碳纤维增强水泥复合材料的电导性能及其应用

研究了碳纤维增强水泥复合材料的电导性能, 用扫描电子显微镜(SEM ) 观察了材料产生电导渗流时的显微结构, 讨论了纤维掺量和纤维长度对电导性能的影响以及受载过程中材料电导率的变化规律。结果表明, 适当控制碳纤维的尺寸、含量, 可以明显提高材料的电导性能; 材料结构中存在电导渗流现象, 渗流阈值随受载过程而变化; 碳纤维增强水泥复合材料能够作为本征机敏材料, 反应试件受载时的应力应变关系。     

Electrical conductivity of self-monitoring CFRC

The present work is concerned with the analysis of the electrical conductivity in carbon fiber reinforced cement composites and of the main parameters influencing the phenomenon: fiber volume fraction, fiber length, hydration time and sand–cement ratio. AC measurements were carried out on CFRC (carbon fiber reinforced cement) and the experimental results were analyzed using the percolation theory. The present study could be useful for the adoption of CFRC as a smart material.     

掺CCCW的碳纤维石墨水泥基复合材料的导电及压阻特性

利用四电极法研究了内掺水泥基渗透结晶防水材料(CCCW)的碳纤维石墨水泥基复合材料试样(40 mm×40 mm×40 mm)的导电特性及其在循环荷载作用下的压阻特性,分析讨论了碳纤维石墨水泥砂浆的体积电阻率及压阻特性随石墨掺量的变化规律。碳纤维和CCCW的掺量分别为水泥质量的1%和4%;石墨掺量分别为水泥质量的0%、10%、20%、30%、40%和50%。结果表明,添加CCCW的碳纤维石墨砂浆试样的体积电阻率随石墨掺量的增加迅速下降,并存在渗滤现象,渗滤阈值为20%左右。在循环荷载作用下,不同石墨掺量试样的电阻和应力存在一定的对应关系。石墨掺量为水泥质量的20%～30%时,碳纤维石墨水泥砂浆试样的体积电阻率与压应力呈现良好的可重复性,电阻值在应力加载时几乎呈线性下降,而卸载时增加。     

碳纤维水泥基材料的机敏特性研究

水泥基材料是一种高电阻率的惰性材料,通过掺入一定体积含量(0.2 vol%~1.2 vol%)的短切碳纤维,可显著提高其电导率。本文作者研究了碳纤维水泥基材料表观电导特性与其内部微观结构的关系,探讨了电阻率的变化与材料所受外部荷载的关联性。结果表明碳纤维水泥基材料具有实时诊断内部损伤的机敏性:当水泥基材料内部裂纹产生或扩展时,表现为材料电阻率上升;而当水泥基材料内部裂纹闭合时,其电阻率下降。碳纤维水泥基材料的电阻变化与所受荷载呈良好的线形关系;而不含碳纤维的普通水泥基材料在整个受荷过程中,其电导特性则无明显变化。碳纤维水泥基材料电导特性的变化反映了水泥基材料内部损伤状况丰富的信息,根据这一特性可以及时预报水泥基材料内部潜在的损伤状况,有效地防止灾难性的破坏。     

填充型聚合物基复合材料的导电和导热性能

研究了高密度聚乙烯为基体、炭黑和炭纤维为填料复合体系的导电和导热性能。发现当导电填料的含量达到渗流阈值时,复合材料的电导率急剧升高;而在渗流阈值附近,其热导率未出现突变。这表明电导渗流现象不完全是由导电粒子通过物理接触生成导电链所致。其导电机制是相当数量的导电粒子相互发生隧道效应。     

碳纤维水泥基材料导电性与压敏性的试验研究

首先用正交试验研究了分散剂、消泡剂和水灰比对碳纤维水泥浆扩展度和水泥石导电性的影响,而后研究了碳纤维长度对水泥石导电性的影响,最后研究了复合6mm长碳纤维水泥石的压敏性.结果表明:碳纤维水泥石配合比决定了纤维和水泥粒子的分散性,也最终决定了材料的导电性;碳纤维长度越长、掺量越大,对水泥石导电性的改善效果越好,6 mm长碳纤维的渗流临界体积率在0.278%左右,而3 mm长碳纤维的渗流临界体积率在0.54%左右;一次压载至破坏前,复合有0.18%到0.5%碳纤维的水泥石的电阻率具有17%到35%左右的线性降低趋势,且处于渗流区的变化率大于处于过渗流区的情况.     

