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.

Improvement of Boxcar Integrator and Its Application to Low Resistance Measurement of Inductive Load Coil

A boxcar integrator is described which is suitable for the low-repetition-rate signal processing. This boxcar integrator, named fixed-interval mode boxcar integrator, is able to reject harmonics other than the first harmonic component. It can also decrease the effective time constant In many situations, the antialiasing filter with narrow bandwidth will cause distortion of the input signal. The fixed-interval mode boxcar integrator with suitable gate width can achieve relative high performance without signal distortion because the bandwidth of its antialiasing filter can be wider than that in the fixed-Point boxcar integrator. ms boxcar integrator is used as majn part of signalprocessing circult in the low resisance measurement of inductive load coil. The results of experiments show that the fixed-interval boxcar integrator is suitable for low-repetition-rate use.

ELECTRIC RESISTANCE MEASUREMENT OF CARBON FIBRE SMART CONCRETE

After having measured the electric resistance of carbon firbre reinforced concrete (CFRC) by applying a D. C. current, it was found that the current passing through the specimen under a constant voltage decreased with the time, and if changing the value of voltage, the electric resistance was obviously affected. When current flew through the specimen, polarisation emerged under a high votage (>5 upsilon), but that could be neglected under a low voltage (<5 upsilon).(1)

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.

Automated dual source systems for measurement of DC resistance standards

A new system for measuring low-ohmic standard resistors through a dual current sources bridge is introduced.It is used for low resistance measurements from 1 mΩto 1Ωat 1∶1 ratio,which is suitable for the laboratories without cryogenic current comparators(CCC)or direct current comparators(DCC)bridges.Behavior of this bridge is evaluated by comparing its measured values with the unknown resistor values obtained by another method.The accuracy of the introduced bridge is in the level of 10-5 for the 1 mΩresistor,and in the level of 10-4 for the 10 mΩ,100 mΩand 1Ωresistors.Moreover,a dual voltage sources system for the measurement of DC standard resistors from 1 kΩto 100 MΩis also presented.In this system,a modification is made on the modified Wheatstone bridge to evaluate its performance by adding another digital multimeter to measure the ratio between the unknown and the standard resistors simultaneously.This bridge is verified by comparing the measured values of 10 kΩresistor obtained by the two methods with its actual value.The bridge accuracy is in the level of 10-6 except for the 1 kΩresistor,and the bridge asymmetry is also evaluated.It is found the asymmetry is in the level of 10-6 for the resistors from 10 kΩto 100 MΩand in the level of 10-5 for 1 kΩresistors.The introduced bridges operations are controlled by LabVIEW programs designed specially for this purpose,and the expanded uncertainty is also evaluated for all measurement results.

STUDY ON TESTING TECHNIQUE FOR MEASUREMENT OF FATIGUE－CREEP INTERACTION RESISTANCE

By using dropped stress creep method a new testing technique for measurement of the fa-tigue-creep interaction resistance is developed. At varied adjusted mean stresses the creep testingwas performed repeatedly When an unlimited extensive incubation period with zero creep rate oc-curred. the stress cavsing zero creep rate is defined as fatigue-creep resistance. The developped test-ing technique was used to measure the fatigue-creep resistance in F anc C regions. The dynamic ef-fective stress could yield a better descrption of fatigue and creep interaction. The fatigue-creep rateequations with varied exponents inF of C region are established. The different deformation mecha-nisms in F or C regions are indicated

Analysis of the Correlation between the Level of Contact Degradation and the Dynamic Resistance Curve in Circuit Breakers

The DRM （dynamic contact resistance measurement） in high voltage circuit breakers is a manner of evaluating the internal ageing condition of the chamber. DRM is similar to static contact resistance measurement testing, but instead of measuring a single value when the breaker contacts are closed （static value）, the ohmic resistance is measured at various contact positions, from the beginning of the contact opening until a complete separation of the contacts. The relationship between the contact resistances of the new circuit breaker and the ageing circuit breaker in operation provides subsidy for the evaluation of both the main and arcing contact conditions. This research aims to analyze the correlation between the various levels of degradation of the contacts and the configuration of the DRM curve. This work considers curve samples from new acceleration tests. breaker chamber contacts and different levels of degradation by

