Eddy Current Testing of Metallic Materials Using Projection Methods

Using the example of nonmagnetic metallic materials, the projection methods of multidimensional analysis of multifrequency eddy-current testing measurement data presented for processing are considered. Based on the principal components method, the effects of electrical conductivity and sensor–material-surface gap on the results of testing have been separated. Using regression on principal components, the numerical values of the electrical conductivity and gap for manganese, copper, bronze, aluminum, and an aluminum alloy have been obtained. The results make it possible to extend the possibilities of nondestructive eddy-current evaluation of materials.     

A thermal porosimetry method to estimate pore size distribution in highly porous insulating materials

Standard pore size determination methods such as mercury porosimetry, nitrogen sorption, microscopy, or x-ray tomography are not always applicable to highly porous, low density, and thus very fragile materials. For this kind of materials, a method based on thermal characterization is proposed. Indeed, the thermal conductivity of a highly porous and insulating medium is significantly dependent on the thermal conductivity of the interstitial gas that depends on both gas pressure and size of the considered pore (Knudsen effect). It is also possible to link the pore size with the thermal conductivity of the medium. Thermal conductivity measurements are realized on specimens placed in an enclosure where the air pressure is successively set to different values varying from 10(-1) to 10(5) Pa. Knowing the global porosity ratio, an effective thermal conductivity model for a two-phase air-solid material based on a combined serial-parallel model is established. Pore size distribution can be identified by minimizing the sum of the quadratic differences between measured values and modeled ones. The results of the estimation process are the volume fractions of the chosen ranges of pore size. In order to validate the method, measurements done on insulating materials are presented. The results are discussed and show that pore size distribution estimated by the proposed method is coherent.     

探头引线热损失对TPS法测量导热系数的影响

瞬态平面热源(Transient plane source,TPS)法是一种近年来发展起来的用于测量材料导热系数的方法.在测量过程中,加热功率受到探头引线传热的影响,进而会影响导热系数的测量准确度.针对这个问题,本文研究了测量过程中探头引线热损失对加热功率的影响,推导了热损失的数学计算公式,并提出了相应的修正模型.利用hot disk热常数分析仪对不同材料进行了一系列测量实验.实验结果表明引线热损失对测量的影响随着测量材料以及测试探头尺寸的不同而发生变化.当材料的导热系数大于0.2 W/(m·K)时,探头引线热损失的影响小于0.16％,可以忽略不计;但对于低导热系数材料的测量,对引线热损失进行补偿可以有效地提高导热系数的测量准确度.     

Flexible contact stamp for electrical conductivity measurements of a soft matter

In this communication, a simple homemade four probe conductivity setup has been presented to measure the electrical conductivity of molecularly grafted and passivated solid surfaces. Setup was also extended for the temperature dependent conductivity measurements by designing a small furnace using nichrome heating element. The importance of prepared setup lies in its easy designing ability, portability and reliability to measure the conductivity of soft matters. Setup was designed for four probe conductivity measurements which can be used for two probes conductivity measurements also, depending upon the requirements under investigation. Setup was tested using its four probes for electrochemically grafted indium tin oxide surfaces with thiol containing organic molecules and trichloroethylene passivated Si surface. It was found very sensitive even for observing small changes in current–voltage values whereas recorded curves were quite reproducible.     

Effect of friction stir processing parameters on the microstructural and electrical properties of copper

Friction stir processing (FSP) is an innovative technology, based on friction stir welding (FSW) operative principles, which can be used for changing locally the microstructure and the mechanical properties of conventional materials. In this work, the copper alloy C12200 was friction stir processed using two distinct tools, i.e. a scrolled and a conical shoulder tool, in order to promote different thermomechanical conditions inside the stirred volume, and consequently, varied post-processed microstructures. The influence of the tool geometry and tool rotation and traverse speeds on the microstructural and electrical properties of the processed copper alloy was analysed. The processing conditions were found to have an important influence on the electrical conductivity of the processed material. The differences in electrical conductivity were explained based on dislocations density effects. The effect of the dislocations density on electrical conductivity of the processed material was found to prevail over the effect of the grain boundaries.     

