A crack perpendicular to and terminating at a bimaterial interface

Using dislocation simulation approach, the basic equation for a finite crack perpendicular to and terminating at a bimaterial interface is formulated. A novel expansion method is proposed for solving the problem. The complete solution to the problem, including the explicit formulae for theT stresses ahead of the crack tip and the stress intensity factors are presented. The stress field characteristics are analysed in detail. It is found that normal stresses {ie27-1} and {ie27-2} ahead of the crack tip, are characterised byQ fields if the crack is within a stiff material and the parameters |p _T | and |q _T | are very small, whereQ is a generalised stress intensity factor for a crack normal to and terminating at the interface. If the crack is within a weak material, the normal stresses {ie27-3} and {ie27-4} are dominated by theQ field plusT stress. This work was supported by the Swedish Research Council for Engineering Sciences.     

A nonlocal theory for brittle fracture

In this paper, a nonlocal theory of fracture for brittle materials has been systematically developed, which is composed of the nonlocal elastic stress fields of Griffith cracks of mode-I, II and III, the asymptotic forms of the stress fields at the neighborhood of the crack tips, and the maximum tensile stress criterion for brittle fracture. As an application of the theory, the fracture criteria of cracks of mode-I, II, III and mixed mode I–II, I–III are given in detail and compared with some experimental data and the theoretical results of minimum strain energy density factor.     

Semiclassical Limit of the Gross-Pitaevskii Equation in an Exterior Domain

In this paper, we study the semiclassical limit of the Gross-Pitaevskii equation (a cubic nonlinear Schrödinger equation) with the Neumann boundary condition in an exterior domain. We prove that before the formation of singularities in the limit system, the quantum density and the quantum momentum converge to the unique solution of the compressible Euler equation with the slip boundary condition as the scaling parameter approaches 0.     

飞行器跨声速气动弹性数值分析

将流体和结构运动方程分别构造为含子迭代的计算格式,发展了一种紧耦合气动弹性分析方法.其中流体计算的空间离散采用改进的HLLEW(Harten—Lax-van Leer-Einfeldt-Wada)格式. TFI(transfinite inter- polation)方法用于生成随结构变形的自适应多块动网格.利用所发展的方法,对-翼-身-尾气动外形,数值预测了马赫数在0.3-1.3范围内的气动颤振边界.并详细研究了时间步长、子迭代步数、初始流场、耦合方法、疏密网格对颤振计算结果的影响.     

Dislocation behaviours ahead of crack tip

In this paper, a unified mechanics model for dislocation nucleation, emission and dislocation free zone is proposed based on the Peierls framework. Three regions are identified ahead of the crack tip. The emitted dislocations within the plastic zone in the form of an inverse pile up are treated as discrete elastic edge dislocations. Between that zone and the cohesive zone immediately ahead of the crack tip, there is a dislocation free zone. With the stress field and the dislocation density field in the cohesive zone, respectively, expressed in the first and second Chebyshev polynomial series, and the opening and slip displacements in trigonometric series, a set of nonlinear governing equations are obtained which take into account for the interaction between the emitted dislocations and cohesive zone and the nonlinear interaction between sliding displacement and the opening displacement. After discretization, the governing equations are transformed into a set nonlinear algebraic equations which are solved with Newton-Raphson Method. The results of calculation for pure shearing and combined tension and shear loading after dislocation emission are given in detail. Finally, the process of dislocation nucleation and emission on a pair of symmetric slip planes of angle α with respect to the crack plane under pure mode I load is analysed. The equilibrium positions and the number of emitted dislocation are determined. Several possible competition behaviors of dislocation emission vs cleavage are revealed.     

冲击破碎高能推进剂的燃烧异常

为研究高能推进剂的冲击损伤状态对其使用安全性的影响,以爆轰波为加载手段,对NEPE推进剂试样进行冲击损伤。经扫描电镜观察和密度测量,冲击试样的基体材料和固体颗粒破坏严重,密度降低。热分析实验表明,损伤有利于试样中硝酸酯热分解的进行。密闭爆发器实验显示,损伤使燃烧速度加快。     

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDIES ON SYNTHESIS OF SILICA NANOPARTICLES USING MICROWAVE-INDUCED PLASMA CVD

1. Introduction1.1 Silica nanoparticles and synthesis methods Silica (SiO2) nanoparticles are widely used in industry asan active filler for polymer reinforcement, a rheologicaladditive in fluids, a free flow agent in powders, and anagent for chemical mechanical polishing during IC (inte-grated circuit) fabrication (Sniegowski & de Boer, 2000).Silica powder is also used for producing silicon carbide(Koc & Cattamanchi, 1998) or opaque silica aerosols (Leeet al., 1995). Many methods can …     

Adsorption of Methylene Blue on Montmorillonite

ABSTRACT

Adsorption of Methylene Blue ( MB) on Na-, Fe- and Al-montmorillonite suspensions at 298.15 K were studied. The effect of different exchangeable cation on the adsorption amount of MB was determined. The results show that methylene blue cations( MB⁺ ) replace Na? more easily than they do Fe³⁺ and Al^{3 +} The adsorption isotherms on the three montraorillonites were all of Langmuir type, except that the isouHerm of MB on Na-montmorillonite presents nonmonotonic curve at low surface coverage. The specific surface areas in suspension were calculated by( MB ^{3 +} )method, and Na^? is more effective to determine the specific surface area by MB method in suspension than Fe^{3 +} and A^{3 +} The discrepancy of the specific surface area measured by MB and BET method was discussed.     

On the Webster Scalar Curvature Problem on the CR Sphere with a Cylindrical-Type Symmetry

By variational methods, for a kind of Webster scalar curvature problems on the CR sphere with cylindrically symmetric curvature, we construct some multi-peak solutions as the parameter is sufficiently small under certain assumptions. We also obtain the asymptotic behaviors of the solutions.