外加电场作用下碳纤维增强水泥基材料的输运特性

以隧道效应理论为基础,建立了碳纤维增强水泥基复合材料(carbon fiber reinforced cement-based composites,CFRC)导电模型.研究CFRC材料在外加电场作用下的输运特性,得出了相应的数学表达式,并进行了实验验证.结果表明:CFRC材料的电阻率-场强曲线呈反S形;随碳纤维掺量的增加,场强对其电阻率的影响逐渐减小.CFRC材料具有这种特殊的输运特性,是由于隧道导电存在的结果.     

重复升温过程中碳纤维水泥基材料的温阻特性

碳纤维水泥基材料(carbon fiber reinforced cement-based composites,CFRC)经过重复升温后,不同碳纤维掺量的CFRC材料的温阻特性各异.低于渗流阈值(碳纤维掺量分别为0.1%和0.2%,质量分数,下同)的低掺量CFRC材料,在20～130℃范围内第1次升温过程中,碳纤维掺量为0.1?RC材料电阻率随温度升高而降低;碳纤维掺量为0.2%的CFRC材料呈弥散性波动,然而在随后的重复升温过程中,在同样的温度范围内,其电阻率均随温度升高而增大.而碳纤维掺量高于渗流阈值(碳纤维掺量分别为0.3%和1.0%)的CFRC材料在同样的温度范围内,第1次升温和随后的重复升温过程中,其电阻率随温度的升高而单调减小.不同碳纤维掺量的CFRC材料在经历第1次升温后,其常温(20℃)时的电阻率均有不同程度地减小,减小的幅度随碳纤维掺量增加而降低.     

超高性能混凝土的拉伸敏感性实验研究

研究了超高性能混凝土(UHPC)的拉伸力学性能、导电性和拉伸时的电阻变化.研究表明,随着钢纤维掺量的增加,UHPC的拉伸强度和导电性能提高.在拉伸过程中,UHPC的电阻随拉伸应变的增加先降低后缓慢上升.在峰值荷载前,UHPC对拉应变的敏感性随钢纤维掺量从1％增至2％而提高.UHPC在达到峰值拉应力前电阻降低,这是由于裂纹区靠钢纤维导电,并引起非裂纹区域导电通路缩短所致.     

导电橡胶及其应用

介绍橡胶的导电机理、影响橡胶导电性能的因素以及导电橡胶的分类和应用.橡胶的导电机理主要有宏观渗流理论即导电通路机理、微观量子力学隧道效应和微观量子力学场致发射效应.导电填料品种和用量决定了橡胶的导电性能,配方其它因素对橡胶导电性能也有影响.导电橡胶主要用于防过电流/过热元件、开关、传感器、导电橡胶条、导电橡胶板和防静电鞋底等.     

碳系导电填料的导电橡胶研究进展

阐述导电橡胶的导电机理(主要为导电通路、隧道效应和电场发射理论),介绍炭黑、碳纤维、碳纳米管、石墨和石墨烯等碳系导电填料在导电橡胶中的应用研究进展。各类碳系导电填料单用或并用的导电橡胶可用于制备抗静电材料、电磁屏蔽材料、吸波材料、高压电缆、光电子器件和分子导线等。     

导电橡胶及其应用

介绍了导电橡胶的导电机理和应用。导电机理主要有宏观渗滤理论即导电通路机理和量子力学隧道效应理论；导电橡胶主要有等向性导电橡胶、异向性导电橡胶、压敏导电橡胶、电磁屏蔽用导电橡胶和抗静电导电橡胶等。     

碳纤维对导电混凝土性能和微结构的影响

导电混凝土较好的导电性能,可用于道路工程除冰,保障交通通行安全.采用碳纤维制备导电混凝土,观察其性能和微结构的变化.研究结果表明:碳纤维的掺用使得混凝土拌合物的工作性变差,但仍然能满足施工要求.随着碳纤维掺量的增加,导电混凝土的抗压强度下降,但劈拉强度增大.导电混凝土的电阻率随碳纤维掺量的增大而降低,持续通电后,呈良好的电热效应和发热效果.掺加碳纤维后,水泥石结构的密实性降低,从而导致其性能发生变化.     

