炭黑/聚丙烯-聚(苯乙烯-乙烯/丁烯-苯乙烯)复合材料的介电性能和压阻性能

为了制备柔性较好的聚合物基压阻材料,利用熔融共混法制备了炭黑/聚丙烯-聚(苯乙烯-乙烯/丁烯-苯乙烯)(CB/PP-SEBS)复合材料,并研究了CB含量对CB/PP-SEBS复合材料介电性能和压阻性能的影响。结果表明:随着CB含量的增加,CB/PP-SEBS复合材料的介电常数、介电损耗及电导率均提高;CB/PP-SEBS复合材料发生导电逾渗时,CB的含量为12.2wt%;在CB/PP-SEBS复合材料发生弹性形变时,由于外力破坏了CB的导电网络,复合材料的电阻随着应变的增大而增大;循环压阻测试结果显示,在弹性变形区CB/PP-SEBS复合材料的电阻随着应变呈现周期性变化。研究结果可为制备具有稳定电阻变化的聚合物基压阻材料提供借鉴。     

Effect of compressive strain on electrical resistivity of carbon black-filled cement-based composites

This paper investigates the strain sensing properties of carbon black (CB)-filled cement-based composites which were prepared with 120 nm CB. A linear relationship between the fractional change in resistivity and compressive strain was observed for cement-based composites containing a large amount of CB, suggesting that this kind of composite was a promising candidate for strain sensors used in concrete structures. Tunneling effect theory and percolation theory are employed to interpret the conductivity and electromechanical properties of CB-filled cement-based composites.     

烯丙基离子液体修饰炭黑/硅橡胶复合材料的压阻特性

为改善炭黑在硅橡胶中的界面性质,通过机械研磨法,采用1-烯丙基-3-甲基-咪唑氯盐对炭黑进行表面修饰,再与硅橡胶混炼制备炭黑填充硅橡胶柔性复合压阻材料,研究了修饰炭黑对复合材料的导电渗流和压阻行为、压阻松弛和循环特性的影响。扫描电镜表明,与未经修饰的炭黑对比,修饰炭黑在硅橡胶基体中形成炭黑离子凝胶结构。由于炭黑离子凝胶的增塑作用及在靠近时相互排斥和在远离时相互吸引作用,离子液体修饰炭黑/硅橡胶复合材料较炭黑/硅橡胶具有更敏感的正压阻效应和更短的压阻松弛时间,并且循环压缩测试结果表明离子液体修饰炭黑/硅橡胶复合材料电阻变化具有更好的可重复性。     

I–V characteristics and electro-mechanical response of different carbon black/epoxy composites

I–V characteristics and electro-mechanical response of carbon black (CB)/epoxy composites were studied experimentally. Two types of CB were used in the experiment, they were: sprayed CB and conductive CB particles. During the experiment, it was found that the I–V characteristics of the composites and their electro-mechanical response were greatly affected by the particle size of CB as well as their dispersion properties. The epoxy containing sprayed CB with the diameter of 123 nm composites gave predicted relationships, in terms of I–V characteristics and strain/electrical resistivity once they were subjected to a compressive load. The electrical breakdown assumption incorporated in the DC circuit model is proposed in this paper to interpret the response of the composites with different types of CB particles.     

Development of moulded pulp materials for the packaging of electronic equipment

A new shredded pulp–plastic microsphere composite with modified starch binder which is applicable to the packaging of electronic equipment has been developed. This composite with a 3 wt% microsphere content has almost the same compressive stress at 50% compressive strain as that of (poly)styrene foam, which has a specific gravity of 0.025. A moulded sample of the above composites can be released from a mould after 1.5 minutes of steam heating, the same cycle time as that of styrene foam. © 1997 John Wiley & Sons, Ltd.     

