Dependence of aerodynamic characteristics and flow pattern on surface structure of a baseball

In this report, the aerodynamic characteristics, such as lift and drag, of an official rubber baseball are studied experimentally by comparing the characteristics of a sphere having a smooth surface and those of spheres having different surface structures. In addition, the flow velocity distribution is measured quantitatively using the spark tracing method. From the obtained results, the flow patterns for these baseballs and the flow mechanism around a sphere have been clarified.     

Flying characteristics and flow pattern of a sphere with dimples

It is known that the flying characteristics of the golf ball is influenced by flying speed, rotational frequencies and the dimples, etc. In this study, the drag and lift acting on the test balls are measured using a three components loadcell by changing Reynolds number and the spin rate ratio, the number and the depth of dimples. And the flow around the balls is visualized by applying the oil film method and PIV in the stationary state. From these results, the aerodynamic drag and lift coefficients of the balls in the stationary and the rotational state are made clear.     

Some new developments in rubber reinforcement

The reinforcement of natural rubber provided by in-situ generated silica is compared with that obtained with anisotropic particles such as nanofibers of sepiolite. In addition, the effect of a dual loading is also investigated. Compared with networks filled with a single type of filler (sepiolite or in-situ generated silica), the samples containing two types of fillers display high modulus but less extensibility.     

A new paradigm for the molecular basis of rubber elasticity

The molecular basis for rubber elasticity is arguably the oldest and one of the most important questions in the field of polymer physics. The theoretical investigation of rubber elasticity began in earnest almost a century ago with the development of analytic thermodynamic models, based on simple, highly-symmetric configurations of so-called Gaussian chains, i.e. polymer chains that obey Markov statistics. Numerous theories have been proposed over the past 90 years based on the ansatz that the elastic force for individual network chains arises from the entropy change associated with the distribution of end-to-end distances of a free polymer chain. There are serious conceptual objections to this assumption and others, such as the assumption that all network nodes undergo a simple volume-preserving linear motion and that all of the network chains have the same length. Recently, a new paradigm for elasticity in rubber networks has been proposed that is based on mechanisms that originate at the molecular level. Using conventional statistical mechanics analyses, Quantum Chemistry, and Molecular Dynamics simulations, the fundamental entropic and enthalpic chain extension forces for polyisoprene (natural rubber) have been determined, along with estimates for the basic force constants. Concurrently, the complex morphology of natural rubber networks (the joint probability density distributions that relate the chain end-to-end distance to its contour length) has also been captured in a numerical model (EPnet). When molecular chain forces are merged with the network structure in this model, it is possible to study the mechanical response to tensile and compressive strains of a representative volume element of a polymer network. As strain is imposed on a network, pathways of connected taut chains, that completely span the network along strain axis, emerge. Although these chains represent only a few percent of the total, they account for nearly all of the elastic stress at high strain. Here we provide a brief review of previous elasticity theories and their deficiencies, and present a new paradigm with an emphasis on experimental comparisons.     

纳米填充硅橡胶超声干耦合特性*

针对工业超声无损检测领域干耦合材料种类匮乏,且声能透射率低的问题,论文在室温硫化硅橡胶基底材料中添加不同成份和配比的纳米颗粒,制备了不同种类的干耦合材料,给出了干耦合条件下超声波的传输模型,得到了声学传输规律,对比分析了干耦合材料种类、厚度、硬度、超声中心频率及载荷因素对声能传输特性的影响。搭建了声学特性测试实验平台,分别对添加氧化铝、铁和二氧化硅纳米颗粒制备的干耦合材料进行了测定,试验结果表明填充二氧化硅质量分数为5%时,所形成的纳米填充硅橡胶的声阻抗提高了13.5%,使用200kPa预载荷对试块测量时回波幅值提高了18.0%,具有良好的声耦合性能。可为实际超声检测时干耦合材料的制备及应用提供参考。     

"甲虫和橡胶带"问题新解

给出“甲虫和橡胶带”问题的一种简便的新解法.     

橡胶气球非线性特性的理论与实验研究

根据橡胶气球的热力学性能及门尼模型理论,推导出橡胶气球膜在充气与放气两个过程中受到的附加压强与气球半径的关系,并以此推导出不同半径气球内部的压强,以及两个相互连通的气球体积变化与内部压强的关系,理论结果与实验相吻合.将橡胶气球模型应用于简易气垫船研究,建立了气垫船运动模型,并利用实验结果对理论模型进行了修正.     