聚合物基导电复合材料几种导电理论的评述

近年来,有关聚合物基导电复合材料的研究已受到普遍的重视,但对导电复合材料导电机理研究的不足制约了其应用和发展。导电复合材料的导电机理相当复杂,通常可分为导电通路如何形成和材料形成导电通路后如何导电这两个方面来研究。人们提出了许多导电机理模型,详细介绍了渗滤理论、有效介质理论、量子力学隧道效应理论等几种具有代表性的导电理论,对其适用范围、优缺点等进行了评述。通过对这些导电机理的探讨,有助于加深对复合型导电塑料以及其它导电复合材料导电行为的了解。     

炭纤维增强水泥基复合材料的导电性研究

通过向水泥基材料中添加炭纤维制备炭纤维增强水泥基复合材料(CFRC),研究了炭纤维掺量、硅粉掺量、养护龄期等因素对其导电性能的影响。结果表明,CFRC复合材料的电阻率随着炭纤维掺量的增加而减小;掺入10%的硅粉能够显著降低CFRC复合材料的电阻率;CFRC复合材料中的炭纤维掺量低于0.6%时,电阻率随着养护龄期的延长而迅速增大,炭纤维掺量高于0.6%时电阻率增加不明显。     

导电复合橡胶研究进展

介绍了导电复合橡胶的两大导电机理,即导电通路学说和量子力学隧道效应学说;对炭系、金属系、颗粒表面镀金属、本征导电聚合物填充制备导电复合橡胶的研究进展状况进行了综述;并从聚合物并用、温度、压力等方面对复合型导电橡胶导电性能的影响因素进行了综述。     

Double percolation in the electrical conduction in carbon fiber reinforced cement-based materials

Electrically conductive cement-based materials are important as multifunctional structural materials. Double percolation has been observed for the first time in the electrical conduction in carbon fiber cement-based materials. It involves fiber percolation and cement paste percolation. The fiber percolation threshold increases with increasing sand/cement ratio and ranges from 0.30 to 0.80 vol.% fibers in the paste portion. The cement paste percolation threshold is between 70 and 76 vol.% carbon fiber cement paste in the mortar. A sand volume fraction of 24% or less (i.e., a sand/cement ratio of 0.75 or less) and a fiber content of 0.80 vol.% (or more) of the paste portion are recommended for attaining high conductivity. The use of a higher sand/cement ratio requires a higher fiber content to attain the same level of conductivity. For a compromise between cost and conductivity, a sand/cement ratio of 0.75 and a fiber content of 0.80 vol.% of the paste portion (corresponding to 0.59 vol.% of the mortar) is attractive. At a fixed fiber volume fraction in the paste portion, the conductivity of the mortar decreases with increasing sand/cement ratio.     

The role of electronic and ionic conduction in the electrical conductivity of carbon fiber reinforced cement

Electrical conduction in carbon fiber reinforced cement with a fiber volume fraction below the percolation threshold involves electrons and ions. The fiber affects both the electronic conduction and the ionic conduction. The ozone treatment of the fiber surface helps the ionic conduction. Latex as an admixture helps provide a relatively high ionic conductivity; silica fume as an admixture helps provide a relatively high electronic conductivity. In the dry state (the state of practical importance attained by room temperature drying), electronic conduction is more significant than ionic conduction. In the wet state (water saturated state), ionic conduction dominates. When silica fume is present with the fiber, the fractional electronic contribution in the dry state is 0.99. When latex is present with the fiber, the corresponding value is 0.72-0.78. The ratio of the wet ionic conductivity to the dry ionic conductivity is much increased by fiber surface treatment and is higher when latex rather than silica fume is used. The wet ionic conductivity is much higher than the dry overall conductivity when latex is present, but is lower than or comparable to the dry overall conductivity when silica fume is present; the wet ionic conductivity is lower than the dry overall conductivity when the fiber is not treated and silica fume is present.     

