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为验证超声检测残余应力的精度与检测深度问题,该文提出并设计一种能够施加定值载荷应力的U形试块来模拟构件中的残余应力。通过残余应力超声检测系统激励5 MHz、4 MHz等其他不同频率的超声换能器,对U形试块在缺口施加拉压载荷,使试块处于闭合、张开的不同状态来模拟构件中的拉压状态,对U形试块的上表面不同位置和后侧面不同深度处的应力值进行超声残余应力无损检测。同时将其检测结果与同等条件下ABAQUS有限元仿真分析的结果进行对比,验证该系统对表面残余应力及试块内部梯度残余应力检测的准确性。另外,该试块也为残余应力超声检测系统的校准提供方法。 相似文献
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炭纤维水泥基复合材料eebeck效应 总被引:13,自引:1,他引:12
发现特制纤维水泥具有Seebeck效应,研究结果表明,它对温差有较高的灵敏度,试块上下表面浊国差△t与浊国差电动热呈线性关系。 相似文献
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为了探索三维石墨烯-碳纳米管(G-CNTs)/水泥净浆的压敏性能,采用四电极法研究了荷载作用下GCNTs/水泥净浆的电阻率变化,并分析不同G-CNTs掺量、加载幅度、加载速度以及恒定荷载对电阻率变化的影响。研究表明:随着G-CNTs掺量的增加,电阻率呈先减小后稳定的变化趋势,在G-CNTs掺量由0.2wt%增加至1.6wt%时,电阻率下降51.8%;电阻率与温度呈负相关;G-CNTs掺量高于0.8wt%时可以显著提高水泥净浆的压敏性能,且电阻率变化率与应力应变有明显的对应关系,1.2wt%G-CNTs掺量下试件的应力灵敏系数和应变灵敏系数分别为2.3%/MPa和291;G-CNTs/水泥净浆电阻率变化率幅值随着加载幅度增大而相应增加,其电阻率变化率曲线在不同加载速度以及恒定荷载作用下均与应力-应变曲线一一对应,具有良好的压敏特性。 相似文献
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将钢渣压制成一定形状的试块,分别在60℃、90℃及120℃下采用CO_2对试块进行了碳化处理。对碳化后试块的质量、体积、抗压强度的变化进行了测试。采用X射线能谱仪(XRD)、热重-差热分析仪(TG-DSC)分析了碳化过程中的物相变化。用扫描电子显微镜(SEM)观察了碳化后产物的微观形貌。研究结果表明,在60℃、90℃、120℃碳化温度下碳化7d后,试块的质量分别增加15.30%、17.48%、23.84%;试块的体积分别增加5.9%、6.5%、11.44%;试块的抗压强度分别达到32.87 MPa、39.62 MPa、42.38 MPa。钢渣碳化后产物主要为CaCO_3。从碳化后试块的力学强度和节能两方面综合考虑,碳化的最佳温度为90℃。 相似文献
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为研究平行于炮孔的软弱夹层对岩石爆破裂纹扩展的影响,通过制作含不同软弱夹层的水泥砂浆试块进行爆破模拟试验,并用高速摄影仪对试块爆破裂纹扩展过程进行观测。同时,通过有限元分析软件ANSYS/LS-DYNA对含不同软弱夹层试块的爆破裂纹扩展起因进行数值模拟分析。结果表明:随着软弱夹层强度的降低,软弱夹层侧爆炸反射应力波强度逐渐增加、透射应力波强度逐渐降低,这使得软弱夹层侧裂纹扩展速度逐渐增加、裂纹扩展也越充分。同时,随着软弱夹层强度的降低,爆炸应力波在软弱夹层侧的衰减速度逐渐加快。试验结果与数值模拟结果具有较强的一致性,表明数值模拟对实践具有一定的指导意义。 相似文献
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《Cement and Concrete Composites》2007,29(5):377-382
Carbon nanotubes (CNTs) treated by using a mixed solution of H2SO4 and HNO3 were uniformly dispersed into cement paste by means of ultrasonic energy. Electrical resistivity and pressure-sensitive properties under cyclic compressive loading of this composite were analyzed and compared to that of untreated-CNT reinforced cement paste. Results show that the addition of treated or untreated CNTs to cement paste leads to a notable decrease in volume electrical resistivity and a distinct enhancement in compressive sensitivity. The microstructures of these cement composites were analyzed by using scanning electron microscope. The microscopic observation reveals that both treated and untreated CNTs were dispersed homogenously in the cement matrix. For untreated CNT-reinforced cement composites, the CNTs with glossy surface were zigzag and cling to cement matrix; the bridging of cracks and a well three-dimensional meshwork were also observed. For treated-CNT reinforced cement composites, the surface of CNTs was covered by C–S–H, which leads to a higher mechanical strength. The contact points of the treated-CNTs in composites were much fewer than that of the untreated-CNTs in cement matrix composites, which leads to a higher compressive sensitive properties and a lower electrical conductivity. 相似文献
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The purpose of this paper is to investigate the setting process and evolution of electrical resistivity of Portland cement pastes with constant water to cement ratio (w/c) of 0.3 and with different dosages of naphthalene superplasticizer (SP) from 0 to 1.2 %. The setting process of cement paste was monitored by the Vicat needle test. The depth of penetration was recorded and used to calculate the shear resistance generated by the cement paste. Electrical resistivity was measured by a non-contacting electrical resistivity apparatus. The hyperbolic curve of electrical resistivity versus time was plotted to determine the ultimate electrical resistivity. The results show that the addition of SP to the pastes with a fixed w/c can cause longer setting time and delay the evolution of electrical resistivity. The final setting time (t f) and the occurring time of maximum rate of electrical resistivity (t r) were both delayed when the dosage of SP was increased. This may indicates that the electrical resistivity measurement can be used to monitor the setting process of cement. The compressive strength at 28 days and the ultimate electrical resistivity show a same tendency for the cement pastes with different dosages of SP. Thus, it would be possible to predict the compressive strength of hardened cement paste by its ultimate electrical resistivity. 相似文献
