Investigation of surface modifications in ethylene propylene diene monomer (EPDM) rubber due to tracking under a.c. and d.c. voltages

In the present work, tracking phenomena has been studied with the ethylene propylene diene monomer (EPDM) material under the a.c. and d.c. voltages, with ammonium chloride/acid rain solution as the contaminant. It is noticed that the tracking time depends on the conductivity and flow rate of the contaminant. The physico-chemical analyses viz. wide angle X-ray diffraction (WAXD), thermo-gravimetric differential thermal analysis (TG-DTA) and the differential scanning calorimetry (DSC) studies, were carried out and it was concluded that the tracking process is a surface degradation process. The tracking time is different for a.c. and d.c. voltages.     

Preparation and characterization of nano-hydroxyapatite/silicone rubber composite

To take advantage of the merits for both hydroxyapatite (HA) and silicone rubber (SR) in medical applications, we developed a novel method to produce a new nano-composite of these two widely used biomaterials. In this work, n-HA (nano-hydroxyapatite) slurry, which was modified by silane coupling agent, was mixed with silicone gum and the nano-composite could therefore be achieved. It is found that the dispersion states of the n-HA particles in SR are homogeneous and the mechanical properties of the composite can be improved significantly. The composites with micrometer HA (μ-HA) and SR were taken as the contrast for comparison. We find that the tensile strength of the n-HA/SR composite can be enhanced greatly in comparison with that of the μ-HA/SR composite.     

Analysis of surface degradation of high density polyethylene (HDPE) insulation material due to tracking

In the present work, tracking phenomena has been studied with HDPE material under a.c. voltage, with ammonium chloride as the contaminant. It is noticed that the tracking time depends on the conductivity and flow rate of the contaminant. The diffusion coefficient of the material was obtained. The thermal and chemical stability of the material were identified by carrying out a methodical experimental study. The physico-chemical analyses viz. wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), were carried out and it was concluded that the mechanism of tracking process is due to the surface degradation. The surface condition of the insulation structure was characterized for any surface discharges or tracking, using the leakage current measurement, utilizing the wavelet concepts.     

Preparation of a novel type of flame retardant diatomite and its application in silicone rubber composites

A novel strategy was used for preparation of flame retardant based on biomass debris to improve the flame retardant property of silicone rubber (SR). [(6-oxido-6H-dibenz[c,e][1,2]oxaphosphorin-6-yl)methyl]butanedioic acid (DDP) was used to modify diatomite by esterification method, and DDP@diatomite was obtained. The structure and morphology of this novel additive was identified using Fourier transform infrared spectroscopy (FTIR), Brunner-Emmet-Teller (BET) measurements, and X-ray photoelectron spectroscopy (XPS) together with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDXS) techniques. Thermogravimetric (TG) analysis was performed to evaluate the thermal degradation behaviors of diatomite and DDP@diatomite. This novel additive was applied into silicone rubber (SR) composites. Combustion parameters, including heat release rate (HRR), total heat release (THR), smoke production rate (SPR), carbon monoxide (CO), peak smoke production rate (PSPR), peak carbon monoxide (PCO) and vertical burning time, were characterized by cone calorimeter and vertical burning tests. Results indicated that this flame retardant can reduce fire risk and toxicity effectively. TG and X-ray diffraction (XRD) patterns of SR and its composites were also investigated. The inexpensive property of modified diatomite could also expand its fire safe applications.     

双层结构纳米羟基磷灰石/硅橡胶复合材料的制备及性能

纳米羟基磷灰石/硅橡胶与硅橡胶在同时硫化的条件下制备出了双层结构的纳米羟基磷灰石/硅橡胶复合材料,利用XRD、SEM、MTT和力学性能测试等手段对复合材料进行表征.结果表明,两层材料的界面结合紧密,材料的细胞相容性好,力学性能与硅橡胶的力学性能相近,能够达到医用植入硅橡胶材料的要求.     

