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外加电场作用下碳纤维增强水泥基材料的输运特性 总被引:3,自引:1,他引:2
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. 相似文献
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重复升温过程中碳纤维水泥基材料的温阻特性 总被引:1,自引:1,他引:0
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. 相似文献
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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. 相似文献
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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. 相似文献
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Thermal degradation of epoxy resin/carbon fiber composites: Influence of carbon fiber fraction on the fire reaction properties and on the gaseous species release
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Duy Quang Dao Thomas Rogaume Jocelyn Luche Frank Richard Lucas Bustamante Valencia Sindonie Ruban 《火与材料》2016,40(1):27-47
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. 相似文献
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碳纤维水泥基材料吸波性能与隐身效能分析 总被引:1,自引:0,他引:1
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%. 相似文献
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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。 相似文献
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Ning Pan 《Polymer Composites》1993,14(2):85-93
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. 相似文献
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Purnendu B. Jana S. Chaudhuri A. K. Pal S. K. De 《Polymer Engineering and Science》1992,32(6):448-456
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. 相似文献
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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 总被引:1,自引:0,他引:1
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。 相似文献
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