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Zhenghong Tian Ce Bian Zhihai Peng 《International Journal of Pavement Engineering》2016,17(9):789-798
The effect of moisture content on the compressive mechanical behaviours of cement mortar under different high strain rates is studied in this paper. The rapid impact testing, i.e. the strain rates of 80, 100, 150, 200 and 250 s? 1 by Split Hopkinson pressure bar, on number of specimens with special water/cement ratio of 0.50 and saturations as 0%, 25%, 50%, 75% and 100%, respectively, was executed. The dynamic compressive behaviours were analysed in terms of the maximum stresses, elastic modulus, critical strain at maximum stresses and ultimate strains at failure. Results indicated that similarity existed in the shape of strain–stress curves of mortars with different moisture subjected to different strain rates of impact loading, i.e. the upward section presented bilinear characteristics, while the descending stage was almost linear. As strain rate increases, the dynamic compressive strength, elastic modulus and critical strain at maximum stress increase which can be ascribed to the dynamic fracture effect and the microscope inertia effect. Besides, it was shown that desiccation provokes an increase in mortar strength and deformation behaviour of the studied mortar with different saturation caused by capillary depression and microcracking. Drying effect has to be considered in modelling of the coupling between desiccation and mechanical behaviour of the mortar. Finally, the multi-parametric statistical analysis of water content and strain rate on the mechanical behaviours of cement mortar subjected to dynamic loading is detailed. 相似文献
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为探讨乙炔炭黑水泥基复合材料的压敏性 , 验证了利用基于埋入式环状电极的四电极法测试复合材料电阻的可行性; 研究了一次加载至破坏时乙炔炭黑水泥基复合材料的电阻率变化规律 , 并通过在弹性阶段的加载考察了乙炔炭黑水泥基复合材料压敏性的重现性 ; 分析了测试电流和试件偏压对压敏性的影响。研究结果表明 ,基于埋入式环状电极的四电极法测试压敏水泥基材料的电阻误差小于 10 % , 用于复合材料电阻的测试是可行的。掺量 15 vol %的乙炔炭黑水泥基复合材料一次加载至破坏 , 电阻率变化率最大可达 55 % , 弹性阶段电阻率变化率可达 35 %以上 , 且其压敏性基本不受测试电流和试件偏压的影响。乙炔炭黑是制备具有高感知灵敏度的压敏水泥基材料的一种有效功能组分。 相似文献
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Compressive strength and electrical properties of concrete with white Portland cement and blast-furnace slag 总被引:1,自引:0,他引:1
A. LübeckA.L.G. Gastaldini D.S. BarinH.C. Siqueira 《Cement and Concrete Composites》2012,34(3):392-399
Electrical resistivity is an important characteristic of concrete because it allows evaluation of the accessibility of aggressive agents prior to the beginning of the corrosive process and estimation of the corrosion propagation. This study investigated the apparent electrical resistivity of concrete mixes with white Portland cement and with and without blast-furnace slag using Wenner’s four-electrode method. The compressive strength of concrete cylinders and the electrical conductivity of the pore solution were tested. Examined slag contents were 50% and 70% by mass and the results were compared to reference mixtures of 100% white Portland cement and 100% grey Portland cement, as well as to mixtures with equal percentages of slag and grey Portland cement. Larger amounts of slag resulted in increased electrical resistivity and decreases in the electrical conductivity of the pore solution, when compared to the reference concretes. The mixture made of 50% slag and 50% white Portland cement showed, on average, compressive resistance levels between 35 MPa and 60 MPa, electrical resistivity values that were approximately five times greater, costs that were 14.6% less per m3, and whiteness similar to the reference concrete. These results indicate that white Portland cement can be partially substituted by blast-furnace slag. 相似文献
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RuOx thin films have been deposited by reactive sputtering in an O2/Ar atmosphere. The films were characterized for their stress and resistivity as a function of deposition temperature (room temperature, 300°C) and the O2 content (25–100%) in the sputtering gas. Additionally, the stresses in these films were determined as a function of annealing temperature (up to 600°C) using an in-situ curvature measurement technique. The as-deposited films were found to be under a state of compressive stress for all deposition conditions. The compressive stresses sharply increased with increasing deposition temperature from a value of around 200 MPa at 200°C to 1400 MPa at 300°C. This dramatic increase has been attributed to differences in microstructure at these deposition temperatures. The microstructural differences also led to the widely differing stress-temperature behavior during annealing of these films. For films deposited at temperatures lower than 200°C, the annealing process resulted in a decrease in the compressive stress and resistivity of the films. However, films deposited at a temperature of 300°C did not show any changes in the compressive stress or resistivity after annealing. The results of this study can be used to deposit RuOx thin films with low resistivity and minimal stresses. 相似文献
