Damage Evolution of Ballastless Track Concrete Exposed to Flexural Fatigue Loads:The Application of Ultrasonic Pulse Velocity,Impact-echo and Surface Electrical Resistance Method

In order to clarify the fatigue damage evolution of concrete exposed to flexural fatigue loads,ultrasonic pulse velocity(UPV),impact-echo technology and surface electrical resistance(SR) method were used.Damage variable based on the change of velocity of ultrasonic pulse(Du) and impact elastic wave(Di)were defined according to the classical damage theory.The influences of stress level,loading frequency and concrete strength on damage variable were measured.The experimental results show that Du and Di both present a three-stages trend for concrete exposed to fatigue loads.Since impact elastic wave is more sensitive to the microstructure damage in stage Ⅲ,the critical damage variable,i e,the damage variable before the final fracture of concrete of Di is slightly higher than that of Du.Meanwhile,the evolution of SR of concrete exposed to fatigue loads were analyzed and the relationship between SR and Du,SR and Di of concrete exposed to fatigue loads were established.It is found that the SR of concrete was decreased with the increasing fatigue cycles,indicating that surface electrical resistance method can also be applied to describe the damage of ballastless track concrete exposed to fatigue loads.

The Effect of Sparger Geometry on Gas Bubble Flow Behaviors Using Electrical Resistance Tomography

By electrical resistance tomography (ERT) the cross sectional profiles of gas hold-up in a φ56mm bubble column are obtained with four designs of gas sparger. The effect of sparger geometry on the bubble distribution is re-vealed by applying a sensitivity conjugated gradients reconstruction method (SCG). Experimental results show that over-all hold-up obtained by ERT is generally in good agreement with those measured with the pressure transducer and the ERT system produces informative evidence that the radial profiles of hold-up is very similar to the sparger design in the lower section of bubble column. Meanwhile, the rise velocity of bubble swarm and the Sauter mean bubble size are evaluated using ERT based on dynamic gas disengagement theory. The experimental results are in good agreement with correlations and conventional estimation obtained using pressure transmitter methods.

Use of Electrical Resistance to Detect the Formation and Decomposition of Methane Hydrate

The changes of electrical resistance （R） were studied experimentally in the process of CH4 hydrate formation and decomposition, using temperature and pressure as the auxiliary detecting methods simultaneously. The experiment results show that R increases with hydrate formation and decreases with hydrate decompositon. R is more sensitive to hydrate formation and decompositon than temperature or pressure, which indicates that the detection of R will be an effective means for detecting natural gas hydrate （NGH） quantitatively.

Comparative investigation on copper atmospheric corrosion by electrochemical impedance and electrical resistance sensors

Electrochemical impedance(EIS)and thin electrical resistance(ER)sensors were invented for atmospheric corrosion measurement of copper(Cu)during cyclic wetting−drying/high−low temperature tests and field exposure tests.Three-month field exposure results showed that average corrosion rate of Cu measured by ER sensor was well in accordance with that by weight loss method.During cyclic wetting−drying test,EIS was proven to reflect sensitively time of wetting and drying on the surface of sensor.Although corrosion rate obtained from EIS had a similar tendency to that obtained from ER sensors,the former was more dependent on environmental humidity than the latter.When relative humidity was low than 60%,corrosion rate of Cu measured by EIS was much lower than that by weight loss method,mainly attributing to the fact that impedance sensor failed to detect corrosion current of interlaced Cu electrodes due to the breakdown of conductive passage composed of absorbed thin liquid film under low humidity condition.Promisingly,ER sensor was proven to be more suitable for atmospheric corrosion monitoring than electrochemical techniques because it could sensitively monitor thickness loss of Cu foil according to the Ohmic law,no matter how dry or wet the sensor surface is.

An adaptive electrical resistance tomography sensor with flow pattern recognition capability

The all traditional electrical resistance tomography (ERT) sensors have a static structure, which cannot satisfy the intelligent requirements for adaptive optimization to ERT sensors that is subject to flow pattern changes during the real-time detection of two-phase flow. In view of this problem, an adaptive ERT sensor with a dynamic structure is proposed. The electrodes of the ERT sensor are arranged in an array structure, the flow pattern recognition technique is introduced into the ERT sensor design and accordingly an ERT flow pattern recognition method based on signal sparsity is proposed. This method uses the sparse representation of the signal to express the sampling voltage of the ERT system as a sparse combination and find its sparse solution to achieve the classification of different flow patterns. With the introduction of flow identification information, the sensor has an intelligent function of adaptively and dynamically adapting the sensor structure according to the real-time flow pattern change. The experimental results show that the sensor can automatically identify four typical flow patterns: core flow, bubble flow, laminar flow and circulation flow with recognition rates of 91%, 93%, 90% and 88% respectively. For different flow patterns, the dynamically optimized sensor can significantly improve the quality of ERT image reconstruction.