气相生长碳纤维增强水泥基复合材料的制备及性能

研究了脱油沥青(De-oiled asphalt)基气相生长碳纤维(VGCFs)增强水泥基复合材料的制备方法及其性能。以脱油沥青作原料,采用化学气相沉积法(CVD)制备出气相生长碳纤维,以此纤维制备水泥基功能复合材料。结果表明:低含量VGCFs的碳纤维增强水泥基复合材料具有良好的抗压强度和导电性能,在VGCFs的掺量由0增至0.6 %范围内,随着VGCFs掺量的增加,碳纤维增强水泥基复合材料的电阻率下降,抗压强度提高。当VGCFs为0.4 %时,VGCFs水泥基复合材料电阻率降低2个数量级,从3.25 ×105 Ω·cm 降为1.49 ×103 Ω· cm ,抗压强度提高28.8 %,为最佳掺量。      

碳纤维含量对短碳纤维－铜复合材料性能的影响

用粉末冶金法制造了碳纤维分布均匀的碳纤维一铜复合材料，测定了复合材料的力学性能和物理性能，表明在碳纤维与铜基体之间存在界面结合，碳纤维含量对复合材料性能影响极大。     

Behavior of high performance fiber reinforced cement composites under multi-axial compressive loading

Experiments were conducted to better understand the behavior of strain hardening, high performance fiber reinforced cement composites (HPFRCC) when subjected to uniaxial, biaxial, and triaxial compression. The experimental parameters were: type of fiber, fiber volume fraction, and loading path. Two types of commercially available fibers, namely high-strength hooked steel fiber and ultra high molecular weight polyethylene fiber, with volume fractions ranging from 1.0% to 2.0%, were used in a 55-MPa mortar matrix. The selected loading paths consisted of uniaxial compression and tension, equal biaxial compression, and triaxial compression with two levels of lateral compression. The test results revealed that the inclusion of short fibers can significantly increase both strength and ductility under uniaxial and biaxial loading paths, but that the role of volume fraction is rather small for the range of fiber volume contents considered. The results also showed that the confining effect introduced by the fibers becomes minor in triaxial compression tests, where there is relatively high external confining pressure. The experimental information documented herein can serve as input for the development of multiaxial constitutive models for HPFRCCs.     

Mechanical properties and corrosion behavior of lead-silicon carbide fiber and lead-carbon fiber composites made by electrodeposition

Multifilament silicon carbide fibers (Nippon Carbon, Nicalon type) and carbon fibers (Thornel, Pan T 300 and Pitch type) were used to produce lead-matrix composite materials for battery plate grid applications. Lead was impregnated into the fibers by electrodeposition from fluoborate baths. The electrical conductivity of carbon fibers was sufficient for direct electroplating; silicon carbide fibers were electroless plated with copper beforehand. The experimental conditions for good penetration of lead into the fiber tows were determined.Unidirectional composite samples with a fiber volume fraction of 5 to 25% were prepared from both lead impregnated fiber sheets and rods by hot-pressing (280°C, 50 MPa, 5–30 mm). The flexural strength and modulus of these samples were measured as a function of the infiltration current density and of the fiber volume fraction. Ultimate strengths in the range 300–400 MPa were attained for both lead-silicon carbide and lead-carbon composites, at a fiber volume fraction of about 25%. These latter composites exhibited a good corrosion resistance towards 38.5 wt-% sulfuric acid under non-anodic conditions.     

