基于数理统计的缺陷涡流检测定量方法

针对涡流阻抗平面显示检测仪器对缺陷大小不能准确定量检测的难题,采用正态分布及一元线性回归分析的数理统计方法,对涡流检测定量方法进行研究,得出了涡流阻抗幅值与缺陷大小的数学规律。经试验验证,定量检测结果良好。     

Analytical modeling of the transient response of a coil encircling a ferromagnetic conducting rod in pulsed eddy current testing

Analytical solutions are obtained in the time domain for the electromagnetic response to the leading edge of a square pulse excitation of a multiple turn current coil, encircling a long ferromagnetic rod, in the linear permeability regime. The resulting equations, obtained using a magnetic vector potential formalism, describe the time-dependent progression of flux into and along the rod. Results are in agreement with finite element solutions obtained for the same geometry. The work is motivated by the requirement for rapid analytical solutions and insight into pulsed eddy current response during inspection of multilayer aluminum aircraft structures in the vicinity of ferrous fasteners.     

Thickness measurement of metal pipe using swept-frequency eddy current testing

Swept-frequency eddy current measurement of pipe thickness is studied in this paper. First, suitable frequency range of swept-frequency eddy current testing is determined by comparing sensitivities of relative reactance change with respect to pipe thickness and other parameters at different frequencies. Based on analytical solutions to pipe eddy current field, Levenberg–Marquardt algorithm and variable transformation, a method for solving inverse eddy current problem is developed. Finally, several inversion calculations are carried out and the results are close to the truth values. The low errors reveal that the method presented in this paper is appropriate.     

Structural analysis of CFRP using eddy current methods

Nondestructive inspection of carbon fibre-reinforced plastics (CFRP) using eddy current methods is not only based on the conductivity of the fibres. High frequencies (up to 10 MHz) enable the exploitation of capacitive effects reflecting the properties of the matrix. The paper presents a method using rotating eddy current probes to measure the anisotropic electrical properties. Potential applications of the method are structural identification of laminates and estimation of their degradation. For example, the strength properties of constructions based on unidirectional CFRP are very sensitive to small differences in fibre direction angle. Best detection of these angles could be obtained above 7.5 MHz. In addition, a signal perpendicular to the fibre orientation was found and termed the plateau effect. It is a result of capacitive connections between the fibres and presents new opportunities for the characterization of matrix properties.     

一种基于摆动式涡流传感器的焊缝跟踪方法

采用非接触电涡流传感器应用于焊缝跟踪,利用指数运算电路补偿传感器的线性度,从而加大了传感器的量程,消除了传感器在焊缝跟踪过程中的失真情况.选用摆动式涡流传感器检测焊缝偏差信息,实现复杂形状焊缝的平板对接I形坡口的自动跟踪.应用区域积分差值加权比较法对焊缝的偏差信息进行分析,消除了因板厚不均匀以及错位的误判,在采样数据点不变的情况下,提高了焊缝跟踪精度.结果表明,摆动式涡流传感器用于焊缝自动跟踪可行,跟踪效果好,为目前对自动焊缝跟踪技术的研究提供了一种新的方法.     

涡流检测技术在宝钢热轧轧辊上的应用

介绍了轧辊涡流检测仪的工作要求、设备组成和使用方法,指出对轧辊进行涡流检测可防止爆辊,减少轧辊磨削量。     

A practical hole testing technique using a meter display eddy current instrument

A practical technique for the detection of cracks emanating from holes was investigated for non-ferrous materials using the eddy current method. This technique is suggested when more appropriate test equipment is not available. An unshielded absolute pencil probe and a meter display instrument were utilized in the study. It was determined that holes with a minimum diameter of 6.5 mm can be tested efficiently for the detection of cracks at least 0.15 mm deep. For the equipment used, the hole depth that can be tested is limited about 11 mm if access from the other side is not possible. The detection capability was confirmed by an impedance plane display instrument using rotary differential probes.     

主成分分析法在脉冲涡流缺陷识别中的应用

在钢结构脉冲涡流缺陷识别中,通常采用信号的峰值幅度、过零时间、主峰面积等特征参数对缺陷进行表征。但上述参数相互关联,存在一定的信息冗余,增加了数据分析量及信息筛选难度,进而影响了缺陷识别的效率。针对上述问题,采用主成分分析法对脉冲涡流信号的6个特征参数进行降维处理,构造了一个主成分特征,减少了信息冗余;将上述主成分特征输入Logistic分类器,实现了对钢结构减薄缺陷的准确识别。结果表明:主成分分析法可以在确保缺陷识别准确率的情况下,有效减少分类器处理的数据量,提高缺陷识别效率。     

基于多频涡流信号处理的结构识别方法

提出了一种基于多频涡流信号处理的结构识别方法,该方法首先采用多频涡流仪获得低频绝对通道信号,通过旋转变换得到多组信号对,确定振幅最小的那一对,接着运用中值滤波技术获得整体信号幅度摆动趋势线,从而消除信号摆动影响,凸显结构信号;然后,根据结构幅度阈值和最小间距确定结构中心位置及其数量;最后,根据弯管和支撑信号特征,识别并显示这些结构。运用多组来自不同核电站的实测数据进行识别,结果显示了该方法的有效性。     

The application of uniform field theory to horizontal axis eddy current coils

This paper considers the application of the uniform field theory to the study of horizontal axis coils for eddy current testing. Both the 2D and 3D theories have been investigated, the theoretical results in both cases comparing quite well with the experimental results obtained. The reasons for the discrepancies between theory and experiment are discussed, but the overall conclusion is that the uniform field theory can be applied with a certain degree of success to the study of horizontal axis coils.     