Design of Parallel Electrical Resistance Tomography System for Measuring Multiphase Flow

ERT(electrical resistance tomography) is effective method for visualization of multiphase flows,offering some advantages of rapid response and low cost,so as to explore the transient hydrodynamics.Aiming at this target,a fully programmable and reconfigurable FPGA(field programmable gate array)-based Compact PCI(peripheral component interconnect) bus linked sixteen-channel ERT system has been presented.The data acquisition system is carefully designed with function modules of signal generator module;Compact PCI transmission module and data processing module(including data sampling,filtering and demodulating).The processing module incorporates a powerful FPGA with Compact PCI bus for communication,and the measurement process management is conducted in FPGA.Image reconstruction algorithms with different speed and accuracy are also coded for this system.The system has been demonstrated in real time(1400 frames per second for 50 kHz excitation) with signal-noise-ratio above 62 dB and repeatability error below 0.7%.Static experiments have been conducted and the images manifested good resolution relative to the actual object distribution.The parallel ERT system has provided alternative experimental platform for the multiphase flow measurements by the dynamic experiments in terms of concentration and velocity.

Detecting Impact Damage in Carbon Fabric/epoxy-matrix Composites by Ultrasonic F-scan and Electrical Resistance Measurement

The status and the variation of electrical resistance of impacted carbon fiber/epoxy-matrix composites were studied by ultrasonic F-scan and electrical resistance measurement The experimental results shows that impact damage energy threshold value of carbon fabric/epoxy-matrix composites can determine by using ultrasonic F-scan. When the impact energy exceeds the threshold value, damage is generated in composites. Electrical resistance of impacted composites is changed owing to the contact of each carbon fiber unit in composites, which cause a change of the series-parallel in conductors. The veracity of detecting impact damage in composites can be improved in this case.

Electrical resistance stability of high content carbon fiber reinforced cement composite

The influences of curing time, the content of free evaporable water in cement paste, environmental temperature, and alternative heating and cooling on the electrical resistance of high content carbon fiber reinforced cement (CFRC) paste are studied by experiments with specimens of Portland cement 42.5 with 10 mm PAN-based carbon fiber and methylcellulose. Experimental results indicate that the electrical resistance of CFRC increases relatively by 24% within a hydration time of 90 d and almost keeps constant after 14 d, changes hardly with the mass loss of free evaporable water in the concrete dried at 50 °C, increases relatively by 4% when ambient temperature decreases from 15 °C to ?20 °C, and decreases relatively by 13% with temperature increasing by 88 °C. It is suggested that the electric resistance of the CFRC is stable, which is testified by the stable power output obtained by electrifying the CFRC slab with a given voltage. This implies that such kind of high content carbon fiber reinforced cement composite is potentially a desirable electrothermal material for airfield runways and road surfaces deicing.

Comparison between the electrical resistance and the shear strength of brazed cemented carbides

Brazing is a suitable technology to join different materials such as cemented carbides and steel. Even though this technology has been investigated for many years, insufficient joints can occur easily, as the brazing process is very sensitive concerning the handling parameters. Defects such as voids and cracks are hard to detect by commonly used visual inspection methods. Other nondestructive methods such as radiography or ultrasonic testing are usually not economical for the examination of these joints. Studies proved that the electrical resistance has the potential to serve as an effective alternative for the evaluation of brazed joints. In this study, the authors have compared the electrical resistance and the shear strength. For this, cemented carbides were brazed to steel by means of induction heating at an ambient atmosphere. A silver-based filler metal （ BrazeTec 4900 / Ag 449 ） and a flux （ BrazeTec spezial h / FH12） were selected to enable the brazing process. The brazing time and the temperature were varied in order to produce different joint qualities. After brazing, the resistance was measured on each joint with the 4-point probe method to facilitate a high accuracy. The results underline the possibility to use electrical resistance measurements as an effective tool for a quality control of brazed joints.