Measurement of thickness and heat transfer coefficient of water film out of tube in an evaporative air cooler

Thickness of falling water film out of tubes is one of critical factors of heat transfer of evaporative air cooler. A new method of resistance measurement was developed to measure thickness of the film. When the resistance probe on the tip of micrometer touches the surface and bottom of the film, two corresponding sudden reductions of resistance occurs, and the difference of two graduations on the micrometer displays the thickness of the film. The film thickness of eleven angles was measured in five kinds of water flows and results varies from 0.8933mm to 1.7233 mm. Mean thickness and mean heat transfer coefficient of the film out of the tube was calculated.

Design of TE_(01δ) Test Probe for Measuring the Microwave Surface Resistance of HTS Thin Film

A new TEo1δ test probe with proper transmission factor is fabricated for the measurement of surface resistance of high temperature superconductor （HTS） thin film. Coupling holes instead of coupling loops are used in the probe for its easier machining and relatively low loss. Two 6 mm × 3 mm × 8 mm dielectric waveguides, one side of them is coated by silver, are used for coupling. The measurement result of S21 agrees well with the simulation because the size of the probe can be rigidly controlled by machine. The microwave surface resistance of four YBCO/MgO films are measured at 77 K and 12 GHz and scaled to 10 GHz according to thef2 rule. The average surface resistance of four HTS thin fdms is 0.38 mΩ, the standard deviation and relative standard deviation of one single HTS thin film are 0.009 mΩ and 2.4%, respectively.

Detection performance and inversion processing of logging-while-drilling extra-deep azimuthal resistivity measurements

We present systematic investigations on the physics,detection performance and inversion of logging-while-drilling extradeep azimuthal resistivity measurements(EDARM).First,the definitions of EDRAM measurements are discussed,followed by the derivation of the attenuation and phase-shift geometrical factors to illustrate the relative contributions of formation units to the observed signals.Then,a new definition of detection depth,which considers the uncertainty of inversion results caused by the data noise,is proposed to quantify the detection capability of ED ARM.Finally,the B ayesian theory associated with Markov chain Monte Carlo sampling is introduced for fast processing of EDARM data.Numerical results show that ED ARM is capable of detecting the azimuth and distance of remote bed boundaries,and the detection capability increases with increasing spacing and resistivity contrast.The EDARM tool can accommodate a large range of formation resistivity and is able to provide the resistivity anisotropy at arbitrary relative dipping angles.In addition,multiple bed boundaries and reservoir images near the borehole are readily obtained by using the Bayesian inversion.

Resistivity measurement of conductive asphalt concrete based on two-electrode method

The objective of this work is to develop a novel methodology for determining real resistivity of conductive asphalt concrete based on two-electrode method.Due to an influence of contact resistance,the measured resistivity is always not equal to the real resistivity.To determine the real resistivity,a linear relationship of the measured resistivity,contact resistance and the real resistivity was established.Then experiments for six specimens with varying graphite contents were designed and performed to validate the formulation.Results of experiments demonstrate that the slope of the line represents contact resistance,and the intercept indicates the real resistivity.The effects of graphite content on contact resistance and real resistivity are also revealed.Finally,results show that the influence of contact resistance on accuracy of resisitvity measurement becomes more serious if graphite content is beyond 3%.Hence,it is the time to choose this novel methodology to determine the real resistivity of asphalt concrete by taking account of contact resistance.

Enhancing Accuracy of Flexible Piezoresistive Pressure Sensors by Suppressing Seebeck Effect

Flexible piezoresistive pressure sensors can offer convenient detection of mechanical deformations for wearable electronics.Previous studies of flexible piezoresistive pressure sensors focus on the sensitivity but the low-cost and self-powered sensors remain a challenge due to the deviation of resistance signal acquisition caused by thermoelectric voltage.Here,piezoresistive pressure sensors with ultralow Seebeck coefficient of-0.72μV/K based on carbon nanotubes(CNTs)/polyethyleneimine(PEI)/melamine(CPM)sponge are reported.Due to the diminished Seebeck effect,the CPM sponge pressure sensors successfully reduce the deviation to 18.75%and can keep stable sensitivity and resistance change under a very low working voltage and change temperature environment.The stable properties of the sensors make them successful to work for real-time sensing in self-powered wearable electronics.