Dynamic response for porous epoxy resin matrix composites filled with iron powder at different strain rates and constitutive relationships

The porous epoxy resin matrix composites filled with iron powder referenced in this work consist of both ferromagnetic base materials and porous materials, which have properties of electromagnetic shielding and impact energy absorbing. Aimed at the dynamic compressive properties of the composites at different high strain rates, two materials were studied: the first is Fe/ER-17 with 40% porosity and 17% mass fraction of iron powder; the other is Fe/ER-90 with 10% porosity and 90% mass fraction of iron powder. The investigation results showed: (1) the quasi-static compressive failure strengths of the two composites are much lower than their dynamic compressive failure strengths; (2) Fe/ER-17 exhibits obvious characteristics of a porous material at high strain rates (≥3000/s), whereas FE/ER-90 exhibits a visco-elastic response at all strain rates; (3) Fe/ER-17 and Fe/ER-90 show a strain rate hardening effect on dynamic yield strengths. The dynamic yield strengths of Fe/ER-17 change from 19.23 MPa at a strain rate of 850/s to 30.97 MPa at a strain rate of 6000/s, and dynamic yield strengths of Fe/ER-90 change from 114.93 MPa at a strain rate of 700/s to 136.95 MPa at a strain rate of 3600/s. The hardening effect of dynamic yield strengths is linear with the strain rate, and their linear strain rate hardening factors are very small (10 × 10^?4 and 0.6 × 10^?4, respectively). A constitutive model of series form for a porous material and a modified ZWT constitutive model for a visco-elastic material were adopted for Fe/ER-17 and Fe/ER-90, respectively. The constitutive relationships developed captured the dynamic compressive characteristics of the two materials.     

The influence of adding pitch to resin as a matrix precursor on properties of carbon-carbon composites

Carbon-carbon composites were prepared with commercially available carbonized and graphitized fibres, with a mixture of pitch and phenolic resin as a binder and pitch as an impregnant. The contents of pitch in mixtures were: 0, 10, 20 and 30 wt %. The influence of pitch content in the mixture and fibre type on mass loss, shrinkage and mechanical properties of the composites was examined. With an increase of pitch content mass loss and shrinkage increased, while mechanical properties decreased. After three densification cycles, flexural strength increased with increasing pitch content in the binder, especially for composites with graphitized fibres.     

Prediction of compressive strength and optimization of mixture proportioning in ternary cementitious systems

This paper discussed the application of the method of the simplex-lattice design for predicting the properties of cement-based composites. On the basis of the compressive strength, its use was demonstrated on ternary paste systems composed of cement, silica fume and fly ash with constant water to binder ratio and a mass fraction of mineral admixtures not exceeding 30%. The regression model between compressive strength of paste and binder proportion was built up. The F-test method was utilized for validation of the regression model. The nonlinear programming system with upper and lower bound was solved. This allowed assessment of optimum mixture proportions and corresponding maximum compressive strength. It was shown that: (1) the 3rd-order regression model constructed by using the simplex-lattice design method could accurately predict the compressive strength in ternary paste system made of cement, silica fume and fly ash (the total mass fraction of all mineral admixtures was up to 30%); (2) to solve the nonlinear programming with the constraints of upper and lower bound played an important role in getting the optimum compressive strength and its corresponding mixture proportion at different ages; (3) the combination of the simplex-lattice design method and the optimization theory could be valuable tool for optimization of cement-based composites' properties.     

Effect of coal tar pitch modified by sulfur as a binder on the mechanical and tribological properties of bronze-impregnated carbon-matrix composites

Bronze-impregnated carbon-matrix composites were prepared through compression molding, carbonization and impregnation. The mechanism of sulfuration was studied, and the effect of coal tar pitch modified by sulfur as a binder on the mechanical and tribological properties of composites was investigated by varying the content of sulfur. The results showed that the sulfur addition increased the softening point, carbon yield and C/H atomic ratio of coal tar pitch but decreased the toluene solubility and quinoline solubility due to the dehydrogenating polymerization of pitch molecules. The micro-hardness, bending strength and compressive strength of the composites were enhanced by increasing the mass percentage of sulfur and reached a maximum of 160 HV, 132.82 MPa and 293 MPa at 7 wt. % of sulfur, respectively. However, both the hardness and strength of the composites decreased as the content of sulfur increased beyond 7 wt. %. The friction coefficient value of composites increased monotonously, but the wear rate decreased with increasing sulfur content; subsequently, the wear rate reached a minimum of 3.045 × 10⁻⁷ mm³/Nm at 7 wt. % of sulfur and then ascended. The wear mechanisms of the composites were adhesive wear, abrasive wear and oxidative wear. However, adhesive wear and oxidative wear occurred slightly for the composites with the binder modified by sulfur.     