Thermal degradation of epoxy resin/carbon fiber composites: Influence of carbon fiber fraction on the fire reaction properties and on the gaseous species release

The thermal degradation of epoxy resin/carbon fiber composites has been performed in ISO 5660 standard cone calorimeter using a piloted ignition. Two kinds of composites that differ by their volume fractions in carbon fiber (56 and 59 vol.%) were tested in this study. The cone calorimeter irradiance level was increased up to 75 kW m^?2 to characterize the carbon fiber volume fraction influence on the composite thermal degradation. Thus, main flammability and combustibility parameters were determined and calculated such as mass loss, mass loss rate, ignition time, thermal response parameter, ignition temperature, thermal inertia, and heat of gasification. As a result, all the characteristic parameters for the thermal resistance of composites were decreased when the carbon fiber volume fraction increased. Moreover, the main gaseous products (such as NO, CO, CO₂, HCN, H₂O, and lightweight hydrocarbons) emitted as well as the oxygen consumption during the composite thermal decomposition were also quantified simultaneously with a portable gas analyzer and a Fourier transform infrared spectrometer. The main species emission yields calculated from the gas analysis results increased slightly when the carbon fiber volume fraction was increased in the initial sample. The epoxy composite was represented as a sooty material with a significant production of soot particles during the combustion process. Furthermore, heat release rate, total heat release, and effective heat of combustion were calculated by using the oxygen consumption calorimetry technique. The results obtained showed that a small increasing of composite carbon fiber amount induced a sharp decrease of heat release rate and total heat release. Copyright © 2014 John Wiley & Sons, Ltd.     

碳纤维水泥基材料吸波性能与隐身效能分析

采用远场雷达散射截面法测试的功率反射率为表征吸波性能的指标,研究了素砂浆的吸波性能以及碳纤维长度、碳纤维掺量、搅拌方法、复掺铁氧体、温度和湿度等因素对碳纤维砂浆吸波性能的影响,根据所推导的隐身效能评价公式计算了碳纤维砂浆的隐身能力.研究表明:掺入碳纤维只能提高砂浆的高频吸波性能;合适的纤维长度和体积掺量是提高砂浆吸波性能的决定性因素;机器搅拌方法制备的碳纤维砂浆的吸波性能好于人工搅拌方法制备的碳纤维砂浆;温度、湿度升高,或者复掺铁氧体、碳纤维砂浆的吸波性能均下降;最佳配比的碳纤维砂浆在14～18GHz的频段内,其雷达最大探测距离可降低到素砂浆的80%～90%.     

炭纤维/树脂复合材料导热性能的数值模拟

采用有限元方法对炭纤维/树脂复合材料的导热性能进行了数值模拟,分别建立一维结构和二维结构炭纤维/树脂复合材料计算分析模型,研究炭纤维含量、界面接触热阻、以及炭纤维直径对复合材料有效热导率的影响。研究结果表明炭纤维作为复合材料增强相,其含量越高复合材料的热导率越高;界面的接触热阻在10-3~10-5(m2 K)/W范围内对复合材料有效热导率有较大的影响,超出范围之后改变接触热阻对材料热导率的影响可以忽略;接触热阻比较大时,炭纤维的直径对复合材料的热导率有较大的的影响,当接触热阻比较小时,炭纤维的直径对于复合材料热导率的影响非常小。     

Theoretical determination of the optimal fiber volume fraction and fiber-matrix property compatibility of short fiber composites

