VE-26NP Eddy-Current Structuroscope

The destination and technical characteristics of a VE-26NP eddy-current structuroscope are described. The domains of application and characteristics of the VE-26NP eddy-current structuroscope are presented. The question of the necessity for presorting on the basis of the specific electrical conductivity is considered. The possibilities of using the VE-26NP eddy-current structuroscope for nondestructive testing of the quality of heat treatment of products from nonmagnetic alloys are analyzed. Examples of testing the specific electrical conductivity of thin-wall objects are given.     

Eddy-current quality control of soldering of current-carrying joints in electrical machines. I. General principles

The possibility of testing the electrical conductivity of soldered joints using and eddy-current transducer has been studied. The simplest model calculations allowing evaluation of the relative value of a signal from an inhomogeneity depending on its location inside a specimen are presented. It is shown that signals yielded by an eddy-current transducer are quite informative for determining the quality of soldering of current-carrying joints.     

On the choice of the optimal algorithm for the processing of infrared thermograms in active thermal testing

A comparative study of the effectiveness of algorithms for processing infrared images, namely, Fourier and wavelet analysis, analysis of principal components, polynomial fitting, and other types, has been performed with active thermal testing of metals and nonmetals and using optical, convective, ultrasonic, and eddy-current stimulation.     

Experience in eddy-current testing of mounting holes in aircraft components

Opportunities offered by the static and dynamic eddy-current techniques for testing mounting holes in aircraft components fabricated from nonmagnetic materials and features of these techniques are considered. Examples of applications of eddy-current techniques demonstrating considerable advantages of the dynamic technique in detection of cracks around holes are given.     

Application of principal component analysis in dynamic thermal testing data processing

The principles and features of the application of statistical principal component analysis (PCA) in active thermal testing are considered. A comparison between PCA and Fourier analysis in finding defects in composite materials, detecting corrosion in aluminum, and determining moisture content in construction materials is performed. It is concluded that, generally, images of principal components increase the signal-to-noise ratio and are close in performance to phase diagrams; nevertheless, the results of this method are poorly predictable and require further analysis.     

A Finite-element modeling of a probe of eddy-current quality testing of soldered joints in turbogenerator windings

The problems of the modeling and calculation of the screen probe for eddy-current testing of soldered joints in the stator windings of turbogenerators according to the finite-element method are considered. The choice of an informative parameter is rationalized and the effects of interfering parameters are studied; the principal characteristics of the designed probe and results of their testing on real objects are given.     

Nondestructive testing of mechanical characteristics of aluminum alloys on the basis of their electrical conductivity

The results of studies of the interrelations between the mechanical characteristics of aluminum alloys applied in rocket and spacecraft engineering and electrical conductivity are presented. The conductivity was measured with a BЭ-26H instrument. The requirements for upgrading the conductivity-measuring device aimed at a further development of the methods for testing of the mechanical characteristics are formulated.     

Evaluating Specific Electrical Conductivity of Two-Layered Nonmagnetic Objects by Pulsed Eddy-Current Method

Russian Journal of Nondestructive Testing - Evaluating the specific electrical conductivity of two-layered nonmagnetic objects by the pulsed eddy-current method is considered. Eddy-current...     

Mathematical model of a double-coil inductive transducer for measuring electrical conductivity

A technique for the contactless measurement of the electrical conductivity of conducting materials using a double-coil inductive transducer is presented. A mathematical model of the transducer has been created and it consists of two cylindrical coils and a tested sample in the form of a cylinder coaxial with the coils. A processing function of the transducer is defined as the ratio of voltages between terminals of the measurement coil with and without the test sample. This processing function depends on the conductivity of the test sample, the dimensions of the sample and of both coils of the transducer (the measurement coil and the excitation coil), and the frequency of the current supplied to the excitation coil. An analytical formula for the processing function is derived; analysis of graphs of this function in different formats enables us to evaluate the influence of all the essential parameters of the transducer. This is a necessary step for both transducer optimization and carrying out of the conductivity measurement of the investigated materials. In order to verify the theoretical predictions, experimental investigations have been performed using a computerized data acquisition system. First, an experimental validation of the obtained analytical formula has been completed using an aluminum sample of known conductivity. Then, the conductivity measurements of a sample made of brass have been carried out. The obtained experimental results confirm the high accuracy of the theoretical analysis.     

Eddy-current nondestructive testing of long cylindrical components using spatial magnetic field components of different frequencies

The feasibility of the eddy-current nondestructive testing using two orthogonal harmonic components of the driving magnetic field has been studied. The paper describes the practical implementation of the method in a flaw detector testing ferromagnetic rods and pipes and designed for detecting elongated flaws with small gradients of longitudinal parameters.     

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.     

Afterpulses in a proportional counter with various cathode materials

The results of an investigation of afterpulses arising in a proportional counter due to the photoeffect on the cathode are presented. It was found that, as the gas amplification changes, the amplitude of afterpulses becomes proportional to the square amplitude of the primary pulse, and that the coefficient of proportionality can serve as a criterion for comparing the emission properties of cathodes made of various materials. Such a comparison was performed for cathodes of stainless steel, copper, beryllium and aluminum alloys. It was found that phosphatizing of aluminum produces a coating, which essentially reduces the photoeffect on the cathode. Unlike anodic oxidation, a phosphate layer possesses sufficient conductivity that prevents spontaneous discharges in a counter caused by accumulation of electrical charges followed by an electrical breakdown of the coating layer.     