聚乙烯醇纤维增强钢渣粉-水泥复合材料基本力学性能及微观结构

通过掺加钢渣粉来制备聚乙烯醇（PVA）纤维增强钢渣粉-水泥基复合材料,从宏微观两个方面研究了这种复合材料的性能。考虑了基体材料的水胶比（0.25和0.35）、不同钢渣粉质量分数（0、30wt%、60wt%、80wt%）,采用抗压强度试验、薄板四点弯曲试验研究了PVA纤维增强钢渣粉-水泥基复合材料的基本力学性能变化规律及其在弯曲荷载作用下的裂缝控制能力,采用扫描电镜观测了破坏后试样的微观结构。结果表明,水胶比和钢渣粉掺量均可明显影响PVA纤维增强钢渣粉-水泥基复合材料的基本力学性能,在低水胶比条件下（水胶比为0.25）,钢渣粉掺量达到80wt%时,试样表现出较高的韧性指数和良好的裂缝控制能力,基本满足工程所需强度要求,水胶比为0.35时钢渣掺量不宜超过60wt%;同时,从节能减排的角度考虑,利用钢渣粉制备PVA纤维增强钢渣粉-水泥基复合材料是可行的。      

Multi-walled carbon nanotubes/silicone conductive foams and their piezoresistive behaviors

Multi-walled carbon nanotubes/silicone conductive nanocomposites are of great significance because of their unique electrical and mechanical properties and are expected to open up a new field of applications as smart functional materials. Especially their noticeable piezoresistive behaviors can be utilized to produce flexible tactile sensors with large sizes but low costs. To enhance the sensitivity of the piezoresistive property, a foaming procedure was introduced to the conductive polymeric composites. A series of novel multi-walled carbon nanotubes/silicone conductive foamed nanocomposites were fabricated with different types of foaming agents to obtain a diverse porous structure. The porous structures of the foams, the distribution and orientation state of the multi-walled carbon nanotubes in the silicone matrix were both observed using a laser microscope and SEM with or without a compressive load. The influences of the porous structure and porosity on the foam were studied. It was found that a different porosity and different voids structure affected the density, elastic modulus, resistivity as well as piezoresistive property significantly. A piezoresistive model for the conductive fillers reinforced elastomeric composites was developed, the calculated results of resistive variations were used to compare to the measured values. Although the overall trends of the resistance changes matched, notable separations were found between the theoretical values and the measured values, which are thought to be caused by the viscoelasticity of the silicone matrix.     

混凝土柱单轴动态抗压特性的应变率效应研究

混凝土材料是典型的率敏感材料,不同动态应变率下混凝土柱的抗压性能有明显的变化。本文通过混凝土柱的轴心动态抗压试验,在10-5/s10-2/s应变率范围内研究了混凝土材料本构关系的应变率效应,系统研究了应变率效应对混凝土抗压强度、弹性模量、峰值应变、吸能能力以及破坏机理的影响,并讨论了试验机刚度、惯性效应对试验结果的影响。试验结果表明：随着应变率的增加,混凝土材料的抗压强度也随之增加,当应变率为10-4/s、10-3/s、10-2/s时混凝土的抗压强度相对准静态抗压强度（应变率为10-5/s）分别增加了7.45%、19.51%和29.23%,弹性模量相对于准静态弹性模量变化不大,峰值应变具有一定的离散性,但是基本趋势也是增加的,混凝土的吸能能力也随着应变率的增加而显著增加。另外,刚性元件的使用有效的改善了试件应变率的稳定性,惯性效应对本次试验结果的影响可以忽略     

