压-剪复合应力波作用下材料动态断裂韧性研究

提出亚微秒单脉冲应力波载荷作用下Ⅱ型裂纹的平板冲击实验技术 .加载率为dK dt～ 10 8MPa·m1 2 ·s-1.实验中由锰铜应力片和弹性波理论分别测定和计算了压应力 ;通过微观分析确定了动态裂纹的平均扩展长度 ;引进等效应力强度因子 ,用动态断裂理论确定了 6 0 #钢的动态断裂韧性KⅠd和KⅡd ;建立了亚微秒冲击载荷作用下确定材料动态断裂韧性的方法     

单侧摩擦约束夹杂物的瞬态弹性波散射的时域边界元分析--反平面情况

应用时域边界元法研究了瞬态SH波对单侧摩擦约束夹杂物的散射问题.假设摩擦遵守库仑定理,当入射SH波足够强时界面会出现局部滑移.发展了一种有效的迭代技术以确定边界上的未知区域(滑移和粘着区).算例计算了无限域中圆柱埋置夹杂物对瞬态SH波的散射问题.     

直流反应磁控溅射在氮化的蓝宝石衬底上制备AlN薄膜

通过直流磁控反应溅射装置,在蓝宝石(0001)衬底和氮化的蓝宝石(0001)衬底上成功制备了氮化铝(AIN)薄膜.利用X射线衍射仪、原子力学显微镜和双光束扫描分光计,研究了蓝宝石氮化对AIN薄膜结构、应力、晶粒尺寸、形貌和光学性质的影响.X射线衍射研究表明:制备的AIN薄膜具有较强的(0002)择优取向,蓝宝石衬底的氮化不仅能够改善AIN结晶质量,而且还可以减少薄膜的残余应力.但是,原子力学显微镜结果表明:在蓝宝石衬底上制备的AIN薄膜的晶粒大小分布比在氮化的蓝宝石衬底上制备的AIN薄膜的晶粒大小分布更加均匀.我们认为,蓝宝石衬底在氮化的过程中形成的AIN具有过多的位错和缺陷,正是这些位错和缺陷造成了在氮化的蓝宝石衬底上制备的AIN薄膜的晶粒大小分布的不均匀性.吸收光谱显示:蓝宝石衬底的氮化并没有对AIN薄膜的光学性质产生明显的改善.     

"三明治"靶型在间接驱动冲击波实验中的应用

间接驱动方式具有提供更高冲击波压力的潜力,对冲击波物理研究来说是一种很好的驱动方式.针对间接驱动下X射线离化对透明窗口造成的致盲问题,提出了新的"三明治"靶型结构,以完成间接驱动下冲击波实验.该靶型可以用两种方法避免致盲效应对实验的干扰.一种方法是从时间上避开致盲效应,使致盲效应与冲击波测量区错开,从而获得冲击波数据.另一种方法是从强度上屏蔽X射线,将X射线阻挡在透明材料之前,使其不能产生致盲效应.对单冲击实验而言,用增加烧蚀层厚度的方法,将X射线离化效应与冲击波信号从时间上错开,获得了蓝宝石和石英晶体中冲击波实验的结果.用增加阻挡层的方法,获得了间接驱动条件下石英晶体和聚苯乙烯材料中的冲击波实验结果.提出的"三明治"靶型,为间接驱动条件下状态方程和冲击波调速技术提供了技术支持. 关键词： 冲击波 光学诊断 离化效应 干涉仪     

波状膜层全角度偏振分束特性的分析

从能带结构和等频面两方面完整阐述了利用光子晶体实现全角度偏振分束的条件，分析等频面目的在于确保波矢的切向分量保持连续，采用时域有限差分(FDTD)方法模拟了高斯光束在波状膜层中的传播过程，通过对比TE模与TM模在0°—89°不同入射角情况下的振幅透射系数，理论上验证了波状膜层的全角度偏振分束效应. 关键词： 光子晶体 偏振分束 等频面     