引进合金钢标准物质复验

简单介绍了对引进国外合金钢标准物质分析复验情况,合金铜标准物质复验分析中使用的仪器和方法。对于适合微量元素钼、钴和铜的分析方法进行了研究。与国内标准物质进行了比较,经不同人员、不同方法、不同仪器验证,其均匀性、稳定性好,定值准确,各元素覆盖范围宽,可以作为标准物质使用,使用过程中必须定期复验。通过本文的总结,使大家对合金钢标样的国内外现状有更清晰的认识,更准确地应用国外的标准物质。     

铜石墨材料导电性能研究

以镀铜石墨粉为原料，用压制－烧结的工艺制备了不同铜含量的铜石墨材料，研究其电导率随铜含量变化的规律，并与传统的铜石墨材料的导电能力进行比较。研究发现，用镀铜石墨粉制备的铜石墨材料的电导率与铜体积分数呈简单线性关系，拟合曲线外推到铜体积分数为100％时与纯铜电导率相近，说明铜的导电能力几乎得到充分发挥。含铜量为75％的镀铜石墨试样的导电性能优于含铜量为85％的传统铜石墨材料。     

Direct electrodynamic electromagnetic-acoustic transformation in a normal polarizing field: III. Dependence of the acoustic field on macroscopic parameters of transformation medium

Frequency dependences of shear displacements in solids with different conductivities are numerically calculated on the basis of exact analytical expressions for projections of elastic displacements in a solid. It is shown that shear displacements in well-conducting materials at not too high quasistationary frequencies are independent of the electrical conductivity. This is determined by both the skin effect and the fact that the main agent responsible for transferring the energy of a source-generated quasi-stationary field is its magnetic component. In relatively weakly conducting materials, displacements may be proportional to the electrical conductivity. For well-conducting materials, a good approximation containing no integrals and allowing determination of both the transformation efficiency and angle of injection of elastic vibrations near the radiation-stabilization point is obtained.     

The measurement of thermal conductivity variation with temperature for solid materials

An apparatus was designed to routinely measure the thermal conductivity variation with temperature for solid materials. The apparatus was calibrated by measuring the thermal conductivity variations with temperature for aluminum, zinc, tin and indium metals. The variations of thermal conductivity with temperature for the Zn-[x] wt.% Sb alloys (x = 10, 20, 30 and 40) were then measured by using the linear heat flow apparatus designed in present work. From experimental results it can be concluded that the linear heat flow apparatus can be used to measure thermal conductivity variation with temperature for multi component metallic alloys as well as pure metallic materials and for any kind of alloys. Variations of electrical conductivity with temperature for the Zn-[x] wt.% Sb alloys were determined from the Wiedemann–Franz (W–F) equation by using the measured values of thermal conductivity. Dependencies of the thermal and electrical conductivities on composition of Sb in the Zn–Sb alloys were also investigated. According to present experimental results, the thermal conductivity and electrical conductivity for the Zn-[x] wt.% Sb alloys decrease with increasing the temperature and the composition of Sb.     

ITS Reconstruction Tool-Suite: An inverse algorithm package for industrial process tomography

Electrical resistance tomography (ERT) and electrical capacitance tomography (ECT) are two established process tomography techniques that can be applied into various indsutries. ERT can monitor the electrical conductivity changes in the process whereas ECT can detect the electrical dielectric materials. Due to their high-speed and low cost features, they are particularly attractive to industrial applications which require real time conditional monitoring. For the past decades, 2D linear back projection (LBP) has been the standard technique for both commercialised ERT and ECT systems because of its simplicity and fast reconstruction speed. In this paper, ITS Plc has released a 'Reconstruction Tool-Suite' software that allows industrial users to utilise different reconstruction algorithms to further understand their processes. Different algorithms are integrated into this software package including the single step Tikhonov method and the iterative Landweber method. In the latest version of the software, the full-field 3D tomography reconstruction scheme is also included, which allows the users to perform 3D reconstruction for their processes. A series of experiments are conducted to validate the pros and cons of different methods.     

