Coaxial Test Research Articles

Effect of fiber orientation on the structural behavior of FRP wrapped concrete cylinders

In this study, 27 concrete cylinders with a diameter of 152.4 and a height of 304.8 mm were prepared. Among them, 18 cylinders were wrapped using two layers of fiber reinforced polymer (FRP) with six fiber orientations; six cylinders were wrapped using four layers of FRP with fibers in axial or hoop direction only; the remaining three cylinders were used as control. The FRP used was E-glass fiber reinforced ultraviolet (UV) curing vinyl ester. Fifteen coupon specimens were prepared to experimentally determine the tensile strength of the FRP with fibers oriented at 0°, 45°, and 90° from the loading direction. Co-axial compression tests were conducted on the wrapped cylinders and control cylinders. The test results were compared with existing confinement models. It is found that the strength, ductility, and failure mode of FRP wrapped concrete cylinders depend on the fiber orientation and wall thickness. Fibers oriented at a certain angle in between the hoop direction and axial direction may result in strength lower than fibers along hoop or axial direction. A larger database is desired in order to refine the existing design-oriented confinement models.

Steady and transient flow behaviour of fresh cement pastes

Fresh cement pastes behave as non-Newtonian viscous fluids. During steady flow, their apparent viscosity depends on the applied strain rate. During transient flow, the apparent viscosity is a function of time. In this work, a thixotropic model is presented. Its four parameters are identified experimentally for a tested cement paste using coaxial viscometer test. Viscometer flow simulations are then carried out. The model proves to be able to predict the trends of the fresh behaviour of cement pastes in various flow situations.

Extended numerical modeling and application of the coaxial shear test for asphalt pavements

Coaxial Shear Test (CAST) is used at EMPA road engineering center for determining the mechanical properties of asphalt concrete under repeated sinusoidal loading in both load and strain controlled mode at different temperatures and frequencies. CAST provides stiffness information under lateral deformation confinement, thus simulating the situation in a pavement layer under an idealized traffic loading. In order to understand the complex behavior of the system, Finite Element Analysis (FEA) of the complete test setup was carried out. The details of the FEA model as well as the data analysis procedure are described. New types of experiments, carried out with the CAST equipment, such as the determination of the water sensitivity under combined cyclic mechanical and temperature loading, are described. The distinctive features of the implementation and evaluation of the mechanical properties from experiments are discussed.

Influence of water and temperature on mechanical properties of selected asphalt pavements

One of the main causes of distress in asphalt pavements is water damage. The purpose of this paper is to compare different test methods to evaluate moisture susceptibility. This is of special importance because of the insufficient effectiveness of the test procedures currently used. In this research, experiments were conducted to investigate the effects of water and temperature on mechanical properties of mixtures with different, air void content. The evaluation of such properties concentrates on the following three approaches: innovative (Coaxial Shear Test), traditional, (Indirect Tensile Test) and empirical (Cantabro Test). Specimens were prepared by means of Superpave Gyratory Compactor (SGC) and divided in two different subsets for controlled dry and wet conditioned testing. Test results indicated that the Indirect Tensile Test (IDT) is not able to discriminate between wet and dry condition as the Coaxial Shear Test (CAST) does. The CAST method reproduces closest the real field conditions and indicates clearly the risk of water damage for open graded mixtures (high air void content). Dense graded mixtures (low air void content) showed less influence probably due to the reduced amount of penetrating water. Cantabro Tests (CAT) provided also significant results in good correlation with air void content and material properties of asphalt mixes.

Extended numerical modeling and application of the coaxial shear test for asphalt pavements

The International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM) was founded with the aim to promote scientific cooperation in the area of construction materials and structures worldwide. This mission is achieved through collaboration of leading experts in construction practice and science including academics, researchers, industrialists, testing laboratories and authorities.

