Electrical properties of EVA filled by zinc powder

Elastic composites of zinc powder directly dispersed within an EVA (ethylene-vinyl acetate) matrix were prepared by a hot plates procedure. Conductance of samples depends on the filler content in three different regimes: polarization, tunnelling effect and percolation. The surface corrosion was monitored by means of optical, SEM and EDX methods, and after that the loss of mass was checked. The corrosion only affects to the zinc particles placed of the surface of the composite samples.     

Electrical properties of epoxy resin filled with carbon fibers

The electrical properties of an epoxy resin filled with carbon fibers were studied. By discharging a high voltage through the composite it was found that the resistivity of the composite decreased. This effect was attributed to local dielectric breakdown of polymer layer between carbon fibers. The conduction mechanism of common and breakdown composites was studied by means of exploring of current-voltage characteristics and the frequency dependence of resistivity. A positive temperature coefficient (PTC) effect of resistivity behavior was observed both for common and breakdown samples.     

Gigacycle fatigue initiation mechanism in Armco iron

Microstructure irreversibility plays a major role in the gigacycle fatigue crack initiation. Surface Persistent Slip Bands (PSB) formation on Copper and its alloy was well studied by Mughrabi et al. as typical fatigue crack nucleation in the very high cycle fatigue regime. In the present paper, Armco iron sheet specimens (1 mm thickness) were tested under ultrasonic frequency fatigue loading in tension–compression (R = −1). The test on the thin sheets has required a new design of specimen and new attachment of specimen. After gigacycle fatigue testing, the surface appearance was observed by optical and Scanning Electron Microscope (SEM). Below about 88 MPa stress, there is no PSBs even after fatigue cycle up to 5 × 10⁹. With a sufficient stress (above 88 MPa), PSBs in the ferrite grain was observed by optic microscope after 10⁸ cycles loading. Investigation with the SEM shows that the PSB can appear in the body-centered cubic crystal in the gigacycle fatigue regime. Because of the grain boundary, however, the local PSB did not continually progress to the grain beside even after 10⁹ cycles when the stress remained at the low level.     

Electrical properties of hollow glass particle filled vinyl ester matrix syntactic foams

Low dielectric constant materials play a key role in modern electronics. In this regard, hollow particle reinforced polymer matrix composites called syntactic foams may be useful due to their low and tailored dielectric constant. In the current study, vinyl ester matrix/glass hollow particle syntactic foams are analyzed to understand the effect of hollow particle wall thickness and volume fraction on the dielectric constant of syntactic foams. The dielectric constant is found to decrease with increase in the hollow particle volume fraction and decrease in the wall thickness. Theoretical estimates are obtained for the dielectric constant of syntactic foams. Parametric studies are conducted using the theoretical model. It is found that a wide range of syntactic foam compositions can be tailored to have the same dielectric constant, which provides possibility of independently tailoring density and other properties based on the requirement of the application.     

不同直径炭黑环氧树脂基复合材料力电性能及其机理

通过实验研究了喷雾炭黑、 N762炭黑、 特导电炭黑和N326炭黑环氧树脂基复合材料的力电特性、 伏安特性及电场作用前后电阻变化, 以及炭黑掺量对其上述性能的影响。试验结果表明, 炭黑直径和掺量对炭黑环氧树脂基复合材料的力电特性、 伏安特性和电阻特性具有较大的影响。掺加质量分数为35％~52.5％, 直径123nm喷雾炭黑的环氧树脂基复合材料具有很好的力电性能, 电压和电流关系符合伏安特性, 施加电场前后电阻没有明显变化; 掺33nm特导电炭黑和30nm N326炭黑的环氧树脂基复合材料的力电变化没有明显的规律, 电压和电流关系不符合伏安特性, 施加电场后其电阻大幅度降低; 掺84nm N762炭黑和26.25％质量分数的喷雾炭黑的环氧树脂基复合材料力电变化具有规律性, 但不稳定, 电压电流关系不符合伏安特性, 施加电场后其电阻降低, 但下降的幅度不大。在实验研究的基础上, 建立了炭黑环氧树脂基复合材料电路模型, 揭示了电击穿是施加电场前后炭黑环氧树脂复合材料电阻发生明显变化的机理, 最后, 通过分析炭黑间环氧树脂间隙层的变形, 解释了炭黑环氧树脂基复合材料的力电特性变化规律。      