基于炭黑填充导电橡胶的力敏传感器的灵敏度

以通用有效介质理论为基础, 给出了炭黑填充导电橡胶(炭黑/橡胶)的力敏传感器灵敏度计算方程。采用该方程并结合形变和压阻效应, 分析了影响力敏导电炭黑/橡胶的灵敏度的主要参数。结果表明: 炭黑体积分数是影响力敏导电炭黑/橡胶的灵敏度的主要参数。当炭黑体积分数在临界体积分数附近时, 力敏导电炭黑/橡胶的灵敏度为0.1～11.5 MPa^-1, 其敏感机制主要为压阻效应。当炭黑体积分数在渗流区时, 灵敏度为0.2～3.6 MPa^-1, 其敏感机制还与接触压力的大小有关, 压力较小时, 主要为压阻效应; 压力较大时, 主要为应变效应。若炭黑体积分数在传导区, 灵敏度为0.3～1.7 MPa^-1, 其敏感机制主要为应变效应。     

CB/PBO复合材料制备及吸波性能研究

以4, 6二氨基间苯二酚盐酸盐(DAR?2HCl)、对苯二甲酸(TPA)为原料, 合成TA盐, 再缩聚制得具有较高耐热性的聚对苯撑苯并二噁唑(PBO)。以PBO为基体, 炭黑(CB)为吸收剂, 热压法制备CB/PBO复合材料。对不同炭黑质量分数的复合材料介电及PBO基体与复合材料的热性能进行研究。结果表明, 随着炭黑含量的增加, 材料的复介电常数的实部与虚部均增大。含5%炭黑的试样厚度达到2 mm时, 吸波性能最好, 反射率小于-10 dB的带宽可达2.4 GHz, 最小反射率可达-32 dB。在空气中450℃保温5 h, PBO的质量损失为11.84%, 而5% CB/PBO复合材料的质量损失为21.99%。     

熔融酯交换法原位合成炭黑/聚碳酸酯导电复合材料

利用原位聚合法合成具有导电性能的炭黑(CB)/聚碳酸酯(PC)复合材料。在聚合反应过程中, CB与PC在较低黏度下更好地混融, 而且通过负载催化剂连接CB和PC分子, 使CB参与PC链增长过程, 从而使CB有效分散。与传统的熔融共混法相比, 利用原位聚合法制备的CB/PC导电复合材料的渗滤阈值低, 当复合材料的体积电阻率为1.56×10⁶ Ω·mm时, CB的质量分数仅为4.32%。通过SEM观察发现, 原位法得到的样品中CB与PC充分混融, 形成导电网络更充分有效。利用原位聚合法得到的样品的正温度系数(PTC)的对数值达到4.69, 具有作为自控温材料的潜力。     

Simultaneous global and local strain sensing in SWCNT-epoxy composites by Raman and impedance spectroscopy

Polymer composites can be benefited in many ways through the addition of carbon nanotubes (CNT). For instance, CNT can build up a percolated network within the polymer matrix, which results in a composite material with electrical conductivity and piezoresistive characteristics. This has very important implications for the realization of self-stress sensing structural composites. Moreover, the remarkable optical and transport properties of CNT permit to obtain information about the stress state of the composite at different scales. In the present work, the local and global stress response of SWCNT-epoxy composites is characterised by simultaneous Raman spectroscopic and electrical measurements on nanocomposite specimens submitted to different levels of surface strain. Both the Raman G′-band resonance frequency and the electrical resistance of the composite are found to change monotonically with strain until an inflection point is reached at ∼1.5% strain. Increased sensitivity of the piezoresistive network and lower load transfer efficiency occur beyond this strain level, and are considered to be the result of CNT slippage from the polymer. The reversibility of the stress sensitivity of the composites is verified by performing cyclic loading tests. Hysteresis loop are found to develop earlier on the Raman curves as in the resistance curves, which indicates that even at low strain levels, permanent damage is induced in the vicinity of carbon nanotubes. The use of Raman spectroscopy in combination with electrical methods provides a further insight on the stress sensing capabilities of CNT and the factors which affect the sensitivity and reproducibility of this behaviour.     