Far-Field Acoustic Investigation into Chevron Nozzle Mechanisms and Trends

Chevron nozzles currently offer one of the most feasible methods of reducing jet exhaust noise in medium to high-bypass turbofan engines. Tests were conducted in the University of Cincinnati Nozzle Acoustic Test Facility, simulating a separate flow exhaust system to provide insight into some of the basic mechanisms and trends of this emerging technology. For this study, a baseline inner nozzle and three chevron nozzles were tested over a wide range of operating conditions, including dual and single flow. Chevrons with varying numbers of lobes and levels of penetration were selected for this study to provide insight into the impact of these geometric parameters on the noise level. Spectral and directivity results from heated, coaxial flow tests showed that the chevron nozzles are most effective at lower frequencies and at aft directivity angles. Reductions in overall sound pressure level (SPL) ranging from 3 to 6 dB were documented. Calculations of perceived noise level directivity also showed 4-6 dB reduction at aft angles. The data also illustrated clear and consistent trends with respect to the chevron geometric parameters. Specifically, the chevron penetration was determined to be a primary factor in controlling the tradeoff between low-frequency reduction and high-frequency SPL increases. Although slight differences were observed with varying chevron lobe numbers at a fixed penetration, it appears that the effect is less significant than the penetration. Finally, the data indicated clear dependence of the chevron benefit on the velocity difference between the inner and outer streams.

Traveling wave resonant ring for electron cloud studies

Within the framework of the CERN program on electron cloud effects in accelerators, a coaxial multipacting test stand was built. In order to simulate bunched beam, the test stand is subjected to short rf pulses. The field strength in a traveling wave mode is sufficient to trigger multipacting in ``as received'' surfaces, but not in chambers treated to reduce the secondary emission yield. Thus a number of upgrades in the bench setup have been pursued, mainly in two directions. The first one is a general reduction in mismatching (i.e., electrical losses) amongst the different parts of the setup. Secondly, instead of dumping the pulsed power into a load, it is recirculated by means of a broadband working regime resonant ring. This ring required the design of a directional coupler with up to 1 kV dc isolation, very low transmission losses, and a four octave bandwidth. This paper reports on the steps required to build this traveling wave resonant ring (improvements on the chamber and implementation of the coupler) and includes an appendix on the main properties of the setup that relate to electron multipacting studies.

“Galileo Galilei (GG) on the Ground-GGG”: experimental results and perspectives

The GGG differential accelerometer is made of concentric coaxial test cylinders weakly coupled in the horizontal plane and spinning in supercritical regime around their symmetry axis. GGG is built as a full scale ground based prototype for the proposed “Galileo Galilei-GG” space experiment aiming to test the equivalence principle (EP) to 10 −17 at room temperature. We report measured Q values of 95000 at 1.4 Hz, and expect even better ones at typical spin frequencies of a few Hz. An EP violation signal in the field of the Sun would appear as a low frequency displacement in the horizontal plane of the laboratory, and it can be separated out from a much larger whirl motion of the test masses at their natural differential frequency. So far we have managed to reduce the amplitude of this whirl to about 0.1 μm. We discuss how to improve these results in view of the very high accuracy GG experiment in space, and/or to reach a 10 −13 sensitivity in the lab which would allow us to either confirm or rule out recent predictions of violation to this level.

High-frequency input impedance characterization of dielectric films for power-ground planes

Broadband impedance characterization of high dielectric constant (high-k) films was performed using a coaxial test fixture configuration. The presented coaxial test fixture and broadband measurement methodology of impedance for high-k films minimizes systematic uncertainties by reducing the interconnection inductance and improving the calibration procedure. In the APC-7 configuration, the technique enables accurate evaluation of impedance at frequencies of 100 MHz to 10 GHz with resolution of 0.01 /spl Omega/. The electrical characteristic of high-k films was found to be consistent with a capacitive load without significant contribution from the circuit inductance that typically dominates the high-frequency response. The experimental data and numerical simulations showed that high-k organic-ceramic composite materials could considerably suppress resonant behavior of the power-ground planes. It was found that high-k organic resins filled with ferroelectric ceramic powders exhibit a high-frequency dielectric loss that increases with increasing volume fraction of the ceramic component. The dielectric dispersion and the corresponding dielectric loss of organic-ceramic hybrid materials can serve as an effective mechanism for suppressing the resonant standing waves in power-ground planes.