Electrical and rheological properties of PMMA/LDPE blends filled with carbon black

Conductive immiscible multiphase blends of PMMA/LDPE filled with carbon black (CB) were studied in this work. Thermo-electrical behavior of the blends was compared with the composites made up of individual polymers in the blend, PMMA and LDPE filled with CB. The conductivity of the immiscible binary blend at different CB content was followed and modeled using a model circuit in which resistors resembling different phases and the interface between them present in the blend. Electrical percolation threshold was measured for the blend and compared with the single component polymers in order to judge the preferred phase for CB distribution in it. Rheological network formation by CB particles in the blend was also studied using dynamic rheology. The effect of CB loading on the morphology of the multiphase blend was also studied using FESEM images. Theoretical models were also used to predict the percolation thresholds for electrical and rheological network formation and compared with the experimental values.     

Electrical,mechanical and thermal properties of polyvinyl chloride composites filled with aluminum powder

In this work, the electrical, mechanical and thermal properties of polyvinyl chloride (PVC) composites filled with different content of aluminum powder varying from 0 to 40 wt.% have been prepared. The dielectric properties of these composites were investigated in the frequency range 100 Hz–100 kHz at temperature range from 30 to 98 °C. The percolation threshold concentration, which is the concentration after which the conductivity increases many orders of magnitude with very little increase in the filler content for PVC/Al composites depends upon the measuring temperature, whether it is below or above the glass transition of the polymer matrix. The highest value of the electrical conductivity, σ, of the composites was found to be in the order of 10⁻⁸ S cm⁻¹, this value recommend such composites to be used in electrostatic dissipation applications as the range of conductivity for such application should be in the range of 10⁻⁵–10⁻⁹ S cm⁻¹.     

露天深孔爆破导爆管起爆网路盲炮事故树分析

为避免露天深孔爆破导爆管起爆网路产生盲炮,确保爆破施工安全,按照露天深孔爆破作业流程,通过分析导爆管起爆网路盲炮产生原因,建立了事故树模型。并在此基础上进行了定性分析,求出事故树最小割集为32个,最小径集为4个。得到了结构重要度排序,提出了盲炮事故预防的对策措施,可为类似工程的爆破设计、施工和安全管理提供参考。     

露天深孔爆破导爆管起爆网路盲炮事故树分析

为避免露天深孔爆破导爆管起爆网路产生盲炮,确保爆破施工安全,按照露天深孔爆破作业流程,通过分析导爆管起爆网路盲炮产生原因,建立了事故树模型。并在此基础上进行了定性分析,求出事故树最小割集为32个,最小径集为4个。得到了结构重要度排序,提出了盲炮事故预防的对策措施,可为类似工程的爆破设计、施工和安全管理提供参考。     

Bone repair of defects filled with a phosphocalcic hydraulic cement: an in vivo study

A quickly setting calcium phosphate-based hydraulic cement mixed with particles of tricalcium phosphate (TCP) ceramic was implanted in 56 metaphysial defects made in the long bones of ten adult mongrel dogs. Microradiography, histology and scanning electron microscopy (SEM) demonstrated the slow resorption of the cement and the bony incorporation of the calcium phosphate ceramic particles which were consistently embedded in bone. The original structural pattern of the bone tended to be restored 7 months after implantation. The cement did not hinder the incorporation of the calcium phosphate ceramic particles, neither did it elicit any inflammatory or foreign-body response. The cement was easily shaped and allowed a perfect filling of any defect, resulting in close contact of the whole implant surface with the host bone at the time of surgery, associated with appreciable mechanical strength. Most of the practical problems associated with the use of calcium phosphate ceramics in the repair of bone defects could be overcome with the cement.     

Electrical activity of extended defects and gettering of metallic impurities in silicon

Abstract

Electrical activities of slip dislocations and Frank type partial dislocations in Si were investigated using the temperature dependent electron beam induced current technique. It was found that both types of dislocation are recombination active in the temperature range below about 200 K only and inactive in the higher temperature range if they are free from decoration by metallic impurities. From the temperature dependence of the electron beam induced current contrasts, the energy levels of recombination centres on these dislocations were determined to be less than 0.1 ev. They are not accompanied by any deep levels. Debris of defects generated from moving dislocations has deep levels about 0.3-0.4 eV from the band edge even if there is no decoration with metals. Both slip dislocations and Frank partials become recombination active at high temperatures when they getter metallic impurities. The characteristics of impurity gettering by dislocations depend on both the species of impurities and the cooling rate of a Si crystal after contamination. As a result, the recombination activities of dislocations are influenced by a variety of external parameters.     