Electrical conductivity and mechanical properties of multiwalled carbon nanotube-reinforced polypropylene nanocomposites

In this paper, the electrical conductivity and mechanical properties such as elastic modulus of multiwalled carbon nanotubes (MWCNTs) reinforced polypropylene (PP) nanocomposites were investigated both experimentally and theoretically. MWCNT-PP nanocomposites samples were produced using injection mold at different injection velocities. The range of the CNT fillers is from 0 up to 12?wt%. The influence of the injection velocity and the volume fraction of CNTs on both electrical conductivity and mechanical properties of the nanocomposites were studied. The injection speed showed some effect on the electrical conductivity, but no significant influence on the mechanical properties such as elastic modulus and stress-strain relations of the composites under tensile loading. Parallel to the experimental investigation, for electrical conductivity, a percolation theory was applied to study the electrical conductivity of the nanocomposite system in terms of content of nanotubes. Both Kirkpatrick (Rev Mod Phys 45:574?C588, 1973) and McLachlan et?al. (J Polym Sci B 43:3273?C3287, 2005) models were used to determine the transition from low conductivity to high conductivity in which designates as percolation threshold. It was found that the percolation threshold of CNT/PP composites is close to 3.8?wt%. For mechanical properties of the system, several micromechanical models were applied to elucidate the elastic properties of the nanocomposites. The results indicate that the interphase between the CNT and the polymers plays an important role in determining the elastic modulus of the system.     

用交流阻抗法研究碳纤维混凝土导电性

随着水泥基材料的发展 ,人们对水泥基材料提出的更新的要求 ,其中水泥基导电复合材料的研究引起了广泛的兴趣。制备水泥基导电复合材料的方法是在水泥基材料中掺入各种导电组分 ,目前较常用的是掺入碳纤维 ,它不仅可以大幅度提高水泥基复合材料的电导率 ,还能够改善水泥基材料的力学性能、增加其韧性。本研究主要通过对碳纤维混凝土的交流阻抗谱进行分析 ,研究其导电性能与内部微结构的关系。     

碳纤维含量对短碳纤维-铜复合材料性能的影响

用粉末冶金法制造了碳纤维分布均匀的碳纤维一铜复合材料,测定了复合材料的力学性能和物理性能,表明在碳纤维与铜基体之间存在界面结合,碳纤维含量对复合材料性能影响极大。     

碳纤维增强铜基复合材料的性能研究

采用粉末冶金法制备了短碳纤维增强铜基复合材料。经对不同碳纤维含量试样的硬度及导电性能的测定，并在干摩擦的条件下研究了碳纤维增强铜基复合材料的摩擦磨损性能，同时对磨损表面的微观结构进行观察来分析其磨损机理。实验结果表明，随着碳纤维含量的增加，该材料的硬度和耐磨性均有所增加，但其导电性有所下降。     

碳纤维增强油井水泥石的力学性能

油井水泥石在井下易脆裂,造成油井层间封隔失效,进而影响油井开采。为了解决这一问题,需要对水泥石进行降脆增韧。首先,考察了甲基纤维素和羧甲基纤维素对碳纤维的分散效果;然后,研究了碳纤维对油井水泥石抗压强度、抗折强度和劈裂抗拉强度的影响,并模拟井下环境测试了水泥石单轴和三轴应力-应变曲线;最后,使用扫描电子显微镜对碳纤维增强水泥石的微观形貌进行观察,探讨碳纤维对水泥石的增韧机制。结果表明:0.2wt%的羧甲基纤维素溶液可有效分散碳纤维;养护28d后,0.3wt%碳纤维增强水泥石的抗压强度、抗折强度和劈裂抗拉强度较纯水泥石的分别提高8.6%、31.5%和52.4%,三轴直接加载条件下,其弹性模量较纯水泥石的低49.5%;经过分散的碳纤维在水泥石中乱向分布,形成三维网络结构,通过桥联、剥离及拔出耗能作用增强水泥石。研究结果为解决油井水泥石易脆裂的问题提供了理论参考。     

A study on the DC electrical properties of PAN-based carbon fiber/polycarbonate composites

The DC conductivity and Hall effect studies were used to investigate the nature, type, and development of the charge carriers in conductive polymer composite containing PAN-based carbon fibers of different concentration. The dependence of the electrical conductivity on temperature is characterized by a two-stage electrical conduction process with a semiconducting type of behavior and two activation energies. It was found the measured Hall voltage varies linearly with Hall current with two different signs of slopes. This suggests that a composite of low fiber content is functioning as p-type material, and then changes to n-type with increasing the carbon fiber content more than 15 wt.%. The density of the charge carriers increases with carbon fiber content in a behavior similar to the electrical conductivity for all given composites, showing a percolation phenomenon. The calculated charge carriers density includes both the magnetostatic arising from the polycarbonate matrix and from the free charge carriers themselves. Considering the filled carbon fibers as a random semiconducting material, the results obtained for various composites were described in terms of the band structure model. Other approach of results analysis was based on the composite bulk morphology observed by the SEM microscopy.     