Effect of injected charge on the electrification of oil flowing past the surface of composite polymers

AbstractThe factors affecting oil‐flow electrification (OFE) in large forced oil‐cooled electric power apparatus are experimentally investigated using a closed cycle model, and a coaxial test section comprising a charge injector. The streaming and leakage currents are measured to investigate the impact of injected charge on OFE interfaced with composite polymers. The results reveal that the magnitude and polarity of the injected charge, and the type of composite polymer and its impregnation resin, if it exits, cause evident qualitative as well as quantitative changes in the measured currents. Cellulose‐based materials give the highest leakage current. For other composite polymers, the higher the number of ketonic carbonyls and/or delocalized states in the aromatic moieties, the higher is the leakage current, and hence the lower is the streaming current. Under flow conditions, the leakage current is lower than that under a stationary condition, but the trend is reversed at high temperature, especially for the HVDC case. Under HVAC, the streaming current shows polarity reversal from negative to positive on increasing the oil temperature and/or voltage. For HVDC application, the streaming current is significantly reduced by calendering the outermost layer of the composite polymer, using fine glass as a backing material instead of using glass fabric, and impregnating the composite polymer with highly dipolar epoxy resin.

Towards a `smart window' for microwave applications

Discs of poly(aniline)-silver-polymer electrolyte particulate composites exhibit rapid and reversible changes in their microwave impedance when small electric fields are applied across them in a coaxial line test set in a resonant condition. The effect of composition on the cyclic voltammetry and microwave characteristics of the composites is described. The experimental data show that changes in the gradients of the cyclic voltammograms coincide with large changes in microwave resonant null depth consistent with increasing conductivity of the composite when the fields are applied during electrochemical cycling. The reverse change occurs when the field is removed. An equivalent network model comprising a parallel resistor and capacitor has been fitted to the measured data. Scanning electron microscopy studies on both the cycled and uncycled composites are presented and suggest that, during cycling, the silver metal dissolves and is then re-precipitated.

Heat transfer augmentation by coiled wire inserts during forced convection condensation of R-22 inside horizontal tubes

In the present work, heat transfer augmentation by coiled wire inserts during forced convection condensation of R-22 inside horizontal tubes has been studied. The test-condenser consisted of four separate coaxial double pipe test sections assembled in series. It was a counterflow heat exchanger where R-22 condensed inside the inner tube by rejecting heat to the coolant water flowing in the annulus. Coiled wires with three different wire diameters of 0.65, 1.0 and 1.5 mm and three different coil pitches of 6.5, 10.0 and 13 mm were made and used in full length of test-condenser. The use of helically coiled wires were found to increase the condensing heat transfer coefficients by as much as 100% above the plain tube values on a nominal area basis.

Control of microwave reflectivities of polymer electrolyte-silver-polyaniline composite materials

Discs of composites of particular poly(aniline hydrochloride) or poly(aniline hydrotetrafluoroborate) and silver in a poly(ethylene oxide)-AgCF 3SO 3 polymer electrolyte were characterized using microwaves over the frequency range 0.5–3.0 GHz in a coaxial line. The materials demonstrated a rapid and reversible change in their microwave reflectivity when a dc potential of 5 volts was applied across them. A coaxial line test set was used to observe changes of 15–20 dB in microwave reflectivities and displacements of ca 0.25 GHz in the resonance condition. The observations are tentatively discussed in terms of reversible changes in conductivities of the particulate components and the capacitance within ‘microcells’ of polyaniline/polymer electrolyte/silver.

Optimum conditions of electroless nickel plating on carbon fibres for EMI shielding effectiveness of ENCF/ABS composites

Nickel coated carbon fibres, the best conductive fillers for electromagnetic interference (EMI) shielding, were produced by electroless nickel plating. The carbon fibres, T300C and T700SC, were plated at different workloads, pH values and temperatures of plating bath, and were used for preparing composites of acrylonitrile–butadiene–styrene by polymer blending to test the EMI shielding effectiveness (SE) by the coaxial transmission line test method. The best SE (44 dB) was reached by the deposition conditions of workload=2 g/L, pH 9 and temperature 70°C.

Modeling of the Radio Frequency Electric Field Strength Developed During the Rf Assisted Heat Pump Drying of Particulates

A new “boundary value” approach to model the radio frequency (rf) electric field strength during the tf assisted drying of particulate materials has been developed and validated with experimental data. Material dielectric data at varying moisture contents and elevated temperatures were measured in a novel co-axial test cell and used in the analysis. Experimental drying results are presented showing how the simultaneous application of if heating complements heat pump drying, not only increasing drying rate, but also increasing the heat pump coefficient of performance.