Ash characteristics in controlled diode laser pyrolysis of chlorinated rubber

This paper describes the effects of 60 W High Power Diode Laser (HPDL) beams on the removal of chlorinated rubber (CR) paint from concrete surfaces and the ash particles generated from this process. The physical characteristics, including shape and size distribution of the removed and collected airborne CR particles, down to a size of around 1 μm in diameter, were determined using optical microscopy and image analysis. The shape of the particles observed was highly irregular, displaying no symmetry. The size distribution of the collected particles was found to range between 1–2000 μm, with the maximum concentration being found between 29 and 60 μm. The chemical characteristics of the CR ash particles were investigated by means of ESEM and EDX techniques. From a comparative analysis, it was found that the concentration of chlorine within the CR material was significantly reduced after HPDL treatment. This, together with DTA/TGA results indicated a combustive degradation of the CR polymer through the interaction with the process gas, oxygen, and the laser irradiation. Also, a strong correlation between laser power and average particle sizes has been found, with higher powers generally producing larger particle sizes. Opposite effects have been found by changing the oxygen flow rate, with higher oxygen flow producing, on average, smaller particles. An interpretation of the combustion process, as well as a brief discussion on operational safety and environmental impact of the products is attempted.     

Boltzmann and the Art of Flying

One of the less known aspects of the work of Ludwig Boltzmann (1844–1906) is that he was an advocate of aviation, one of the most challenging technological problems at the end of the 19th century. Boltzmann followed the work of the flight pioneers Otto Lilienthal (1848–1896), Wilhelm Kress (1836–1913), and Hiram S. Maxim (1840–1916) closely, and in a lecture in Vienna in 1894 and in a article in a Viennese newspaper in 1896 he advocated the provision of financial support for research in this field. I discuss Boltzmann’s involvement in aviation, and his related correspondence with Lilienthal and Kress.     

具有迟滞非线性的金属橡胶隔振器参数识别研究

金属橡胶隔振器具有非线性的动力学特性,对这种迟滞阻尼隔振器进行建模研究,建立了参数有物理意义的动力学模型.根据单自由度性能试验,进行了有关参数的试验识别方法研究,应用能量法及最小二乘法将非线性方程组转化为关于参数的线性方程组,从而对金属橡胶隔振器参数进行识别.识别结果与实验结果有较好的一致性,识别结果也说明了结构参数对隔振器性能的影响. 关键词： 金属橡胶隔振器 动力学模型 迟滞非线性 参数识别     

The influence of pre-stressing on breakdown characteristics in liquid silicone rubber

Liquid silicone rubber (LSR) has increasingly been used as one kind of inner insulating material. Studies of space charge and its effect during pre-stressing and breakdown (BD) process in LSR were carried out. DC electrical breakdown field (BDF) of LSR specimens before and after DC electrical pre-stressing was measured. The space charge characteristics of LSR specimens under different DC electrical pre-stressing fields and that during the BD processes were measured by a pulsed electro-acoustic (PEA) method. It was found that the amount of homo space charges near electrodes increases obviously as a rising electric field is applied. Whether the polarity of BDF is the same as that of the pre-stressing field or not, the DC BDF of pre-stressed specimens is higher than that of specimens without pre-stressing. However, the pre-stressing does not show monotone and saturation effects, as generally occurs in the literature. In hetero BD experiments for example, with an increasing pre-stressing field, the DC BDF first increases up to 14.5% at the pre-stressing field of 25 kV/mm and then decreases. The influence of pre-stressing on the BD processes in LSR are discussed. The relationship between space charge and the DC BDF was related to the microstructure of nano-silica and LSR molecules.     

Study of stress-strain characteristics of SBR and blended NR/SBR rubber

The effect of temperature and carbon black (CB) on the mechanical characteristics of styrene-butadine rubber (SBR) and natural rubber (NR) was studied at various temperatures. The relation obtained between true stress and true strain for both types of rubber showed three regions at room temperature and two regions at high temperature. The optimum CB concentration was found to be 95 phr for the unblended samples as it increases the stiffness of the SBR rubber materials at a maximum value. It was also found that the addition of NR to SBR increases the elasticity in the plastic region. The activation energy at the fracture of SBR samples decreased from about 2.7×10^–20 to 1.8×10^–20 J while for the blended samples NR/SBR it increased from 8×10^–20 to 10.1×10^–20 J with increasing CB concentration.     