纳米功能化石墨烯/室温硫化硅橡胶复合材料的制备与表征

用KH-550对氧化石墨进行改性, 再对其进行还原, 获得功能化石墨烯(FG), 未经干燥的FG经超声处理后可以稳定分散在质量比9∶1的丙酮/水混合液中; 在高速搅拌和超声分散条件下, 将FG分散液分散到室温硫化(RTV)硅橡胶中, 固化后得到纳米FG(nano-FG)/RTV硅橡胶复合材料。采用FTIR、TEM、SEM、XRD和DSC分析了FG及复合材料的结构和形貌。结果表明: KH-550连接到石墨烯片层表面上, 使其片层起皱、折叠, 部分发生了剥离, 层间距增大到3.46 ; FG经过超声处理后剥离成透明至半透明的片层; nano-FG/RTV硅橡胶复合材料的断面结构为褶皱结构, 不同于纯硅橡胶, 也未出现微观相分离; 与硅橡胶相比, 复合材料的T_g、T_m和结晶度均有所提高。复合材料的力学性能测试结果表明, nano-FG对RTV硅橡胶具有明显的补强效果, 当nano-FG质量分数为0.5 %时, nano-FG/RTV硅橡胶复合材料的拉伸强度比纯RTV硅橡胶提高了一倍多, 达到了0.43 MPa; 断裂伸长率也提高了52%, 达到了265%。      

改性纳米SiO2/硅橡胶复合材料的制备及性能

为提高纳米SiO₂在硅橡胶（SR）基体中的分散性及两相间的界面结合力,设计以羟基硅油（HSO）和γ-甲基丙烯酰氧基丙基三甲氧基硅烷（KH570）为纳米SiO₂的表面封端改性剂,并将改性SiO₂与双组份加成型液体SR复合得到改性纳米SiO₂/SR复合材料。通过一系列表征手段对改性纳米SiO₂的形貌结构及其在乙醇中的分散性等进行分析,研究了改性纳米SiO₂对纳米SiO₂/SR复合材料的断面形貌、力学性能及热稳定性的影响。结果表明:KH570成功接枝到纳米SiO₂表面并与SR基体间形成化学键。当HSO协同KH570改性纳米SiO₂时,可有效改善纳米SiO₂在SR基体中的分散性能及纳米SiO₂与SR两相间的界面结合性能,并显著提高纳米SiO₂/SR复合材料的力学性能和热稳定性。将SiO₂∶HSO∶KH570以质量比为2.0∶0.2∶0.6处理的改性纳米SiO₂粒子,得到的改性纳米SiO₂/SR复合材料起始热分解温度提高了230℃。当SiO₂∶HSO∶KH570质量比为2.0∶0.2∶0.45时,改性纳米SiO₂/SR复合材料的拉伸强度和断裂伸长率分别提高了约1倍。      

炭黑的表面修饰及其对炭黑/硅橡胶导热性能的影响

通过采用羟基硅油对炭黑表面修饰, 改善炭黑与硅橡胶之间的相容性, 从而减小炭黑与硅橡胶界面热阻, 制备了高导热系数炭黑填充硅橡胶, 研究了炭黑填料与硅橡胶的相容性及炭黑/硅橡胶的导热系数。结果表明: 与原炭黑/硅橡胶体系相比, 经过羟基硅油修饰的炭黑与硅橡胶的相容性得到明显改善。当经表面修饰炭黑的质量分数为36.59%时, 表面修饰炭黑/硅橡胶的导热系数可达到0.591 W·(m·K)^-1, 较同含量未修饰炭黑/硅橡胶的导热系数高38.7%。     

Characterization of the protective effect of aluminium surface treatments by d.c. and a.c. measurements

Steady-state and electrochemical impedance spectroscopy measurements have been made on anodic layers on 1050 and 2024T3 aluminium alloys prepared from solutions of phosphoric acid, boric acid and sodium tetraborate, before and after impregnation treatment with zinc. Corrosion characteristics of the anodic layers were dependent on the aluminium substrate and the electrolyte. Aluminium alloy composition was found to be the most important factor for corrosion resistance; alloying elements of 2024T3 alloy (like copper) had a harmful influence on this layer property. Steady-state measurements allowed the oxide layer behaviour to be studied in the anodic range by the determination of an anodic passivity domain. This domain was characterized by a weak aluminium oxidation through the oxide layer. The zinc impregnation treatment had a marked protective effect on each studied anodic layer. This treatment can be used as an alternative to hot sealing in water or chromic acid solution.     

基于响应面法橡皮成形侧压块参数优化及验证

橡皮成形是飞机钣金零件制造的一种重要的成形工艺,为提高典型零件橡皮成形的效率,针对橡皮成形过程中产生的起皱问题,基于响应面法对侧压块参数进行优化.首先对新淬火状态下的铝合金板料进行材料试验,分析了其成形性能指标参数,为有限元模拟提供材料本构关系与模型;然后以起皱量化为优化目标,将凸弯边的最大增厚率作为侧压块优化的目标函数,为得到典型零件橡皮成形侧压块精确的几何参数,采用Abaqus有限元软件对带侧压块成形过程进行正交模拟试验,得出侧压块几何参数对起皱指标影响程度的主次关系,并得到最优的参数水平组合.基于响应面建模方法建立了侧压块最优几何参数和起皱指标之间的多项式关系,并用遗传算法进行参数优化,利用优化后的工艺参数进行有限元模拟,阐述了侧压块防皱原理;最后通过实际成形试验,验证了有限元模拟的可行性和优化方法的可靠性.     