Dynamic properties of pultruded natural fibre reinforced composites using Split Hopkinson Pressure Bar technique

The paper presents results on dynamic mechanical properties of jute, and kenaf fibre reinforced composites at various strain rates using compression Split Hopkinson Pressure Bar technique. The stress–strain curves for both pultruded natural fibre reinforced composites at strain rates of nearly 1400 s⁻¹ are illustrated and then compared with statically determines stress–strain curve (1.0 × 10⁻³ s⁻¹). Results show that the strain rate does affect the value of dynamic compressive properties of both pultruded natural fibre composites. Higher dynamic compression modulus and 2.5% flow stress were recorded for higher strain rates as compared to lower strain rate over the range of strain rates investigated. Under dynamic loading, jute fibre reinforced composites recorded the highest value of dynamic response in terms of compression modulus, 2.5% flow stress and compressive strength than that of kenaf fibre reinforced composites. In addition, kenaf fibre reinforced composites is more severely damaged as compared to jute fibre reinforced composites for all tested strain rate.     

石墨烯铝基复合材料的制备及性能分析

采用真空热压烧结工艺制备了石墨烯质量分数分别为0.1%、0.5%和1.0%的添加粘结剂与不加粘结剂的两种6061铝复合材料,对其致密度、硬度和导电性进行了测试分析。结果发现,添加粘结剂的复合材料在石墨烯质量分数为0.1%时就开始出现Al4C3,而不添加粘结剂的复合材料在石墨烯质量分数为0.5%时才开始出现Al4C3,其原因是添加粘结剂的复合材料中的石墨烯先与纳米铝粉混合,使石墨烯更容易与铝发生反应。随着石墨烯质量分数的增加,两种复合材料的致密度和导电性降低,硬度增加。其原因都是随着石墨烯质量分数的增加Al4C3增加,且石墨烯团聚现象也越严重。粘结剂的添加对复合材料的致密度、导电性以及硬度都有较大的影响。     

Ti-C含量对多孔TiC/FeAl复合材料孔型结构和力学性能的影响

以尿素为造孔剂,利用自蔓延高温合成技术制备了多孔TiC/FeAl复合材料,主要考察了Ti-C含量（质量分数为15wt%~35wt%）对多孔TiC/FeAl复合材料孔型结构和压缩性能的影响。当Ti-C含量不高于25wt%时,多孔TiC/FeAl复合材料由毫米孔和孔壁微孔组成规则的复合孔型结构。相互连通的毫米孔产生于尿素颗粒的挥发和液相迁移;微孔尺寸为10~50 μm,产生于Fe-Al-Ti-C粉末的自蔓延过程,孔径随Ti-C含量的增加而增大。通过调整尿素的体积分数,多孔TiC/FeAl复合材料的孔隙率可控制在56.64%~85.35%。当Ti-C含量不高于25wt%时,多孔TiC/FeAl复合材料的抗压强度随Ti-C含量的增加而增大。当Ti-C含量高于25wt%时,多孔TiC/FeAl复合材料壁面微孔形状很不规则,且抗压强度下降。孔隙率约为64.3%时,多孔Fe-Al金属间化合物和TiC/FeAl复合材料（Ti-C含量为25wt%）的抗压强度分别为20.03 MPa和66.68 MPa,对应的应变值分别为4.77%和8.21%。另外,多孔TiC/FeAl复合材料的压缩性能可用Gibson-Ashby模型来解释。     

凹凸棒粘土对炭黑/环氧复合材料电性能的影响

通过溶液混合法制备了凹凸棒(ATT)/炭黑(CB)/环氧树脂(EP)复合材料。使用紫外可见光光谱仪(UV-Vis)和Zeta电位测试仪对CB和(或)ATT在丙酮溶剂中的分散稳定性进行了研究。使用扫描电子显微镜(SEM)和电阻仪分别研究了不同填料比例以及含量对EP复合材料微观结构和电阻率的影响。结果表明,ATT的加入可以有效增强CB在溶剂中的分散稳定性并促进EP基体中导电网络的形成。当CB与ATT质量比为5∶1时,复合材料的电阻率比不添加ATT时下降了2个数量级;其渗流阈值(1%)(质量分数,下同)小于具有相同填料含量的CB/EP复合材料(1.8%)。最后探讨了ATT对CB/EP复合材料电性能影响的可能机理。