Development prospects for nondestructive testing of heterogeneous nonmetallic materials by the parameters of electrical response to a shock action

Theoretical and experimental research has been conducted into the mechanisms of generation of electric fields under elastic shock excitation of heterogeneous nonmetallic materials that contain two types of mechanoelectric transductions, viz., double electrical layers at interphase boundaries and piezoelectric inclusions. Using the example of electrical responses from samples of heavy- and light-weight concretes and based on numerical modeling results, prospects are shown for using this phenomenon in nondestructive testing of heterogeneous nonmetallic materials that do not contain piezoelectric inclusions, e.g., layered and reinforced ones.     

A differential double-coil inductive transducer for measuring electrical conductivity

A differential system of two double-coil inductive transducers for the contactless measurement of the electrical conductivity of conducting materials has been presented. The differential system can be employed in applications that require smaller measurement uncertainty than that provided by the single-transducer system. A mathematical model of the differential system is based on the model of a single double-coil inductive transducer; in this case, a so-called processing function is defined as a ratio of voltages at the measurement coil terminals with and without the test sample. The relative differential voltage of the differential system is derived as a difference of processing functions of two single transducers and depends on a relative difference between conductivities of the test and reference samples. The conductivity of the test sample is obtained either using precalculated graphs or by numerically processing the equation of the differential voltage. In order to verify the obtained theoretical results, experimental investigations have been carried out using a computer-controlled measurement system with the differential system of the transducers. The conductivity measurements have been carried out using samples made of aluminum rods. During the measurements, the temperature of the reference sample was equal to room temperature (20 degrees C), whereas the temperature of the test sample was changed in the range of 0-20 degrees C to obtain the conductivity variation. The obtained experimental results confirmed the accuracy of the theoretical model of the differential transducer.     

Use of Artificial Neural Networks in Identification of Modulated Pulses Due to Flaws

The analysis of a number of publications proved that artificial neural networks show much promise in identification of signals and images in nondestructive testing. A three-layered neural network with backward propagation has been used in separating noisy signals due to flaws from spurious signals (due to a slant or separation of an eddy-current transducer) in the process of eddy-current testing. Network characteristics at different numbers of neurons in its layers have been investigated. Probabilities of signal identification at different rms noise intensities have been determined.     

Thermal response simulation for tuning PID controllers in a 1016 mm guarded hot plate apparatus

A mathematical model has been developed and used to simulate the controlled thermal performance of a large guarded hot-plate apparatus. This highly specialized apparatus comprises three interdependent components whose temperatures are closely controlled in order to measure the thermal conductivity of insulation materials. The simulation model was used to investigate control strategies and derive controller gain parameters that are directly transferable to the actual instrument. The simulations take orders-of-magnitude less time to carry out when compared to traditional tuning methods based on operating the actual apparatus.The control system consists primarily of a PC-based PID control algorithm that regulates the output voltage of programmable power amplifiers. Feedback parameters in the form of controller gains are required for the three heating circuits. An objective is to determine an improved set of gains that meet temperature control criteria for testing insulation materials of interest.The analytical model is based on aggregated thermal capacity representations of the primary components and includes the same control algorithm as used in the actual hot-plate apparatus. The model, accounting for both thermal characteristics and temperature control, was validated by comparisons with test data.The tuning methodology used with the simulation model is described and results are presented. The resulting control algorithm and gain parameters have been used in the actual apparatus without modification during several years of testing materials over wide ranges of thermal conductivity, thickness, and insulation resistance values.     

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.     

Improving the Reliability of Eddy-Current Quality Control of Soldering in Current-Carrying Copper Joints and Expanding the Nomenclature of Inspected Joints in Energy Equipment

The possibilities of increasing the reliability of eddy-current quality control of soldering in current-carrying copper joints of the stator windings of electrical machines and expanding the nomenclature of inspected joints by using an improved eddy current transducer with a U-shaped core are investigated. To achieve this goal, rectangular cutouts were made in the poles of the U-shaped core, made of transformer steel plates, to allow the transducer to be mounted on a tested solder joint in two mutually perpendicular directions. Using such a transducer for testing allows one to induce closedloop eddy currents in the solder joint along these two directions, thus significantly improving the reliability of testing by virtue of all soldered surfaces in the joint contributing to the eddy-current transducer signal. The use of such a transducer also significantly expands the range of tested joints due to the possibility of exciting closed-loop eddy currents perpendicular to the direction of such joints (testing the side walls of the joints). It is shown that despite local changes in the distribution of electromagnetic field in the interpole space as compared to the case of no cuts, the presence of rectangular cuts in the poles of the U-shaped core of the eddy current transducer practically does not affect the accuracy of determining the degree of soldering of tested joints along and perpendicular to their direction.

     

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。