高蓄光粉体应力与光蓄性恢复研究

制备了Sr4Al1 4 O2 5:Eu2 +、Dy3+,其发光衰减符合I =ct-n规律 ,具有高蓄光特性。但研磨后 ,随粉体细化发光强度急剧衰减 ;对研磨后的粉体进行退火处理及X射线应力分析 ,结果表明 ,退火后粉体的应力减小了 5 0 .1 % ,余辉相对强度大幅度提高。     

岩土本构关系的特殊性和统一性

在阐明岩土塑性变形的基本特殊性,特别是应力应变关系与应力路径相关性,产生机理的基础上,明确指出了导致这些特性的内在的共同的根源是,岩土塑性变形中存在两个相对独立的变形,即体积应变和剪切应变,两者之间存在着强烈的非线性的相互作用.这种耦合作用造成岩土的力学响应不仅具有多样性和复杂性,而且也具有内在的统一性.     

空间滤波与图像锐化技术在质量检测中的应用

介绍了中值滤波的非线性和在去除图像噪声但能保持边缘不被破坏的特点以及图像锐化技术对图像微分作用后，抽取图像轮廓，对感兴趣的图像特征进行识别的过程．利用这些技术加以综合，对工业产品的表面进行质量检测．     

复杂应力状态下混凝土强度理论研究

混凝土的强度理论是土木、采矿和水利等众多混凝土工程中的安全性和稳定性设计的重要基础理论。对它进行研究具有重要的意义．为此，在双τ^2屈服准则的基础上，建立了两参数双τ^2强度理论，给出了材料的极限强度比，从而说明了不同的材料对应着不同的强度理论．其次，利用两参数双τ^2强度理论分析了混凝土的脆性破坏，并同某些混凝土的实验数据进行了对比，最后，讨论了中间主应力效应，结果表明，运用两参数双τ^2强度理论分析混凝土强度的结果是令人满意的．     

基于双Haar小波的边缘检测

边缘检测在计算机视觉中起着非常重要的作用 .但是现有的一些边缘检测方法对噪声非常敏感 .因此 ,如何得到更好的边缘检测方法受到了人们的重视 .近年来 ,作为一种新的工具 ,小波变换在信号处理中得到了广泛应用 .本文基于双Haar小波 ,提出了一种新的信号边缘检测算法 .与传统方法相比 ,有效地克服了脉冲噪声的影响 .     

Fracture analysis of a functionally graded coating-substrate structure with a crack perpendicular to the interface - Part II: Transient problem

In Part I of this paper, the static problem of a functionally graded coating-substrate system with an internal or edge crack perpendicular to the interface has been studied. In this part, the transient response of the structure is considered under an in-plane impact. Laplace and Fourier transforms are applied to reduce the mixed boundary value problem to a singular integral equation which is solved in the Laplace domain numerically. The dynamic stress intensity factors (DSIFs) are obtained by numerical Laplace inversion technique. The influences of material constants and geometry parameters on the dynamic stress intensity factors are studied. It is found that the DSIFs for an internal crack rise rapidly to a peak and then tend to the steady value without obvious oscillations, but the DSIFs for an edge crack have more obvious oscillations after rising to a peak with the increasing of the nonhomogeneity constant.     

Variations of stress intensity factor of a semi-elliptical surface crack subjected to mixed mode loading

Maximum stress intensity factors of a surface crack usually appear at the deepest point of the crack, or a certain point along crack front near the free surface depending on the aspect ratio of the crack. However, generally it has been difficult to obtain smooth distributions of stress intensity factors along the crack front accurately due to the effect of corner point singularity. It is known that the stress singularity at a corner point where the front of 3 D cracks intersect free surface is depend on Poisson's ratio and different from the one of ordinary crack. In this paper, a singular integral equation method is applied to calculate the stress intensity factor along crack front of a 3-D semi-elliptical surface crack in a semi-infinite body under mixed mode loading. The body force method is used to formulate the problem as a system of singular integral equations with singularities of the form r ⁻³ using the stress field induced by a force doublet in a semi-infinite body as fundamental solution. In the numerical calculation, unknown body force densities are approximated by using fundamental density functions and polynomials. The results show that the present method yields smooth variations of mixed modes stress intensity factors along the crack front accurately. Distributions of stress intensity factors are indicated in tables and figures with varying the elliptical shape and Poisson's ratio.     

Mixed numerical-analytical approach for dynamic one-point-bend test modelling

Specimen deformation during a one-point-bend impact test is modelled within 2D linear elasticity framework. Using modal superposition technique, the closed-form solutions for the striker force and dynamic stress intensity factor (DSIF) variation with time are derived. Parameters used in these solutions have been determined using plane stress finite element model of the specimen and approximated polynomially for a wide range of the specimen geometry parameters. The efficiency of the method proposed has been verified by comparison of the analytical results with the experimental data available in the literature and with the results of finite element analysis.     

Stokes flow past a swarm of porous circular cylinders with Happel and Kuwabara boundary conditions

The problem of creeping flow past a swarm of porous circular cylinders with Happel and Kuwabara boundary conditions is investigated. The Brinkman equation for the flow inside the porous cylinder and the Stokes equation outside the porous cylinder in their stream function formulations are used. The force experienced by each porous circular cylinder in a cell is evaluated. Explicit expressions of stream functions are obtained for both the inside and outside flow fields. The earlier results reported by Happel and Kuwabara for flow past a solid cylinder in Happel’s and Kuwabara’s cell model, have been deduced. Analytical expressions for the velocity components, pressure, vorticity and stresstensor are also obtained     

What failure analysis can do for the machine designer,operator, diagnostician,and prognostician

A competent failure analyst can often determine whether the machine design was nominally adequate with a half hour time slot for visual examination. The use of macrofractography, a specialized type of visual examination, can allow trained personnel to determine whether improper alignment or component imperfections may have contributed to an unexpected failure. Case studies will be presented. Some examples of “learning from the graveyard” and how that can facilitate improvements in design, manufacturing, and operations will be described. Reprinted with permission from Proceeding of the 58th Meeting of the Society for Machinery Failure Prevention Technology, April 2004, p. 329.