THE INVESTIGATION OF THE METAL DAMAGE AT THE CREEP BY THE METHOD OF ELECTRICAL RESISTANCE MEASURING

In this paper the method of damage measurement of metal structure at the creep is proposed.In contrast to other methods,it allows the measurement of this damage to be carried out in the process of creep test without unloading and cooling of specimens.Experimental damage curves during creep are obtained as a result of test data processing by the suggested method.The analysis of these curves leads to a conclusion that the material damage at repture is monotonically decreasing function of the applied stress.This conclusion is an experimental verification of the theoretical result,obtained earlier.

Improving tree health assessment accuracy at low temperatures:considering the effect of trunk ice content on electrical resistance and stress wave tomography

Accurate decay detection and health assessment of trees at low temperatures is an important issue for forest management and ecology in cold areas.Low temperature ice formation on tree health assessment is unknown.Because electric resistance tomography and stress wave tomography are two widely used methods for the detection of tree decay,this study investigated the effect of ice content on trunk electrical resistance and stress wave velocity to improve tree health assessment accuracy.Moisture content,trunk electrical resistance and stress wave velocity using time domain reflectometry were carried out on Larix gmelinii and Populus simonii.Ice content is based on moisture content data.The ice content of both species showed a trend of increasing and then decreasing.This was opposite with ambient temperatures.With the decrease of temperatures,daily average ice content increased,but the range narrowed gradually and both electrical resistance and stress wave velocity increased.Both increased rapidly near 0℃,mainly caused by ice formation(phase change and freezing of free water)in live trees.In addition,both are positively correlated with ice content.The results suggest that ice content should be considered for improving the accuracy of tree decay detection and health evaluation using electric resistance tomography and stress wave velocity methods under low temperatures.

Quality Evaluation of Diffusion Bonded Joints by Electrical Resistance Measuring and Microscopic Fatigue Testing

Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems.However,the previous studies have been focused on the macro mechanical performance of diffusion bonded joint,especially diffusion bonding conditions effects on tensile strength,shearing strength and fatigue strength.The research of interfacial micro-voids and microstructures evolution for failure mechanism has not been carried out for diffusion-bonded joints.An interfacial electrical resistance measuring method is proposed to evaluate the quality of bonded joints and verified by using two-dimensional finite-element simulation.The influences of micro void geometry on increments of resistance are analyzed and the relationship between bonded area fraction and resistance increment is established by theoretical analysis combined with simulated results.Metallographic inspections and micro-hardness testing are conducted near the interface of diffusion bonded joints.For the purpose of identifying the failure mechanisms of the joints,both microscopic tensile and fatigue tests are conducted on the self-developed in-situ microscopic fatigue testing system.Based on the microscopic observations,the mechanism of interfacial failure is addressed.The observation result shows that for 316LSS diffusion-bonded joints,microstructure evolution and effect of micro-voids play a key role in interfacial failure mechanism.Finally,a new life prediction model in terms of the increment of electrical resistance is developed and confirmed by the experimental results.The proposed study is initiated that constituted a primary interfacial failure mechanism on micron scale and provide the life prediction for reliability of components sealed by diffusion bonding.

Electrical Resistance Measurement of Glass Transition and Crystallization Characteristics of Zr-Al-Cu-Ni Metallic Glasses

In this paper, glass transition and thermal stability of the Zr-AI-Cu-Ni metallic glasses were investigated by using electrical resistance measurement (ERM), DSC and X-ray diffraction techniques. The experimental results show that the ERM is capable of detecting the glass transition of the amorphous alloys and can help to distinguish the crystallization products of the Zr-AI-Cu-Ni metallic glasses owing to the difference of the electrical resistivity between the precipitation phases.

In situ electrical resistance and activation energy of solid C_(60) under high pressure

The in situ electrical resistance and transport activation energies of solid C60 fullerene have been measured under high pressure up to 25 GPa in the temperature range of 300-423 K by using a designed diamond anvil cell. In the experiment, four parts of boron-doped diamond films fabricated on one anvil were used as electrical measurement probes and a W-Ta thin film thermocouple which was integrated on the other diamond anvil was used to measure the temperature. The current results indicate that the measured high-pressure resistances are bigger than those reported before at the same pressure and there is no pressure-independent resistance increase before 8 GPa. From the temperature dependence of the resistivity, the C60 behaviors as a semiconductor and the activation energies of the cubic C60 fullerene are 0,49, 0.43, and 0.36 eV at 13, 15, and 19 GPa, respectively.