Synthesis and characterization of silicon nitride powders produced in a d.c. thermal plasma reactor

Ultra-fine silicon nitride powder was synthesized from the SiCl₄-NH₃-H₂-Ar system using a d.c. plasma torch reactor (production rate 150–400 g h⁻¹). The powder produced is pure white, fluffy and amorphous. The particles are spheroidal in shape with a mean diameter between 30–60 nm forming aggregates of 0.1–0.4 μm depending on the operational conditions. Chemical analysis on the crude powder handled at ambient atmosphere revealed: N(−NH₄Cl):37–39%, O:3–5% and Cl:2–3%. The amorphous powder can be crystallized around 1500 °C under nitrogen to give an α-phase content in excess of 90%. Infrared spectra can be used to semi-quantitatively determine the NH₄Cl content of the crude powder. That proportion is between 2.5 and 4%. The influence of some process parameters e.g. (N/Si and H₂/N molar ratios, internal pressure) on powder properties was also investigated. The N/Si molar ratio was found to be the most important parameter for the powder composition whereas the internal pressure plays a major role on the powder morphology.     

Preparation and characterization of ultra-fine diamond powders obtained by using a d.c. arc plasma jet

Ultra-fine diamond powders were prepared from C₂H₂ and H₂ by quenching a d.c arc plasma jet on a metal disc cooled with water. The powders obtained were agglomerated with very small particles about 20 nm in diameter, with an average size of about 80 nm. Raman spectra, X-ray diffraction, and transmission electron micrographs of them showed that each particle consisted of very small diamond crystals and a small amount of amorphous carbon, and that a single crystal particle had a twin plane. The formation mechanism of the powders has been briefly discussed from the viewpoint of the supersaturation ratio based on the classical theory of homogeneous nucleation.     

隧道施工诱发地表沉降估算方法及其规律分析

地表沉降是城市复杂环境下盾构隧道施工重点关注的问题。传统机器学习方法在预测隧道施工诱发地表沉降时忽略了其内在的物理机理,存在对训练样本需求量较大的弊端。基于深度神经网络 (deep neural networks, DNN) 对Verruijt-Booker解的围岩位移因子进行修正,构建地表沉降与隧道开挖面空间位置的关联。将修正后的Verruijt-Booker解的物理方程耦合至另一并行的DNN框架中,构建数据-物理双驱动的物理信息神经网络模型 (physics-informed neural networks, PINN),从而约束神经网络在满足物理机制的空间中进行训练。算例分析的结果表明：在同等配置的条件下,提出的PINN模型的预测效果显著优于单一数据驱动的传统DNN模型,其外推泛化性能得到显著提升。工程应用的结果表明：PINN模型可以利用施工前期的实测数据,准确预测后续施工过程中开挖面在不同位置时监测断面的地表沉降值。提出的方法有助于提高盾构隧道施工过程中地表沉降控制的智慧化程度,可为工程的潜在风险及施工决策提供预警和指导。

     

Cyclic loadings and crystallization of natural rubber: An explanation of fatigue crack propagation reinforcement under a positive loading ratio

Natural rubber is known to have excellent fatigue properties. Fatigue crack propagation studies show that, under uniaxial tension loading, fatigue crack growth resistance increases with the loading ratio, even if the peak stress increases. Studies dealing with crack initiation confirm this trend. If strain induced crystallization is believed to play a major role in this reinforcement process, it is not clear yet by which mechanism this reinforcement takes place. Using SEM investigation, it is shown here that the reinforcement process is associated with strong crack branching in the crack tip region. From experimental results it is shown that under particular reinforcing loading condition a cyclic strain hardening process can be observed on the natural rubber which is able to overcome classically observed softening effects. A cumulative strain induced crystallization process is proposed to explain the stress ratio effect on fatigue crack initiation and propagation properties of natural rubber.     