陶瓷电主轴空载电磁振动试验的研究

近年来,对高速高刚度数控机床用电主轴的需求日益紧迫。采用陶瓷材料设计电主轴主要旋转部件可以提高电主轴极限转速及刚度。但由于陶瓷材料导热、导磁及导电及机械性能与金属材料差别较大,因此陶瓷电主轴电磁振动与金属电主轴有所不同。研究陶瓷电主轴电磁振动有利于实现电主轴的低噪声低振动优化设计。本文通过实验研究了陶瓷电主轴的电磁振动特性。     

Substrate properties affect the mass loss rate in collodion at liquid helium temperature

A previous measurement showed that mass loss from collodion supported by thin carbon films was linear with electron exposure at liquid helium temperature. No other organic solid had shown a linear loss of mass at any temperature. When measurements of collodion were done using titanium supports, the loss of mass proceeded exponentially with exposure at liquid helium temperature. This result suggested that the differing electrical conductivities of these substrates might be the cause of the different mass loss effects. Carbon films, which are typically used at ambient temperatures, have much lower electrical conductivity at very low temperature than titanium films. This suggested that specimen preparation materials and techniques used routinely for room temperature studies may need to be modified when microscopy is done using superconducting objective lenses. For both substrates, the rate of mass loss is slowest at liquid helium temperature.     

Minimization of focused ion beam damage in nanostructured polymer thin films

Focused ion beam (FIB) instruments have proven to be an invaluable tool for transmission electron microscopy (TEM) sample preparation. FIBs enable relatively easy and site-specific cross-sectioning of different classes of materials. However, damage mechanisms due to ion bombardment and possible beam heating effects in materials limit the usefulness of FIBs. Materials with adequate heat conductivity do not suffer from beam heating during FIB preparation, and artifacts in materials such as metals and ceramics are primarily limited to defect generation and Ga implantation. However, in materials such as polymers or biological structures, where heat conductivity is low, beam heating can also be a problem. In order to examine FIB damage in polymers we have undertaken a systematic study by exposing sections of a PS-b-PMMA block copolymer to the ion beam at varying beam currents and sample temperatures. The sections were then examined by TEM and scanning electron microscopy (SEM) and analyzed using electron energy loss spectroscopy (EELS). Our empirical results show beam heating in polymers due to FIB preparation can be limited by maintaining a low beam current (≤100 pA) during milling.     

Development of Optimum Electrodischarge Machining Technology for Advanced Ceramics

In recent years, ceramic materials with improved properties have been developed to meet a large number of industrial applications. However, in most cases, the cost of the ceramic components is very high. On some occasions, the final machining of the component (especially if complex geometries are to be obtained) accounts for an important percentage of the final cost. The electrodischarge machining process can be a good choice if the material has at least a minimum electrical conductivity, since it can produce very complex shapes and it is not dependent on the hardness or abrasiveness of the material itself. In this paper, the development of sinking and wire electrodischarge machining technology for two ceramics with a promising future (boron carbide and silicon infiltrated silicon carbide) is described. The high removal rates, as well as the possibility of obtaining an excellent surface finish, prove the feasibility of the industrial application of this production method.     