Evaluation of Impact Damage Tolerance in Carbon Fabric/epoxy-matrix Composites by Electrical Resistance Measurement

Impact damage tolerance is provided in intensity design on composites. The compression intensity of impacted composites requires more than 60% of its original intensity. The influence of impact on compressive intensity and electrical resistance of carbon fabric/epoxy-matrix composites was studied in this paper. The experimental results shows that impact can cause damage in composites, degenerate compressive intensity, and increase resistance. The electrical resistance change rate was used as an evaluation indicator of impact damage tolerance of composites. Impact damage, which results from the applying process of composites, can be identified in time by electrical resistance measurement. So, the safety performance of composites can also be improved.

Effects of electrical resistance on the spontaneous combustion tendency of coal and the interaction matrix concept

There have been several developments in determining the spontaneous combustion liability of coal. Most of the methods of concern have purely been based on the internal properties of the coal itself. The relation between the crossing-point method and the electrical resistance of coal was examined here to outline the spontaneous combustion tendency of coal, The electrical resistance property of coal was looked into as a decision-making parameter of the interaction matrix concept for the final decision on the spontaneous combustion tendency.

Detecting the Resistivity Distribution of Carbon Fiber Reinforced Concrete by Electrical Resistance Tomography Method

According to the principle of electrical resistance tomography （ ERT）, the resistivity distribution of the carbon fiber reinforced concrete （CFRC） in the sensing field can be measured by injecting exciting current and measuring the voltage on the sensor electrode arrays installed on the surface of the object. Therefore, measurement of the resistivity distribution of CFRC is divided into first measuring the boundary conditions and then inversely computing the resistivity distribution. To reach this goal, an ERT system was constructed, which is composed of a sensor array unit, a data acquisition unit and an image reconstruction unit. Simulations of static ERT was performed on set-ups with many objects spread in a homogeneous background, and a simulation of dynamic ERT was also done on a rectangular board, the resistivity of which was changed within a small domain of it. Then, the resistivity distribution of a CFRC sample with a circlar hole as the target was detected by the ERT system. Simulation and experimental results show that the reconstructed ERT image reflects the resistivity distribution or the resistivity change of CFRC structure well. Especially, a small change in resistivity can be identified from the reconstructed images in the simulation of dynamic ERT images.

Effects of Home Laundering on Electrical Resistance of Signal Transmission Lines on Colored E-Textiles

The aim of this work was to investigate the electrical resistance change of electro-textiles manufactured using cotton fabrics with stainless steel and silver plated PA yarns incorporation after being subjected to home laundering, i.e. detergent washing and silicone softening. Electrical resistances of conductive yams inside the fabric structure were compared and discussed statistically before and after washing and softener application. Greatest changes in electrical resistances were observed with samples including silver plated PA yams. After five washing cycles with detergent, silicone softening agent is removed from yarns by washing, and thus conductivity increases. Further washing of e-textiles with detergent for five more cycles causes decrease in conductivity, because of chemical effects of detergent and mechanical effects of washing process such as abrasion due to friction. Detergent which has negative reactive sites bonds with metal ions reduces conductivity.

Exploration on electrical resistance tomography in characterizing the slurry spatial distribution in cemented granular materials

This study investigated the application of electrical resistance tomography(ERT)in characterizing the slurry spatial distribution in cemented granular materials(CGMs).For CGM formed by self-flow grouting,the voids in the accumulation are only partially filled and the bond strength is often limited,which results in difficulty in obtaining in situ samples for quality evaluation.Therefore,it is usually infeasible to evaluate the grouting effect or monitor the slurry spatial distribution by a mechanical method.In this research,the process of grouting cement paste into high alumina ceramic beads(HACB)accumulation is reliably monitored with ERT.It shows that ERT results can be used to calculate the cement paste volume in the HACB accumulation,based on calibrating the saturation exponent n in Archie’s law.The results support the feasibility of ERT as an imaging tool in CGM characterization and may provide guidance for engineering applications in the future.

Accurate electrical resistance measurement of the crystallization kinetics of amorphous alloys

An accurate four-line ac electrical resistance measurement (ERM)apparatus was developed. By using the ERM the crystallization kinetics of amorphous Ni80P20, FeZr2, Fe86B14 alloys were investigated. The experimental results show that the ERM can identify the early stage of crystallization in amorphous alloys. The ERM detects a crystallization temperature range obviously wider than the DSC does, indicating that the ERM is more sensitive to the structure evolution in crystallization. For the eutectic or polymorphic crystallization, three distinct processes can be identified from the measured resistance variation: (i) crystal nucleation, (ii) subsequent growth of crystal nuclei, and (iii) coarsening of the crystallites. In the early stage of the primary crystallization, the ERM results reflect the nucleation information as well.