Improvement in characteristics of natural rubber nanocomposite by surface modification of multi-walled carbon nanotubes

We aim to develop high-level applications of NR through the innovative use of multi-walled carbon nanotubes (MWCNTs) to improve reinforcing performance and thermal resistance. In this study, we examined the structures and characteristics of composite materials in which NR was the matrix and MWCNTs were the fillers. We studied the properties of composites containing surface-activated MWCNTs with three different diameters. The results show that the reinforcing performance improves as MWCNT diameter decreases, while thermal resistance improves as we decrease the heat-treatment temperature. The latter occurs because adherence between MWCNTs and NR becomes stronger at lower heat-treatment temperatures. We also found that for practical applications, we need to control active sites on MWCNTs to balance adhesion against thermal resistance.     

A new contrast parameter for visualization of the cross-link density in rubber based on the dipolar-correlation effect

A new parameter for NMR mapping is suggested on the basis of the mean squared dipolar fluctuation (MSDF). The MSDF characterizes the relaxation mechanism due to ultra-slow dipolar fluctuations in liquids subject to local anisotropy of molecular motions. These fluctuations can be monitored on the time scale exceeding a few microseconds. In rubber materials, the MSDF is a function of the density of chemical cross-links strongly affecting (anisotropic) mesh chain fluctuations. Experimentally, the MSDF is determined from the attenuation curves of the quotient of the amplitudes of the stimulated and the primary echoes produced by the three 90 degrees radio-frequency pulse sequence. In order to evaluate the MSDF maps, the latter sequence was combined with the standard scheme of the magnetic field gradients providing a spatial resolution. The pixel values of the MSDF are "visualized" using grey shades related to the equidistant intervals covering the whole range of the measured values. The MSDF maps are demonstrated for the two composite samples. The first sample consists of a water filled tube in the middle part surrounded by high molecular mass polyisoprene (PI) in the outer part. The relaxation weighted spin density image of this sample is dominated by a water signal with PI producing a much weaker intensity. The MSDF map, on the contrary, enhances the relative intensity of the outer, PI, part while scaling the middle, water, part down to the level of noise. The second sample consists of the four rubber pieces with different cross-link density. This sample thus models an inhomogeneous rubber object. The MSDF map produces clear contrast for the relevant regions. The advantages of employing this kind of NMR mapping for a characterization of materials are discussed.     

Luminescence characteristics of new substituted coumarins

Fluorescence spectra at 298 and 77 K and phosphorescence spectra at 77 K have been measured for five new compounds. Fluorescence and phosphorescence quantum yields have been measured by comparison with a standard (8-methoxypsoralen). Phosphorescence lifetimes at 77 K have been found for 2-hydrazyl-3,4-cyclopentyl-14,14-dimethylpryanocoumarin (1.60 msec); 2-hydrazyl-3,4-cyclohexyl-7-methoxycoumarin (1.35); 3,4-phenyl-4′,5′-cyclohexylpsoralen (2.50); 4′-methyl-3,4-cycloheptylpsoralen (1.10); and 4′,5′-dimethyl-3,4-cyclohexylpsoralen (1.25). The basic channel of energy deactivation for 3,4-phenyl-4′,5′-cyclohexylpsoralen; 4′-methyl-3,4-cycloheptylpsoralen; and 4′,5′-dimethyl-3,4-cyclohexylpsoralen is radiative transfer. Energies of the lowest excited triplet states have been calculated using an INDO/S quantum-chemical method.     

生物能量传递新模型中的孤立子特性研究

从庞提出的新的生物能量传递理论出发,用Runge-Kutta方法和蛋白质分子的特征参数值对该理论的基本动力学方程进行了数值模拟,求出了孤立子在自由运动下、在相互碰撞时以及它在长时间运动后的特征.研究表明,在这些运动过程中,这个孤立子始终保持稳定状态.于是看到它能真正承担起在蛋白质分子传递生物能量的功能.从而从数值模拟的角度证明了新理论的可利用性.     

新型涡流管的制冷特性研究

以新型涡流管为研究主体,通过实验,研究涡流管操作参数对涡流管性能的影响。根据实验数据,分析改变温度压力等操作参数对涡流管能量分离效应的影响。试验结果表明:当提高涡流管进气温度,其冷热两端出气温度升高,但并不影响涡流管的制冷效率;增加涡流管进气压力会提高涡流管制冷效应,并在冷流率为0.2时效果最明显;制冷效率随节流阀开度增加而增加且最终趋于稳定,而制热效率则随节流阀开度增加而减小并最终趋于稳定。