Reduction of lift-off effects for pulsed eddy current NDT

The lift-off effect is commonly known to be one of the main obstacles for effective eddy current NDT testing as it can easily mask defect signals. Pulsed eddy current techniques, which are believed to be potentially rich of information, are also sensitive to the effect. An approach using normalisation and two reference signals to reduce the lift-off problem with pulsed eddy current techniques is proposed. Experimental testing on the proposed technique and results are presented in this report. Results show that significant reduction in the effect has been achieved mainly in metal loss and sub-surface slot inspection. The technique can also be applied for measurement of metal thickness beneath non-conductive coatings, microstructure, strain/stress measurement, where the output is sensitive to the lift-off effect.     

Transient response of a driver coil in transient eddy current testing

A solution is presented for the case of a driver coil encircling a ferromagnetic conducting rod. The differential circuit equation is formulated in terms of the rod׳s impulse response using convolution theory, and solved by Fourier transform. The final solution accounts for feedback between the ferromagnetic rod and the driver coil, providing correct voltage response of the coil. Also arising from the solution is an analytical expression for the complex inductance in the circuit, which accounts for real (inductive) and imaginary (loss) elements associated with the rod. Experimental results, obtained for the case of square wave excitation, show excellent agreement.     

焊接逆变电源与涡流检测融合设计及可行性分析

根据逆变焊接电源和涡流检测的原理,将涡流检测模块添加到逆变焊接电源中,实现了焊接加工和质量检测的成功融合。通过融合系统的焊接与检测实验,证明了系统不仅可以正常焊接加工,还能准确检测试样缺陷,实现了焊接与检测分时工作且互不干扰,大大提高了数字处理的利用率。     

Electrical conductivity measurement of ferromagnetic metallic materials using pulsed eddy current method

Pulsed eddy current testing (PECT) method for electrical conductivity measurement of ferromagnetic metallic materials is proposed. Based on time-domain analytical solutions to the PECT model of ferromagnetic plates, the conductivity and permeability are determined via an inverse problem established with the calculated and measured values of induced voltage. PECT method for conductivity measurement is verified by the four-point probe method on three carbon steel plates. In addition, the effects of the amplitude of pulsed excitation current and the lift-off of probe coils on measurement results are studied. PECT is an innovative, non-contacting method with good repeatability for electrical conductivity measurement.     

Remote field eddy current technique applied to non-magnetic steam generator tubes

Unlike the impedance plane analysis form of common eddy current testing (ECT), the remote field eddy current (RFEC) technique is a through-transmission effect that reduces problems such as lift-off normally associated with ECT. In the inspection of steam generator (SG) tubes, the real issue is to detect the minute cracks growing up from the outside. However, using ECT, it is considered infeasible to accurately find them from the inside because of the limitations of penetration of eddy currents. This paper describes a finite-element approach to the solution of time-harmonic electromagnetic fields for the RFEC technique based on a magnetic vector potential and an electric scalar potential. A comparison is made of experimental and finite-element predictions of electromagnetic phenomena under the inspection of non-magnetic tubes. For the cracks outside demanding high sensitive and precise measurements in the SG tube inspection, numerical results are given for parameters to design a RFEC probe.     

Bonded Terfenol-D composites with low eddy current loss and high magnetostriction

Bonded Terfenol-D composites,with high electrical resistivity and low eddy current loss,can be used in an alternating magnetic field with high frequency.However,the nonmagnetic binder impairs the magnetostriction of the composites.To achieve high magnetostriction and low eddy current loss,the mixture of the alloy powder and binder was compressed at low pressure in an oriented magnetic field.After this,the aligned samples were recompressed by cold isostatic pressing(CIP).Besides,the effect of particle size on the magnetostriction of the bonded Terfenol-D composites was also studied.The results showed that the bonded Terfenol-D composites had excellent magnetostriction when the particle size was 50-80 μm.The oriented magnetic field and CIP could improve the magnetostriction of the bonded composites,which reaches 1020×10-6.The bonded Terfenol-D composites had good compact structure and high density(7.24 g/cm3).The magnetic loss of the bonded Terfenol-D composites was 192 mW/cm3 at a frequency of 100 kHz in a magnetic field of 960 A/m,which was about one third of that of casting Terfenol-D alloys.     

焊接逆变电源与涡流检测融合设计分析

根据焊接逆变电源与涡流检测的工作原理,在焊接逆变电源中加入涡流检测激励与接收部分的模拟信号处理电路,而涡流检测的数字信号处理部分则与焊接逆变电源共用,实现焊接逆变电源与涡流检测的融合设计.焊接逆变电源主变压器输出的交流方波经过滤波后,以滤波器输出的正弦波作为涡流检测的激励信号,驱动涡流检测探头,涡流检测探头接收的信号经过放大、比较、检波及后续的数字信号处理进行缺陷判断,实现涡流检测.结果表明,该融合系统能够在不影响焊接的条件下为逆变电源增加涡流检测功能.     

国产涡流检测设备在轧辊磨削及检查中的应用

简述为提高轧辊使用寿命 ,降低生产成本 ,对在役轧辊实施自动检测的重要意义。介绍了上海宝钢益昌薄板有限公司采用的国产涡流自动检测设备的组成和功能。该厂采用该技术后 ,减少了轧辊磨削量 ,避免了爆辊事故 ,取得了较好效果。