Theory of piezoresistivity for strain sensing in carbon fiber reinforced cement under flexure

A theory is provided for piezoresistivity in carbon fiber reinforced cement (with and without embedded steel reinforcing bars) under flexure (three-point bending). The phenomenon, which involves the reversible increase of the tension surface electrical resistance and the reversible decrease of the compression surface electrical resistance upon flexure, allows strain sensing. The theory is based on the concept that the piezoresistivity is due to the slight pull-out of crack-bridging fibers during crack opening and the consequent increase in the contact electrical resistivity of the fiber-matrix interface. This work is an extension of prior theory, which concerns the effect of uniaxial loading on the volume resistance. The extension requires modeling the surface resistance and its change under flexure. The theoretical results on the piezoresistivity, both with and without rebar, are in good agreement with prior experimental results. Differences between theoretical and experimental results are probably due to minor damage and rebar debonding during flexure.     

Dielectric characteristics of sisal–oil palm hybrid biofibre reinforced natural rubber biocomposites

Natural rubber was reinforced with sisal and oil palm fibers. Biocomposites were prepared by varying the weight fraction of the fibers. The dielectric properties such as dielectric constant, volume resisitivity and dielectric loss factor of the biocomposites were evaluated as a function of fiber loading, frequency and chemical modification of fibers. The dielectric constant values were found to be higher for fiber reinforced system than the gum due to polarization exerted by the incorporation of lignocellulosic fibers. Chemical modification of fibers resulted in decrease of dielectric constant values and volume resisitivity values. The volume resisitivity of the composites was found to decrease with fiber loading due to increase of hydrophilicity imparted by the lignocellulosic fibers. The dissipation factor was found to increase with fiber content.     

碳纤维增强水泥基复合材料的制备及热电性能研究

将不同含量(0.5%,1.0%,1.5%(质量分数))的碳纤维掺入到硫铝酸盐水泥基体中,制备了碳纤维增强水泥基复合材料。通过SEM、阿基米德排水测试法、四探针法等手段,研究了碳纤维含量对增强水泥基复合材料断面结构、抗弯强度、孔隙率、电导率、热导率和塞贝克系数的影响,并模拟太阳辐射进行了能量收集实验。结果表明,碳纤维均匀地分布在水泥基体中形成网格结构,碳纤维与水泥基体有很强的结合力。当碳纤维含量由0.5%(质量分数)增加到1.5%(质量分数)时,水泥基复合材料的抗压强度由71.36 MPa增加到106.51 MPa,增长了49.26%;孔隙率由0.8%增加到2.0%,增长了150.0%;电导率由0.0214 S/m增加到0.2408 S/m,增长了1025%;热导率由0.261 W/(m·K)减小到0.210 W/(m·K),减少了19.54%;塞贝克系数迅速增大,最大为1.22×10^4μV/K。当碳纤维含量为1.5%(质量分数)时,厚度为20 mm的水泥基复合材料每1 m^2可输出5~6μW的功率;在400 min辐照下,试样表面温度迅速达到70℃左右,1 m^2水泥基复合材料面板上收集到的能量高达8.1×10^-6 J。由此可知,碳纤维含量的增加,极大地提高了碳纤维增强水泥基复合材料的热电性能。     

Cement-based composites containing functionalized carbon fibers

Carbon fibers can be used to improve both mechanical properties and electrical conductivity of cement, allowing the preparation of a strengthened and toughened cement that can be used for self-monitoring applications. To guarantee both a good dispersion in water and a strong interaction with cement, surface functionalization of carbon fiber surface by reaction with acid was preferred to the use of a dispersing agent. The best oxidation conditions were chosen by using a Taguchi approach, and the samples contained the treated fibers were subjected to both mechanical and electrical tests, to determine flexural strength, toughness, compressive strength and electrical conductivity. It was shown that a not-too-strong oxidation by piranha solution was very effective to obtain well-dispersed fibers and a cement-composite with improved mechanical properties (in particular toughness) and electrical conductivity.