On the environmental fracture of polymethylmethacrylate

Crack propagation of PMMA in some liquid environments is described for various testing conditions, such as fixed load, fixed displacement and monotonically increasing displacement. Fracture mechanics concepts have been used successfully in analysing the results. When continuous stable cracking is achieved, values of fracture toughness (R) for PMMA under these loading conditions are obtained as a function of crack velocity () using the method of Gurney and Hunt [11]. For crack velocities greater than 10^–2 mm sec^–1, the fracture toughness values in the environments are increased when compared with the corresponding air results. Unique relationships betweenR and have been shown to exist for cracking in ethanol and carbon tetrachloride.     

Mode III fracture of a magnetoelectroelastic layer: exact solution and discussion of the crack face electromagnetic boundary conditions

This paper develops a closed-form solution for anti-plane mechanical and in plane electric and magnetic fields in a magnetoelectroelastic layer of finite thickness. Explicit expressions for the stresses, electric fields, and magnetic fields, together with their intensity factors are obtained for the extreme cases for impermeable and permeable cracks. Solutions for some special cases, such as a magnetoelectroelastic layer with infinite thickness, are also obtained. Applicability of the crack face electromagnetic boundary conditions is discussed. It is found that the crack profile is important in obtaining the correct electromagnetic fields and their intensity factors. The stress intensity factor, however, does not depend on the crack face electromagnetic boundary condition assumptions.     

Micro- and nano-scale deformation behavior of nylon 66-based binary and ternary nanocomposites

The primary aim of this paper is to provide an insight on the effect of the location of organoclay on the micro- and nano-scale deformation processes in melt-compounded nylon 66/organoclay/SEBS-g-MA ternary nanocomposites prepared by different blending sequences. In addition, the deformation processes of the ternary nanocomposites were compared to the binary nanocomposites (nylon 66/organoclay and nylon 66/SEBS-g-MA) and neat nylon 66. The incorporation of SEBS-g-MA particles toughened nylon 66 markedly; but the flexural modulus and strength were both reduced. Conversely, the use of organoclay increased the modulus but decreased the fracture toughness of nylon 66. Nylon 66/SEBS-g-MA/organoclay ternary nanocomposites exhibited balanced elastic stiffness and toughness. Stress-whitening studies of the fracture surfaces in terms of gray level were also performed and an attempt was made to correlate the optical reflectivity characteristics with fracture toughness. It was concluded that the capability of SEBS-g-MA particles to cavitate was decreased by the presence of organoclay in the SEBS-g-MA phase, resulting in reduced toughening efficiency. The best micro-structure for toughness and other mechanical properties is thus to maximize the amount of exfoliated organoclay in the nylon 66 matrix rather than to have it embedded in the finely dispersed SEBS-g-MA particles.     

Advances in Vapor Pressure Modeling for Electronic Packaging

Two advanced techniques have been developed for modeling vapor pressure within the plastic IC packages during solder reflow. The first involves the extension of the "wetness" technique to delamination along multimaterial interface and during dynamic solder reflow. Despite its simplicity, this technique is capable of offering reliable and accurate prediction for packages with high flexural rigidity. For packages with low flexural rigidity, the new "decoupling" technique that integrates thermodynamics, moisture diffusion, and structural analysis into a unified procedure has been shown to be more useful. The rigorous technique has been validated on both leadframe-based as well as laminate-based packages. With high accuracy and computational efficiency, these dynamic modeling tools will be valuable for optimization of package construction, materials, and solder reflow profile against popcorn cracking for both SnPb and Pb-free solders     

温压用铁粉松装密度的优化粒级匹配试验研究

为提高温压用铁粉的流动性和松装密度，对典型粉末的粒度分布、流动性和松装密度进行了试验研究。结果表明，随温度的升高单一粒径粉体的流动性和松装密度均变差，而多粒级匹配粉末在120℃内基本保持不变，且粉体粒度分布对粉末的流动性和松装密度影响较大。通过正交试验优化了粉末的粒级匹配，获得了高松装密度的H1粉末，其流动性与国外粉W1相当，而松装密度比国外粉W1和国内粉N1分别提高了5．03％和8．99％。     

嵌入式OS-uClinux软件开发环境的建立及应用程序开发模式

本文介绍了在mcf5272嵌入式硬件开发板基础上如何移植uClinux操作系统以及开发用户应用程序的基本模式。     

在嵌入式Linux上实现JFFS文件系统

本文通过在嵌入操作系统uClinux上实现可读写JFFS文件系统的实例，介绍了在嵌入式系统中使用Flash芯片的方法。     

关于并行计算系统中加速比的研究与分析

着眼于并行计算中的加速比,重点讨论了几种通用的并行系统中的加速比模型,并且就它们各自的优点和不足进行了分析和说明,确立了它们之间的内在联系,最后结合并行系统中存在的其他因素,提出了未来加速比模型需要考虑的问题。     

基于CORBA的三层结构管理信息系统的原理及实现

研究了基于CORBA的实现管理信息系统的新方法,并对其实现方法、体系结构和关键技术进行了探讨。     

激光三角法位移传感器测头设计

本文以直射式激光三角测头为例,导出了满足Scheimpfiag成象条件下的待测面位移与象位移间的准确关系,作为仪器结构参数设计的基础,并对提高测量精度和实用性的各项改进设计进行了分析。