Calculation of skid resistance from texture measurements

There is a wide range of routine skid resistance measurement devices on the market. All of them are measuring the friction force between a rubber wheel and the wetted road surface. Common to all of them is that they are relatively complex and costly because generally a truck carrying a large water tank is needed to wet the surface with a defined water layer. Because of the limited amount of water they can carry they are limited in range. Besides that the measurement is depending on factors like water film thickness, temperature, measurement speed, rubber aging, rubber wear and even road evenness and curviness. All of these factors will affect the skid resistance and are difficult to control. We present a concept of contactless skid resistance measurement which is based on optical texture measurement and consists of two components： measurement of the pavement texture by means of an optical measufin~ system and calculation of the skid resistance based on the measured texture by means of a rubber friction model. The basic assumptions underlying the theoretical approach and the model itself based on the theory of Persson are presented. The concept is applied to a laboratory device called Wehner/Schulze （W/S） machine to prove the theoretical approach. The results are very promising. A strong indication could be provided that skid resistance could be measured without contact in the future.

Magnetotelluric study of the Xuefeng mountain area,Hu'nan Province,China

A magnetotelluric study was carried out in the Xuefeng mountain uplift belt and its western margins. A detailed investigation was made of the resistivity of the formations, and reliable data were obtained. The sedimentary cover and basement structure of the Xuefeng mountain area and the deep geological structure were analyzed in detail using magnetotelluric data from the twodimensional inversion of the resistivity profile data in combination with regional gravity and magnetic data. It was concluded that the tectonic movements were characterized by basement detachment, and north-south ramp.The study area can be divided into a southern uplift zone, a southern thrust-faulted zone, a central uplift zone, and a northern depression zone. This work has provided geophysical evidence that can be used in future studies of the tectonics and petroleum geology of this region.

Failure mechanism of Mesozoic soft rock roadway in Shajihai coal mine and its surrounding rock control

In view of the buckling failure caused by large deformation of Mesozoic soft rock roadway in Shajihai mining area, such as serious roof fall, rib spalling, floor heave, etc., based on the detail site investigation,theoretical analysis, mineral composition test, microstructure test, water-physical property test and field experiments were carried out. And we revealed the compound failure mechanism of Mesozoic soft rock roadway in Shajihai mining area, namely the molecule expansion-shear slip of weak structural plane-construction disturbance. On this basis, the coupling support technology whose core is constant resistance with large deformation bolt was proposed. The feature of this supporting technology is that a new type of structural composite material was used, which makes the supporting system not only has the ideal deformation characteristics, but also has high supporting resistance. Thus the fully release of plastic energy within surrounding rock and reasonable control of the thickness of the plastic ring were realized. Then the differential deformation between the surrounding rock and support was eliminated by the secondary coupling support of bolt–mesh–cable, and the bolt with high strength was applied in the base angle to control floor. Eventually the collaborative bearing system of surrounding rock–support was formed. Through field tests the validity and rationality of support was also verified.

Tectonic activity and earthquake risk in the Chengnanhe fault zone in Weihai city,Shandong province,China,obtained by using an integrated prospecting technique in geophysics and geology

For city planning and reducing potential earthquake risk,it’s necessary to detect the information of the buried faults in an urban area especially,including the location and activities.An integrated technique with geophysical and geological methods,including the shallow seismic reflection profile,electrical resistivity measurement,geologic borehole section,and exploration trench,was used to detect the Chengnanhe fault,which is one of the two main faults passing through the Weihai urban area in Shandong province,China.The results show that it is a normal fault striking with E-W direction,and it is relatively inactive and stable.By using the thermoluminescence(TL)dating,we found that the Chengnanhe fault initiated in mid-Pleistocene and there was no offset after late Pleistocene.Such an integrated technique with multiple geological and geophysical methods provides a significant assessment of earthquake risk for city planning in urban areas.