Cyclic voltammetric, a.c. and d.c. polarization behavior of boron-doped CVD diamond

Boron-doped polycrystalline diamond films have been deposited over a molybdenum substrate by the microwave plasma CVD process using a methane and hydrogen gas mixture at a pressure of 35.7 Torr. Boron doping of diamond has been achieved in situ by using a solid boron source while growing diamond in the CVD process. The a.c. impedance of boron-doped diamond films in 0.5 M NaCl solution has been determined and compared with the results obtained with a molybdenum substrate. Capacitance, solution resistance, and polarization resistance (corrosion rate) have been determined using the experimental data plotted in Nyquist and Bode formats. D.C. polarization techniques such as linear and Tafel polarization have been used to evaluate the doped diamond coated molybdenum and molybdenum for corrosion resistance characteristics in terms of charge-transfer coefficients and corrosion rate. Cyclic voltammetry has been used to evaluate the molybdenum, platinum, and doped and undoped diamond coated molybdenum materials in 0.5 M NaCl solution. We have observed two time constants with a doped diamond electrode / solution interface. Solution resistance was found to be constant irrespective of the electrode in the same electrolyte solution.     

基于开裂能密度及裂纹扩展特性的橡胶隔振器疲劳特性预测

基于开裂能密度的连续介质力学参数及橡胶材料裂纹扩展特性(裂纹扩展速率与撕裂能之关系),获得橡胶部件多轴疲劳特性计算公式,并计算某汽车动力总成橡胶隔振器的疲劳特性。计算与试验对比表明,橡胶隔振器疲劳特性预测(寿命、开裂位置及开裂方向)与实测较一致。预测疲劳寿命分布在实测疲劳寿命的1/2倍分散因子内,满足工程疲劳寿命预测要求。提出的橡胶隔振器多轴疲劳特性预测方法,可用试验效率较高、投入较少的材料裂纹扩展试验代替耗时较多的材料疲劳破坏试验,不仅能为橡胶部件前期疲劳设计提供参考,亦能大幅缩短产品疲劳设计周期。     

Adequacy equivalent development of composite generation and transmission systems using a d.c. load flow

This paper presents a technique for the development of adequacy equivalents for composite generation and transmission systems using a d.c. load flow approach. Adequacy equivalent concepts can be very useful in large composite power system adequacy evaluation where extremely long computation times are usually required. The computation time burden can be effectively alleviated by using a reduced equivalent model to represent the unchanging portion of a composite system. These reduced models, designated as reliability or adequacy equivalents, retain the essential elements in their desired form but eliminate much of the system detail. Network flow methods are usually used to develop adequacy equivalents for composite systems. The d.c. load flow technique, however, is a more widely accepted procedure for composite system analyses as it can provide more accurate solutions than a network flow method. The concepts associated with developing adequacy equivalents using a d.c. load flow method are illustrated using simple power networks. Results and analyses of system studies based on two test systems are presented in the paper.     

The detection and measurement of symmetric corner cracks by the a.c. field method

An unfolding method, developed earlier for cracks in plane surfaces, is extended in this work to provide an approximate mathematical model for the perturbations produced by a symmetrical corner crack when interrogated by a surface electric field. The model disregards the nonuniform nature of the current distribution upstream of the crack which is produced by the presence of the corner, and this simplification leads to unfolded field problems of plane Laplacian form. The Schwarz-Christoffel transformation is applied here in their solution. Experimental measurements on slots cut on steel blocks to simulate corner cracks are found to be in good agreement with the predictions of the model.     

Comparison of the characteristics of a plasma generated by a d.c. arc plasmatron and a high-voltage a.c. plasmatron with rail-shaped electrodes (gliding arc) as applied to the synthesis of carbon nanomaterials

Comparative results of investigating the parameters of plasmas generated by atmospheric-pressure electric-arc plasmatrons of two types operating in the regime of simultaneous partial oxidation of hydrocarbons and their pyrolysis, have been given. It has been established by spectral and thermophysical measurements that the component composition of the plasma and its thermal characteristics at exit from a d.c. plasmatron significantly differ from the parameters of a plasmatron of the second type — an a.c. plasmatron with rail-shaped electrodes of the gliding-arc type. The temperature nonequilibrium and the presence of the carbon dimers C₂ in the plasma (in the absence of the monomer C) generated by the rail-shaped-electrode plasmatron point to the fact that realization of the synthesis of fullerene-containing particles and, probably, particles containing nanotubes is, in principle, possible in reactors based on it, just as in more energy-intensive reactors with low-voltage d.c. arc plasmatrons. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 4, pp. 3–11, July–August, 2006.