallel to the generator. By parallel curves we mean curves that are at a given distance from the generator, where distance is measured point-wise along certain characteristic curves (on the surface) orthogonal to the generator. Except for a few particular cases, computing these parallel curves is a very difficult and challenging problem. In fact, only partial, incomplete solutions have been reported so far in the literature. In this paper we introduce a simple yet efficient method to fill this gap. In clear contrast with other existing techniques, the most important feature of our method is its generality: it can be successfully applied to any differentiable parametric surface and to any kind of characteristic curves on surfaces. To evaluate our proposal, some illustrative examples (not addressed with previous methods) for the cases of section, vector-field, and geodesic parallels are discussed. Our experimental results show the excellent performance of the method even for the complex case of NURBS surfaces.     

基于人因可靠性的数控加工中心安全管理模型分析

通过对数控加工中心(CNC)人因可靠性分析,阐述了人因可靠性对数控加工中心安全生产的影响,建立了人因可靠性评估模型,为数控加工中心安全生产管理中防治人为差错提供参考,进而提高数控加工中心的安全管理水平.     

Study of the recast layer of a surface machined by sinking electrical discharge machining using water-in-oil emulsion as dielectric

Electrical discharge machining (EDM) caused a recast layer to form at the machined surface of the workpiece. The characteristics of the recast layer have a great relationship with the type of dielectric. The research work in this paper aims to acquire a profound knowledge of the recast layers of a surface machined by sinking EDM using water-in-oil (W/O) emulsion as dielectric. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and micro hardness analysis were performed. The characteristics of the recast layer formed in W/O emulsion were investigated by comparing them with those of the recast layer formed in kerosene and de-ionized water dielectric. It was found that the recast layer formed in W/O emulsion exhibited larger surface roughness, thickness and micro hardness compared with that formed in kerosene and de-ionized water. Both carbide and oxide were detected in the recast layer formed in W/O emulsion whereas only carbide was detected in the recast layer formed in kerosene. Due to the higher supersaturation of gases in the melted material, the recast layer formed in W/O emulsion was found to possess more micro-voids than that formed in kerosene and de-ionized water.     

结构渐变的二维表面等离子体光栅光吸收器

设计了一种结构渐变的表面等离子体光栅光吸收器,采用二维时域有限差分法(2D-FDTD)对其吸收特性进行了详细的分析。结果表明,通过调整槽深、槽宽和墙宽,可以有效地降低反射率,提高其对光的吸收能力。由中心向两边适当地使槽宽线性增加,同时使墙宽线性减小,可以达到较理想的吸收效果。对于不同空间半峰全宽的入射光,反射谱线的形状有所不同。当入射光的空间半峰全宽较窄时,该吸收器对短波长光的吸收能力更强。当入射光的空间半峰全宽较宽时,该吸收器对长波长光的吸收能力更强。这种光吸收器有望在全光芯片中得到应用。     

位错型微机械可变光衰减器的研究

介绍了一种基于微机械技术实现的可变光衰减器,通过微电磁驱动器改变输入输出光纤之间的径向偏移量来调整衰减量。基于波导传输理论分析确定了器件的结构参量,并通过集成电路微细加工工艺实现了器件的制作和封装。测试结果表明,该可变光衰减器的插入损耗小于1dB,动态范围约35dB,工作电压小于5V,偏振相关损耗小于0.1dB,体积为20mm×15mm×8mm,有望为全光网提供一种低成本,高性能的光通信器件。