各向同性腐蚀法制备多晶硅绒面

本文介绍了一系列利用各向同性腐蚀法制备多晶硅绒面的试验，腐蚀液为硝酸和氢氟酸的混合溶液，添加了醋酸稀释液是为了降低反应速度。通过优化各种参数，获得了腐蚀速度平缓，适合工业生产的多晶硅绒面，绒面分布均匀。随着反应的进行，腐蚀坑由微裂纹状转变为气泡状，经反射率测定表明绒面达到了较好的减反效果。     

Crystallization and nematic–isotropic transition activation energies measured using the Kissinger method

The activation energies for crystallization in poly(3‐hydroxybutyrate) and for nematic–isotropic transition in liquid–crystalline polyesters have been calculated based on data obtained with a dielectric method and differential scanning calorimetry (DSC), respectively. This study explores the feasibility of using a modified Kissinger method to calculate the activation energies of these transitions. It has been found that the activation energy for crystallization in poly(3‐hydroxybutyrate) is 109 kJ/mol. The activation energy for nematic–isotropic transition in the liquid crystals is 487 kJ/mol. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2535–2537, 2001     

Elasto-plastic analysis of masonry with anisotropic plastic material model

This paper establishes an anisotropic plastic material model to analyze the elasto-plastic behavior of masonry in plane stress state.Being an anisotropic material,masonry has different constitutive relation and fracture energies along each orthotropic axes.Considering the unique material properties of masonry,a new yield criterion for masonry is proposed combining the Hill’s yield criterion and the Rankine’s yield criterion.The new yield criterion not only introduces compression friction coefficient of shear but also considers yield functions for independent stress state along two material axes of tension.To solve the involved nonlinear equations in numerical analysis,several nonlinear methods are implemented,including Newton-Raphson method for nonlinear equations and Implicit Euler backward mapping algorithm to update stresses.To verify the proposed material model of masonry,a series of tests are operated.The simulation results show that the new developed material model implements successfully.Compared with isotropic material model,the proposed model performs better in elasto-plastic analysis of masonry in plane stress state.The proposed anisotropic model is capable of simulating elasto-plastic behavior of masonry and can be used in related applications.     

无奇异完全各向同性2T1R型并联机构的结构综合

提出了无奇异各向同性三自由度2T1R空间并联机构结构综合的一种系统方法。得到了24种新型无耦合并联机构方案和24种完全各向同性并联机构方案。在整个工作空间内,完全各向同性并联机构的主动副速度与动平台速度之间的线性映射雅可比矩阵为3×3阶单位阵,因此机构不存在奇异现象。由于无耦合并联机构和完全各向同性机构实现了主驱动器与动平台速度的一一对应关系,从而解决了并联机构控制难的问题。给出了完全各向同性2T1R并联机构支路的构造设计原则。     

Controllability Conditions of Finite Oscillations of Hyper-Elastic Cylindrical Tubes Composed of a Class of Ogden Material Models

In this paper, the dynamic inflation problems are examined for infinitely long cylindrical tubes composed of a class of transversely isotropic incompressible Ogden material models. The inner surface of the tube is subjected to a class of periodic step radial pressures relating to time. The influences of various parameters, namely, the material parameters, the structure parameters and the applied pressures, on dynamic behaviors of the tube are discussed in detail. Significantly, for some given material parameters, it is proved that the motion of the tube would present a class of nonlinear periodic oscillations for any given pressures and the amplitude of oscillation is discontinuous for some special values of the given pressures. For other cases of material parameters, there exists a critical pressure such that the motion of the tube would also present nonlinear periodic oscillations if the given pressure does not exceed the critical value, however, the tube would inflate infinitely with the increasing time if the pressure exceeds the critical value. Finally, the case of periodic step pressures is considered and all controllability conditions for the finitely periodic oscillations of the cylindrical tube with time are presented by using the phase diagrams of the ordinary differential equation that governs the motion of the inner surface of the tube, especially for the neo-Hookean material, i.e., a special case of the incompressible Ogden material models. Meanwhile, some numerical examples are given.     

微机电系统中的材料和加工

本文主要讨论微机电系统中的常用材料和加工技术。具体分析了Ｓｉ、ＧａＡｓ、ＳｉＣ、金刚石和石英等材料的性能及其在微机电系统中的应用,并论述了材料的各向同性和各向异性刻蚀加工技术以及材料间的健合工艺。     

Plastic zones in a transversely isotropic solid cylinder containing a ring–shaped crack

In this study, a problem of a ring shaped-crack contained in a infinitely long solid cylinder of elastic perfectly-plastic material is considered.The problem is formulated for a tranversely isotropic matrial by using integral transform technique under uniform load. Due to the geometry of the configuration, Hankel and Fourier integral transform techniques are chosen and the problem is reduced to a singular integral equation. This integral equation is solved numerically by using Gaussian Quadrature Formulae and the values are evaluated for various for discrete points. The plastic zone widths are obtained by using the plastic strip model. They are plotted for various ring-shaped crack sizes and transversely isotropic matrials. It is found that the width of the plastic zone at the inner tip of the crack is greater than the outer one.     

基于SiO2掩膜层的硅基微半球谐振子模具加工工艺

微半球模具的三维对称性对半球谐振子的性能有着决定性的影响。提出使用热氧化工艺生长的SiO2材料作为掩膜层,以达到在使用HNA腐蚀溶液制作微半球陀螺谐振子模具的过程中加快纵向腐蚀速率及实现半球模具三维对称的目的。详细研究了不同腐蚀窗初始半径下HNA腐蚀溶液对〈111〉单晶硅进行纵向和侧向腐蚀时,其腐蚀深度和腐蚀速率的演化规律,并在此基础上通过设置适当的腐蚀窗初始半径(5μm)以及腐蚀时间(15 min),成功制作出了半径为38.937 7μm的三维对称半球谐振子模具,通过球度拟合证明该模具整体半径方差为0.789 3μm,球度偏差为2%,为半球谐振子三维对称性的提升奠定了基础。     

浅谈各向同性焦的生成机理及制备方法

各向同性焦与各向异性焦一样是炭素工业中的重要原材料,用其生产的炭素制品被广泛应用到机械、冶金、化工、半导体、核能、宇航等领域,本文简要叙述了各向同性焦与各向异性焦的差别,各向同性焦的生成机理及制备方法.     

微晶石墨制备各向同性石墨的研究

本文研究了以天然微晶石墨为骨料制备各向同性石墨材料的可能性,对比传统骨料发现,微晶石墨模压制备的样品具有较低的各向异性指数1.11,较高的体积密度1.73g/cm3及良好的力学性能。以微晶石墨做为骨料采用等静压成型时,样品的各向异性指数低于1.05。同时还研究了粒度配比、浸渍工艺、粘结剂含量对材料性能的影响。