New High Tc-Value Investigated in Superconducting System YBa2（C u3）1-xA gxO6.5x＋δ

A ceramic superconductor compound with composition YBa2（C u3）1-xA gxO6.5x＋δhas been prepared experimentally by solid state reaction from principal roots of high purity materials like Y203, BaO, CuO and Ag20. The study was concentrated on the effect of partial substitution of Ag with respect to Cu atoms by the ratios （x = 0, 1, 0.2, 0.3, 0.4 and 0.5） through different analysis and measurements. X-ray diffraction （XRD）, Scanning Electron Microscope （SEM） and Resistivity measurement is play an important role to show the improvement on high superconducting phase. It was found that the best substituted value of （x = 0.5） investigated a favor value of Tc equal nearly to （123 K）, due to more excess of Ag atoms in the structure. X-ray diffraction showed an orthorhombic structure related to high-To phase with high stability through diminishing some peaks related to low temperature superconducting phase, that was related to presence of multiphase derivative from YBCO-phase. SEM pictures give us more details on the surface morphology, grain and grain boundaries, it gives an indication on successful of sintering process, the last one is very important in forming superconducting phase.

Neurocomputing van der Pauw function for the measurement of a semiconductor's resistivity without use of the learning rate of weight vector regulation

Van der Pauw＇s function is often used in the measurement of a semiconductor＇s resistivity. However, it is difficult to obtain its value from voltage measurements because it has an implicit form. If it can be expressed as a polynomial, a semiconductor＇s resistivity can be obtained from such measurements. Normally, five orders of the abscissa can provide sufficient precision during the expression of any non-linear function. Therefore, the key is to determine the coefficients of the polynomial. By taking five coefficients as weights to construct a neuronetwork, neurocomputing has been used to solve this problem. Finally, the polynomial expression for van der Pauw＇s function is obtained.

Evaluation method of rock damage under uniaxial compression based on unit series-parallel electrical conductive model

The evaluation of rock damage behaviour is an important requirement for ensuring stability control and safety prediction in rock engineering.However,they have not been able to obtain sufficiently accurate and dynamic results due to the insufficient evaluation method.In this study,by means of fractals and unit series division,a unit series-parallel conductive model of damaged rock is derived,and a new evaluation method of rock damage under uniaxial compression was proposed.Rock was damaged by uniaxial compression,while electrical measurements and X-ray microscopy tests were performed to obtain the damaged rock resistivity,porosity,and fractal dimension variation.By establishing the relationship between defined meso-damage factor and resistivity,rock damage evolution law under axial compression was obtained.The results indicate that the growth trend was agree with the classical statistical damage model,which verified the accuracy of the results obtained by the proposed method.Moreover,as the strain increased,the damage factor determined by resistivity gradually decreased to0.06 firstly and then increased rapidly to 0.79.Different from previous damage evolution law,brittle failure was observed and the cracks development in each stage was considered,including the closure(negative damage)and expansion(positive damage)of cracks.

Thermal analysis in high power GaAs-based laser diodes

The thermal characteristics of 808 nm Al Ga As/Ga As laser diodes（LDs） are analyzed via electrical transient measurements and infrared thermography. The temperature rise and thermal resistance are measured at various input currents and powers. From the electrical transient measurements, it is found that there is a significant reduction in thermal resistance with increasing power because of the device power conversion efficiency. The component thermal resistance that was obtained from the structure function showed that the total thermal resistance is mainly composed of the thermal resistance of the sub-mount rather than that of the LD chip, and the thermal resistance of the sub-mount decreases with increasing current. The temperature rise values are also measured by infrared thermography and are calibrated based on a reference image, with results that are lower than those determined by electrical transient measurements. The difference in the results is caused by the limited spatial resolution of the measurements and by the signal being captured from the facet rather than from the junction of the laser diode.