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This paper investigates the effects of nano-kaolinite clay (NKC) on the freezing and thawing (F–T) behavior of concrete. In our experiments, we substituted NKC for 0%, 1%, 3%, and 5% of mixtures of ordinary Portland, cement, by weight. The blended concrete was prepared using w/c ratio as 0.5. A rapid freeze–thaw Cabinet was then used to measure the resistance of ordinary Portland cement concrete, as opposed to the concrete/NKC mixture, to examine deterioration caused by repeated F–T actions. We regularly measured the properties of the concrete specimens, including the pore structure, mass, electrical resistivity, chloride diffusion coefficient, compressive strength and dynamic modulus of elasticity. A computed tomography scan test evaluated the porosity characteristics of the concrete. This paper also applied scanning electron microscopy and X-ray diffraction tests in order to investigate the micro morphology and chemical element distributions inside of the concrete. The experimental results and visual comparisons revealed that the introduction of NKC improves the F–T resistivity values, as compared to the control concrete. The samples with 5% NKC exhibited the highest compressive strength, chloride diffusion resistivity, relative dynamic modulus of elasticity, and the most electrical resistivity after 125 F–T cycles. We designated the anti-freezing durability coefficient (DF) as the index to assess the F–T resistivity of concrete. The following research discusses the relationship between the concrete’s DF and the number of F–T cycles, compressive strength, chloride diffusion coefficient, and the electrical resistivity of the concrete samples. 相似文献
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《Cement and Concrete Composites》2005,27(4):449-461
This paper presents the results of an experimental investigation on the steel reinforcement corrosion, electrical resistivity, and compressive strength of concretes. Concretes having two different water–cement ratios (0.65 and 0.45) and two different cement contents (300 and 400 kg/m3) were produced by using a plain and four different blended portland cements. Concrete specimens were subjected to three different curing procedures (uncontrolled, controlled, and wet curing). The effect of using plain or blended cements on the resistance of concrete against damage caused by corrosion of the embedded reinforcement has been investigated using an accelerated impressed voltage setup. The resistivity of the cover concrete has been measured non-destructively by placing electrodes on concrete surface. The compressive strength, electrical resistivity, and corrosion resistance of the concretes were determined at different ages up to 180 days. The results of the tests indicated that the wet curing was essential to achieve higher strength and durability characteristics for both plain and especially blended cement concretes. The concretes, which received inadequate (uncontrolled) curing, exhibited poor performance in terms of strength and corrosion resistance. 相似文献
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Abstract: The propagation of fatigue cracks under constant amplitude cyclic loading was studied in welded stiffened steel plates. The residual stresses in the stiffened plates were measured using the neutron diffraction strain‐scanning technique. The neutron diffraction measurements indicated that, in general, the residual stresses were tensile near the welded stiffeners and compressive between the stiffeners and ahead of the starter notch tips. Fatigue testing indicated that the fatigue crack growth rates of the stiffened plates were, in general, lower than that of a corresponding unstiffened plate, especially near the notch tips, where compressive residual stresses existed. An analytical method, using Green's function, was developed to predict the fatigue crack growth rates. Reasonable accuracy was obtained. 相似文献