CFRP管面钻削缺陷形成机制

碳纤维增强复合材料(CFRP)传动轴因性能优越广泛应用于汽车、航空航天、船舶、冷却塔风机等轻量化领域,但其钻削过程中容易出现毛刺、分层等缺陷。为了揭示CFRP管面钻削缺陷形成机制,选择双锋角钻头和三尖二刃钻对CFRP管面钻孔,利用分步钻削盲孔和通孔的方法,分析了损伤部位的受力情况,揭示了入口撕裂、出口毛刺和分层产生原因。根据实验结果,发现双锋角钻头钻孔时入口撕裂损伤较大,损伤位置在钻头与管面接触最低点,且主要是那部分水平缠绕CFRP管的纤维,原因是水平缠绕的纤维屈曲变形最大,对切削力更加敏感。双锋角钻头和三尖二刃钻的横刃对孔最终出口分层没有影响,主切削刃的切削行为决定孔最终出口分层。相同钻头钻孔时,轴向力不是唯一影响分层因子的因素,还需考虑切削热。相比双锋角钻头,三尖二刃钻因锋利的外缘尖角能有效划断纤维,使出口分层较小。     

聚芳基乙炔树脂基复合材料固化缺陷的产生机制

针对石英纤维增强聚芳基乙炔(PAA)树脂基复合材料固化微裂纹缺陷问题, 采用差示扫描量热、 红外光谱、 顶杆示差、 三点弯曲及金相分析等方法, 通过PAA树脂的固化反应、 收缩特性分析, 研究了树脂浇注体力学性能、 增强体结构形式、 纤维体积分数对裂纹缺陷产生的影响。结果表明, PAA树脂固化收缩率大、 树脂脆性是PAA复合材料中裂纹缺陷产生的主要原因, 提高纤维含量、 减少富树脂区有助于抑制裂纹缺陷, 并且采用酚醛树脂对PAA进行改性后, 亦可有效减少裂纹的产生。      

初始缺陷对FRP加固混凝土柱破坏形式的影响

通过理论分析、有限元软件模拟以及试验验证来研究初始缺陷对碳纤维增强复合材料(Carbon FiberReinforced Plastics,CFRP)加固混凝土圆柱的力学性能和破坏形态影响。从宏微观角度定性分析初始缺陷对加固混凝土柱力学性能的影响;通过数值模拟与实验结果的对比,分析了轴压和偏压作用下带有初始缺陷的CFRP加固混凝土柱力学性能;研究了包裹层数、截面尺寸因素影响下的临界缺陷值的变化规律,论证了初始缺陷尺寸的改变对破坏形式的影响。     

Chain mechanism for initiation of hydrocarbon oxidation reactions in a low-temperature plasma

A self-consistent model is used for a numerical study of the kinetics of plasma-chemical reactions initiated in a low-temperature gas-discharge plasma in an atmospheric-pressure CH₄O₂ mixture. An analysis is made of a chain mechanism for the formation of radicals in ion-molecular processes involving water and oxygen molecules, which can appreciably reduce the energy consumption needed to form the oxidation products. It is shown that under the conditions of a non-self-sustained, electron-beam-initiated, atmospheric-pressure discharge the energy consumption needed to produce methanol molecules may, at a few eV, be between four and fives times lower than that in a self-sustained discharge. Pis’ma Zh. Tekh. Fiz. 24, 40–43 (October 12, 1998)     

Study of the reinforcing mechanism and strain sensing in a carbon black filled elastomer

The mechanical and electrical properties of a styrene-butadiene rubber (SBR) matrix reinforced with carbon black, at various weight fractions were experimentally studied. Τhe electroconductive composites were used for strain sensing, under tension, by measuring together strain and electrical resistance. The storage and loss modulus decrement with strain were also investigated, on the basis of Payne effect, while a micromechanical model developed elsewhere was employed for the interpretation of the reinforcing mechanism of the composites examined.