EPO泡沫的静态压缩性能及其与EPS和EPE泡沫的比较

对EPO(发泡聚烯烃)、EPS和EPE泡沫进行截面泡孔结构、静态压缩试验以及使用性能比较。应力-应变曲线分析表明,EPO泡沫变形分为弹性段、塑性屈服平台段及致密段;由3者截面泡孔结构、应力-应变关系和缓冲系数-静应力关系的比较表明,EPO静态缓冲性能介于EPS与EPE之间,但与EPS更为接近;使用性能比较表明,EPO泡沫衬垫避免了EPS和EPE的缺点,集合了EPE柔软性、反复冲击性能好和EPS可模制成型的优点。     

The collapse of open sections under bending and compression

The nonlinear behaviour of beams of thin-walled open section under bending and compression is investigated experimentally and theoretically. Two collapse modes of a channel section are identified, which are shown to be dependent on the position of the applied forces in relation to the null points of the warping function. A simplified finite element formulation is shown to predict the behaviour in the plastic regime.     

Image Quality in Photographic Microreproduction

The importance of the different parameters determining image quality in photographic microreproduction is discussed. In a first section it is shown that the slope of the H. & D.-curve is limited, among other factors, by the modulation transfer function of the complete system. In a second section the relation between information capacity. resolving power and practical image quality is considered. It is shown that a linear combination of image spread and granularity provides a good criterion for image quality.     

实体模型图纸化转换中复合剖的实现方法

提出了通过建立浮动模块的方法，解决了实体模型提取正投影图时AutoCAD系统只能定义单一剖切面而不能定义多个剖切面的问题。笔者列举了提取模型复合剖视图时的各种问题，提出了浮动模块的概念。指出了它的作用、形式及特点，并通过实例说明如何利用浮动模块来构建和变换实体模型的结构与位置，以使复合剖切面单一化和剖切过程简单化。最后结合实例对创建浮动模块的方法和提取复合剖视图的过程作了详细说明。     

Determination of centers of flexure using the boundary element method

The center of flexure of a beam of an arbitrary cross-section can be shown to be given in terms of two harmonic functions which satisfy Neumann type boundary conditions. The problem is thus suitable for solution by the boundary element method. It is shown that the determination of the center of flexure can be carried out without resorting to area integrals once the values of the two harmonic functions on the boundary are known. Numerical examples are given for: semi-circular ring sections; an equilateral triangular section; and a right triangular section.     

Mechanism of decay of a jet into large drops

High-speed photography has shown that disintegration of a jet affects a single material cross section without reversible oscillations (contraction and expansion) in that section.     

Analysis of the load-carrying capacity of pressure vessels in the presence of through cracks

It is shown that the crack resistance of structural elements in the elastoplastic state is a function of the load on the weakened section and that elastoplastic fracture toughness can be characterized a set of critical values of a quantity calculated through the stress intensity factor (SIF). These values are correlated with a parameter that characterizes the elastoplastic strain of the theoretical section.     

Investigation of the properties of samples of lengthwise-extended shape using the velocity of propagation of an electromagnetic field

It is shown that the velocity of propagation of an electromagnetic field in samples of extended shape with a constant cross section depends on the structure of the sample material, its magnetic properties and, in particular, the viscosity, shape and dimensions of the cross section and the excitation frequency.     

The influence of initial stream turbulence on the characteristics of an axisymmetric immersed jet

Results are given of measurement of mean velocity and of velocity fluctuations in an axisymmetric immersed jet at various values of initial turbulence. It is shown that as the initial stream turbulence increases, the length of the entrance section decreases, and that the entrance section practically disappears in a strongly turbulent jet.     

To make a sapphire cone and lens

A procedure is illustrated which allows a combined cone and lens to be ground from sapphire. The cross section of this element of revolution is shown.     

Solutions of torsion crack problems of a rectangular bar by harmonic function continuation technique

A torsion problem of a rectangular bar with a crack perpendicular to the section contour is discussed (see Figs. 1–3). When solving the Dirichlet problem of the Laplace equation, we divide the original section into several rectangular regions, and using the Duhem theorem [1] (a theorem of continuation of harmonic function), the solution on original section can be found. The calculation of torsional rigidity is in a usual way. Using the compliance method, the K₃ is obtained. All numerical results are shown in Tables 1–6.     