Tailoring the microwave permittivity and permeability of composite materials

The microwave permittivity (ɛr) and permeability (µr) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of ɛ′, e″, µ′, µ″ as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ɛr if the filling factor is less than 0.30 and ratio |ɛ1| (host)/ |ɛ2| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ɛ2 and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that the MG theory was unable to model µr. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites.

The excitation of UHF signals by partial discharges in GIS

The fundamental theory of the UHF method for detecting partial discharge (PD) in gas insulated substations (GIS) is presented. The effects of position, size, current amplitude and pulse shape of the PD source on the UHF signal can be predicted using this theory. Excitation of propagating electromagnetic waves by a PD current pulse within the coaxial waveguides formed by GIS components is explained by making use of dyadic Green's functions for the electric fields of propagating modes. Experiments with a coaxial test chamber are used to verify the theoretical predictions, and comparisons are made between measured and simulated UHF signals. Some implications for the UHF measurement of PD are discussed, together with positioning and sensitivity requirements for UHF couplers. A scheme is proposed for standardizing PD measurements made using the UHF technique.

Control of conductivity at microwave frequencies in a poly(aniline hydrochloride)-silver-polymer electrolyte composite material

The fabrication of a conducting polymer-silver-polymer electrolyte composite material is described. Discs of the material mounted in a coaxial test fixture exhibit changes in their microwave impedance caused by an applied DC electric field. An explanation for the observed phenomena in terms of an electrochemical cell is suggested.

Mechanisms of graphite formation from kerogen: experimental evidence

To resolve the role of strain in the formation of natural graphite, a ‘hard’ carbon-based anthracite and a ‘soft’ carbon-based high volatile bituminous coal were deformed in hydrostatic, coaxial and simple shear configurations at temperatures up to 900°C and confining pressures up to 1 GPa. Additional tests were carried out at ambient pressures at temperatures up to 2800°C. In simple shear, graphite appears, with an anthracite starting material at temperatures as low as 600°C; samples tested at 900°C are predominately graphitized, as is evident from optical microscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). In tests on high volatile bituminous coal, graphite first appears in simple shear tests at temperatures of 800°C and is common at 900°C. In TEM observations graphite particles are lamellar, have punctual hkl reflections or Debye-Scherrer hkl rings (triperiodic order) and long, stiff and stacked lattice fringes typical of well crystallized graphite. No graphite was formed in either the hydrostatic or coaxial tests (they remain porous and turbostratic). Micro-Raman spectroscopy of deformed samples indicates the presence of defects (Band at 1350 cm −1) even in samples that prove to be mainly graphite by XRD and TEM. With increasing experimental temperatures there is an overall increase in maximum reflectance and bireflectance. Samples deformed in simple shear locally have reflectance values typical of graphite. In anthracite the highest reflectance and bireflectance values occur in zones of kink banding or cataclasis, indicating the importance of localized areas of high strain on graphitization. In high volatile bituminous coal localization of graphite appears to reflect compositional heterogeneity as well as strain partitioning during the experiments. The occurrence of low reflectance zones and mesoporous-turbostratic particles in samples otherwise composed of graphite is interpreted as reflecting localized areas of low strain (strain shadows) during deformation. Comparison of anthracite and high volatile bituminous coal samples tested under the same general conditions indicate that anthracite is more graphitizable under all conditions. The importance of simple shear experiments is that, because of their geometry, a significant component of strain is imparted to the samples. Strain energy has facilitated additional flattening of existing pores, with likely mechanical rotation of stacks of basic structural units (BSUs) and rupturing of pore walls. Thus, strain facilitates coalescence of pores, parallelism of BSUs and, therefore, the growth of aromatic sheets (by coalescence of neighbouring pores), leading to the formation of graphite. We propose that a major component of the activation energy required for graphitization in our experiments and, by analogy, in nature, is provided by strain energy.

A fast transient test module for ZnO surge arresters

The module is a low-inductance coaxial test facility incorporating integral voltage and current transducers. It allows measurements up to 50 kV at 1 kV ns-1 and 5 kA at 10 A ns-1. Tests with 11 kV distribution surge arresters enable their dynamic voltage-current responses to be examined. No voltage overshoot is observed.