8 mm回旋行波管和返波管的三折螺旋波纹波导色散分析

 三折螺旋波纹波导使TE11模和TE21模相互耦合,其色散曲线能够在宽频带内与电子回旋共振,因此需要对色散方程进行研究。提出了适合工程实用的行波模式和返波模式的色散方程,并对方程中的耦合系数进行了简化,误差在1%左右。利用CST软件的VBA语言对螺旋波纹波导进行建模和计算,根据模拟得到的传输特性曲线的特点,提出一种模拟方法,将模拟与理论计算得到的色散曲线作对比,误差在5%左右。     

Highly monodisperse crosslinked polymethylmethacrylate microparticles by dispersion polymerization

Highly monodisperse polymethylmethacrylate (PMMA) microparticles crosslinked with carboxylic group-containing urethane acrylates (CUA) were produced by simple dispersion polymerization in methanol solution. In contrast to conventional crosslinkers, the CUA employed as a crosslinker was excellent for maintaining the monodispersity of PMMA microparticles even at moderate crosslinker concentrations (to about 5 wt%). It was believed that the CUA helped form the monomer-swellable surface of primary particles, because of the structurally long tetramethylene oxide groups in the molecule. Carboxylic groups in the molecular backbone resulted in larger primary particles by increasing the solubility of the monomer mixture in the medium. Owing to these larger primary particles, the crosslinked PMMA particles showed lower polymerization rates than the linear ones during particle growth. However, at high CUA concentrations (about 10 wt%), bimodal distributions were observed. This was attributed to the high crosslinking density of the primary particle surfaces. Therefore, monomer diffusion toward the polymer phase was restricted, resulting in more favorable secondary nucleation in the medium. Received: 12 May 1998 Accepted: 19 August 1998     

Multiple bond migration with participation of a protophilic agent

The pathways of migration of the multiple bond in propene and propyne molecules involving the hydroxide ion were investigated by theab initio (RHF/6-31+G^* and MP2/6-31+G^*) methods. Stationary points corresponding to stable complexes between the molecules under study and the hydroxide ion and between corresponding carbanions and water molecule were found on the potential energy surfaces of the proton transfer reactions. In the presence of hydroxide ion, migration of the multiple bond can occur by an “intramolecular” mechanism of the proton transfer involving the proton of hydroxide ion bound in the complex with propene or propyne molecule. For the propene system, such a mechanism seems to be quite realistic and more preferable energetically than a traditional two-stage mechanism with a passage of the proton into the medium. For the system with the triple bond, an equal expenditure of energy is required to follow any mechanism (without taking into account the effects of solvation and the interaction with a cation), whereas the formation of the stable [H₂C=C=CH·H₂O]⁻ complex can prevent further transformations. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 35–41, January, 1999.     

Wave propagation in saturated ground using the volume fractions

The purpose of this paper is to study the dynamic behavior of soft ground including a porous layer by considering the porosity change. In order to take the porosity change into account, the concept of the volume fraction, which has been proposed in continuum mechanics, is introduced. The constitutive equations presented by Bowen are applied to the analysis of the porous media. According to Bowen's theory, the porosity is considered as a variable called the volume fraction and has its own constitutive equation. The constitutive equation of the volume fraction has thermoelastic equation coefficients and is determined by the strains of the solid and the fluid. This means that the compressibilities of the solid and the fluid are considered. When the special condition is assumed, Bowen's theory can contain Biots's theory, which has been applied in earthquake engineering. The wave propagation in the ground including a porous layer, modeled by Bowen's theory, is studied and compared with that of Biot's theory. One-dimensional attenuation and surface amplitude are calculated. The effect of the volume fraction is discussed with respect to the compressibilities of the solid and the fluid.     

表面熔化

对近年来人们十分关注的表面熔化问题,从理论和实验上进行了综述性讨论。综述了一些金属晶体、冰及石墨吸附Ａｒ膜表面熔化的特征及其热力学理论解释。评述了半导体Ｇｅ（１１１）表面熔化的独特性质。