Although the question of minimum or critical fiber volume fraction, beyond which a composite can then be strengthened due to addition of fibers, has already been dealt with by several investigators for both continuous and short fiber composites, a study of maximum or optimal fiber volume fraction at which the composite reaches its highest strength has not been reported. The present analysis has investigated this issue for short fiber case based on the well-known shear lag (the elastic stress transfer) theory. Using the relationships obtained, the minimum spacing between fibers is determined upon which the maximum fiber volume fraction can be calculated. The effects on the value of this maximum fiber volume fraction due to such factors as the mechanical properties of the fiber and matrix, the fiber aspect ratio, and fiber packing forms are discussed. Furthermore. Combined with the previous analysis on the minimum fiber volume fraction, this maximum fiber volume fraction is used to examine the property compatibility of fiber and matrix in forming a composite. This is deemed to be useful for composite design. Some examples are provided as well to illustrate the results.     

Electrical conductivity of short carbon fiber-reinforced polychloroprene rubber and mechanism of conduction

The effects of concentration and aspect ratio of carbon fiber and temperature on volume resistivity of polychloroprene-carbon fiber composites have been studied. The critical concentration of fiber wherein a sharp transition of electrical performance occurs from insulative range to conductive range is in the range of 5 to 10 phr for fibers of higher aspect ratio (～ 100) and in the range of 20 to 25 phr for fibers with lower aspect ratio (～ 25). Experimental values of electrical conductivity agreed reasonably well with the calculated values from a theory based on probability of formation of conductive network. Heating and cooling curves in the variation of volume resistivity with temperature do not follow the same path and results in a “hysteresis loop,” up to carbon fiber loadings of 30 phr. Such loops disappear at 40 phr loading. The activation energy of conduction for carbon fiber-filled polychloroprene varies from 1.10 × 10^?20 to 0.96 × 10^?20 J. Linearity in current-voltage relation was observed at room temperature. Increasing interfiber distance at higher temperatures disrupts the linear relation. The type of carrier in carbon fiber-filled polychloroprene thermovulcanizate was found to be n-type. The carrier concentration and drift mobility determined by studying the Hall effect were found in the range of 2.5 × 10²² to 2.90 × 10²⁵ m^?3 and 1.66 × 10^?4 to 14.25 × 10^?4 m² V^?1 s^?1, respectively.     

短纤维增强SiC／Al复合材料在高温下粘弹性拉伸性能的细观力学分析

本文采用细观力学模型和有限元法研究短纤维增强ＳｉＣ／Ａｌ复合材料在高温下的粘弹性行为，着重讨论了纤维体分比和长径比对复合材料总体蠕变性能的影响。结果表明，随着纤维体分比和长径比的增加，纤维能显著抑制复合材料沿轴向蠕变行为。     

微螺旋碳纤维/高密度聚乙烯复合材料电渗流行为及机制

以微螺旋碳纤维(CMCs)作为复合材料的导电填料,以高密度聚乙烯(HDPE)作为复合材料的基体树脂,研究了CMCs/HDPE基复合材料的电渗流行为、渗流阈值附近复合材料的导电机制。结果表明:CMCs/HDPE复合材料存在明显的渗流行为,其渗流阈值为6.28%(CMCs的体积分数)或9.77%(CMCs的质量分数);当CMCs的体积分数接近于渗流阈值时,CMCs/HDPE复合材料的导电方式由隧道效应所致。     

镀铜碳纤维布的制备及性能研究

为制备新型毫米波无源干扰材料,采用化学镀方法在碳纤维布表面沉积了金属铜层。测量了优化工艺条件下制得的镀铜碳纤维布的表面电阻,并采用冷热循环法检测了镀层的结合强度,应用雷达散射截面(RCS)测试系统测试了同样尺寸的镀铜碳纤维布及未改性碳纤维布的3mm波段RCS值。结果表明:镀铜碳纤维布镀覆均匀,金属光泽强,有良好的镀层结合强度及较强的导电性能。镀铜碳纤维布在3mm波段的RCS值较未改性碳纤维布有很大提高,且与理论计算值接近。