The evaluation of two-dimensional carbon-carbon composite material by dynamic mechanical analysis

Carbon composite materials, consisting of carbon cloth densified with a carbon matrix, have been examined by dynamic mechanical analysis (DMA). Flat panel and conic section structures were investigated over the temperature range ambient to 500°C. Reproducibility of the calculated tensile storage modulus values has been shown to be within 5% at any one temperature over the entire temperature range. This technique, which has been demonstrated to be non-destructive of the sample analyzed, defines differences in mechanical properties of the composite material formed into a conic section by comparison with those of the same material formed into a flat panel. Minor heterogeneity has also been shown within a single conic section as well as differences between pitch and CVD matrix samples. A sample orientation effect was found with the conic section samples. Details of the experimental technique and assumptions made during calculation of the mechanical properties are discussed.     

复杂截面型材力控制拉弯成形数值模拟分析

复杂截面挤压型材的高精度拉弯成形是制造框架式车身的关键技术.本文基于动态显式有限元软件PAM-STAMP,针对一种典型的框架武车身用复杂截面挤压型材,对其力控制方式的直进台面式拉弯成形进行了数值模拟研究,对比分析了两种截面形状的型材截面畸变和回弹随补拉力增大的变形规律,并得到了摩擦系数对成形精度的影响.数值模拟结果表明,增加型材截面的变形刚度,可以显著地减小截面畸变和回弹;增加补拉力,增大了截面畸变但减小了回弹;增大摩擦系数,截面畸变量减小而回弹增加.     

Diagnostics of highly doped czochralski-grown silicon crystals

It is shown that effective diagnostics of strongly doped Czochralski-grown silicon single crystals in the initial (as-grown) state is provided by methods based on the interference phenomena of dynamic x-ray diffraction: the Lang section topography and the Borrmann effect diffractometry. The conditions of a test for the structural perfection of as-grown crystals, based on the observation of interference bands on the section topographs, are refined.     

Refinement of the Requirements Regarding the Errors When Measuring the Effective Scattering Cross Section of Objects Taking into Account the Operating Characteristics of the Detection Instruments

The basis for the requirements imposed on the error in measuring the effective scattering cross section is considered. It is shown that to ensure the same errors when calculating the detection range for different types of detecting instruments, the requirements imposed on the error of the effective scattering cross section need to be changed.     

Misalignment of Coaxial Conductors

Compressed gas insulated coaxial transmission lines are being developed which withstand 1200-kV rms phase-to-phase voltage and carry 3000 A continuous current. As a method of instrumenting the voltage on a single-phase of coaxial line, an isolated capacitive section approximately one meter in length is inserted between the conductors. The resulting displacement current due to line voltage is detected with low voltage electronics. In the present work, misalignment of the coaxial conductors is investigated theoretically and experimentally to determine the effect of small relative displacements on the amount of capacitance of the isolated section. Capacitance change due only to conductor misalignment is found not to restrict severely the metering accuracy of the isolated section, provided reasonable tolerances for the position of the isolated section are maintained. Forces due to imbalance of surface charge when the conductors are slightly misaligned are calculated and shown to be small, suggesting that a "voltage coefficient" of capacitance also should not severely restrict the metering accuracy of the isolated section.     

Strain energy release rates for a straight-fronted edge crack in a circular bar subject to bending

The strain energy release rate for a straight-fronted edge crack in a bar of circular cross section subjected to pure bending is determined. The cracked bar is modelled with two-dimensional plane-stress finite elements and strain energy release rates, determined from this model, are shown to be in close agreement with existing results for a bar subjected to three-point bending in which strain energy release rates were determined by measuring the compliance of the bar experimentally. The strain energy release rates for a crack in the circular cross section bar are found to be lower than those in a rectangular cross section bar having the same relative crack length and subjected to the same bending moment. Previously determined results for uniform tension are superimposed to obtain strain energy release rates for a circular cross section bar which is subjected simultaneously to a tensile load and a bending moment.     

Polarization distribution in a Gaussian beam reflected from a resonant medium

It is shown that the distribution of parameters of light polarization in the cross section of a Gaussian beam reflected from a resonant medium is substantially inhomogeneous. This inhomogeneity is especially pronounced in the wavelength range of light absorption by metals.     

The fracture of microscopic metal samples in a strong electrostatic field

The level of mechanical stresses arising in a conductor under the action of a strong electric field is evaluated. It is shown that the mutual repulsion of surface charges has to be taken into account for correct determination of the critical cross section.     

不规则I型和L型横截面形状薄壁杆件的横向弯曲稳定分析

根据势能驻值原理,采用转换B3样条函数模拟杆件横截面的翘曲位移场,文[8]提出了用于分析在横向荷载作用下薄壁杆件稳定问题的样条有限杆元法。方法适用于任意横截面形状和任意边界条件的薄壁杆件,考虑了杆壁中面上剪切变形的影响,能很好地描述剪力滞后现象。本文讨论了不规则I型截面简支梁和L型截面简支梁的屈曲分析,数值算例的结果表明了方法的灵活性、精确性和有效性。