基于氧化石墨烯的阻变存储器制备

阻变存储器是一种新型非易失性存储器,其在外加电场作用下可实现高阻态和低阻态之间的切换。存储器电极材料和活性层材料的选择及相互作用是实现器件阻变特性的主要因素。石墨烯是具有优良导电性和高延展性的二维材料,通过激光加工还原氧化石墨烯是高效获取石墨烯的极佳方法。传统存储器的制备过程复杂,不利于大规模加工制造。以金属金（Au）和还原氧化石墨烯（rGO）作为电极,氧化石墨烯（GO）作为阻变层进行器件制备,很好地实现了存储器的阻变功能。简单高效的制备方式为大规模、高集成化生产阻变存储器提供了参考。     

Synergetic effect of BN for the electrical conductivity of CNT/PAN composite fiber

Carbon nanotube (CNT) fillers in composite materials improve electrical conductivity, thermal stability, and mechanical properties. Boron nitride (BN) is an insulating material that is also thermally stable. Therefore, CNT and hexagonal boron nitride (hBN) fillers have been used to obtain composite materials’ high electrical conductivity. In this study, CNT-hBN/polyacrylonitrile (PAN) fibers were spun using simple wet-spinning and the effect of hBN on the electrical conductivity of the CNT-hBN/PAN composite was investigated. Contrary to predictions, as the content of the insulating material, BN, increased up to 15 wt%, the electrical resistance of the composite fiber decreased.

     

Some aspects of optimizing contrasts for the investigation of joint materials in the environmental scanning electron microscope

In the environmental scanning electron microscope, material joints of different atomic mass and different electrical conducting properties can easily be observed simultaneously without coating the specimen. For such heterogeneous materials, the quality of the image can be optimized with respect to contrast and resolution if the contrast types as well as their significance to the composition of the image are known.     

An adaptive Tikhonov regularization parameter choice method for electrical resistance tomography

Electrical resistance tomography (ERT) reconstructs the conductivity distribution from the boundary changes of electrical measurements. The inverse problem of ERT is seriously ill-posed where regularization methods are needed to treat this ill-posedness. A proper choice of regularization parameter which controls the degree of smoothing is very important for these regularization methods. Although have been a variety of methods, such as L-curve method, to choose a reasonable parameter for the problem, these methods usually result in a scalar parameter which cannot distinctly express the spatial characteristic of the conductivity distribution. So a spatially adaptive regularization parameter choice method is proposed for regularizing the inverse problem of ERT based on Tikhonov regularization. Since large regularization parameters can stabilize and smoothen the solution, while small regularization parameters can approximate and sharpen the solution, the proposed method adaptively updates the regularization parameters during the iteration process and provides spatially varying parameter for each pixel of the reconstructed image. When the iteration is stopped, large regularization parameters for the smooth background region and small regularization parameters for the object region can be obtained. The method is discussed using simulated data for some typical conductivity distributions, and further applied to the analysis of real measurement data acquiring from the practical system. The results demonstrate that flexible regularization parameter vectors can be achieved for different distributions and the strength of regularization is adaptively provided for different regions in a specific distribution. The adaptive method achieves an efficient and reliable regularization solution and has outstanding performance in noise immunity especially in smooth background regions.     

添加少量纳米SiCp对铜基材料电学和摩擦学性能的影响

考察了添加少量纳米SiCp对铜基材料电学和摩擦学性能的影响。结果表明：添加少量纳米SiCp(体积分数为0．5％),轻微降低了铜基材料的导电率,显著提高了耐磨性,有效降低了铜／钢摩擦副之间的粘着作用和材料转移;130nm SiCp／Cu基复合材料的导电性和耐磨性都优于30nm SiCp／Cu基复合材料。     

Resonant torsional apparatus for contactless measurements of electrical conductivity and magnetic susceptibility of solids

We have constructed a torsional resonance apparatus for contact-free measurements of the electrical conductivity of solids. Owing to its use of modulation spectroscopy, the technique achieves considerable enhancement of sensitivity compared to previous contactless methods. Conductivities in the range 10(-5) mho/cm to 10(-6) mho/cm can now be measured by the contactless technique. Measurements of magnetic susceptibility as low as 10(-12) can be made. This sensitivity allows for investigation of magnetic impurities as dilute as 1 part in 10(7). In samples which display both phenomena of electrical conductivity and magnetic susceptibility, the two effects can be sorted out via analysis of frequency and/or temperature dependence. The present apparatus has potential for considerable improvement.