脉冲涡流圆柱型探头参数的优化设计

介绍了脉冲涡流检测的工作原理。通过有限元对圆柱型探头不同参数的线圈周围磁场和被检试件中感生涡流的分布进行了仿真,得出了扁平型的激励线圈产生的磁通量能够有效地渗透到被检试件的内部,有利于系统检测灵敏度的提高。通过不同激励频率在试件中的涡流密度、渗透深度的分析,能够根据脉冲涡流检测对象,得到探头中所用的最佳工作频率,为脉冲涡流探头的实际检测奠定基础。     

脉冲涡流矩形传感器参数仿真优化设计

脉冲涡流矩形传感器是近年来涡流无损检测的研究热点。采用COMSOL有限元仿真软件建立了矩形探头有限元仿真模型,以电导率变化为变化因子,使用单因素轮换法对矩形探头的尺寸比例进行了优化设计。通过仿真实验和数据分析,得出矩形探头长宽高比例为2∶1∶1.5时,探头的灵敏度、线性度最佳。本仿真优化结论可为使用脉冲涡流进行矩形探头缺陷或应力检测提供参考。     

脉冲激励远场涡流管道检测技术的有限元仿真

研究了脉冲激励下的远场涡流管道检测技术,采用有限元仿真的方法对检测系统参数对检测结果的影响做了详细的分析。表明该技术将远场涡流和脉冲激励的优势有效结合,能提取较多检测信息,可同时测量管道内径和内、外壁缺陷信息,且具有信号幅值高,功耗低的优点。     

激励参数对脉冲涡流缺陷检测的仿真分析

脉冲涡流检测技术是一种新兴的电磁无损检测技术,激励参数与脉冲涡流检测灵敏度、涡流渗透深度密切相关,选择合适的激励参数十分必要。采用COMSOL有限元仿真软件建立了脉冲涡流圆柱型探头的有限元模型,分析了不同幅值、不同占空比以及幅值与时间的乘积相同的情况下,对金属部件表面下缺陷检测的影响。通过有限元仿真分析,提出增大激励幅值可以提高检测的灵敏度,增大占空比可以提高涡流的渗透深度的结论。该结论为工程实践金属内部缺陷检测提供了一定的参考价值。     

敫励参数和试件电磁参数对脉冲涡流检测影响的仿真分析

脉冲涡流检测技术已成功应用于带包覆层容器和管道壁厚检测。然而,由于铁磁性材料脉冲涡流检测机理的复杂性,目前缺乏对检测信号影响因素的有效分析方法。首先利用有限元仿真方法建立了脉冲涡流检测模型,并用试验验证了模型的正确性;然后研究了重复频率、占空比及边沿斜率等激励参数对检测信号的影响,为脉冲涡流检测激励模式的选择提供参考;最后分析了试件电磁参数对检测信号的影响,为脉冲涡流检测结果的解释提供依据。     

接收线圈位置对脉冲涡流检测灵敏度的影响

研究了对带包覆层管道的内部腐蚀进行脉冲涡流检测时,接收线圈的位置变化对检测灵敏度的影响,进行了探头置于激励线圈下不同位置的有限元仿真和试验研究。有限元仿真结果表明:在轴向和周向2个方向都是当检测线圈位于激励线圈边缘正下方时检测效果最好,其灵敏度分别为0.61、0.60。验证试验表明:在轴向和周向2个方向上,最佳检测位置都是位于激励线圈边缘正下方,其灵敏度分别为0.26、0.27。试验结果与仿真结果基本一致,表明接收线圈在激励线圈外边缘正下方附近时,检测灵敏度达到最大。研究结果有助于带包覆层管道腐蚀的脉冲涡流检测的传感器设计。     

带保温层管道腐蚀缺陷的脉冲涡流检测技术仿真

脉冲涡流检测技术是近几年发展起来的一种新型无损检测技术,可以应用于金属管道和金属板的内腐蚀检测。以低碳无缝钢管的内壁腐蚀作为检测对象,建立了针对脉冲涡流检测的ANSYS有限元仿真模型,分析了磁场仿真的理论基础,列出了仿真分析的具体步骤。为ANSYS有限元仿真软件在脉冲涡流检测中的应用提供了参考,为脉冲涡流检测设备的研制提供了依据。     

基于刀片式激励线圈旋转的脉冲涡流探头

脉冲涡流检测裂纹时,微裂纹在感应涡流中产生的扰动微弱,检测信号的信噪比低;另一方面,单向扫查下的常规脉冲涡流探头难以获得多向裂纹检测的最大灵敏度和判断裂纹方向。提出一种采用机电旋转脉冲涡流激励线圈的检测方法,实现了多方向微裂纹的高灵敏度检测。刀片式激励线圈具有明显的聚磁性与方向性,机电旋转激励线圈后可以获得不同转角下的接收信号,将该接收信号与基准信号进行差分,提取出微小的峰值变化量,得到角度与峰值变化量之间的图谱。试验验证与测试结果表明：基于刀片式激励线圈在空心接收线圈内旋转的脉冲涡流探头不仅具有亚毫米级裂纹深度区分的检测能力,且能有效分辨裂纹方向,误差为±5°。     

脉冲漏磁检测中的涡流效应

为了解脉冲漏磁检测中涡流效应的特点,奠定进一步分析脉冲漏磁检测信号的基础,建立了脉冲漏磁检测的有限元仿真模型,观察了检测中瞬态磁场和感生涡流的分布,分析了感生涡流特征量的特点及影响因素。结果表明,脉冲漏磁检测中,瞬态磁场和感生涡流总体上符合集肤效应并相互影响,其中感生涡流具有渗透深度浅、感应强度大的特点,涡流密度峰值时间在深度方向上有较强的分辨率。电导率和磁导率影响感生涡流的渗透深度和密度峰值时间在深度方向上的分辨率;脉冲激励上升时间常数只影响感生涡流的渗透深度,而和密度峰值时间在深度方向上的分辨率无关。     

飞机多层结构铆钉周围裂纹脉冲涡流检测传感器参数优化

飞机多层结构铆钉周围埋藏裂纹检测是无损检测领域的一个难点和热点,脉冲涡流能够对这种裂纹进行有效的检测.针对这种缺陷检测,本研究采用了一种双激励线圈且用隧道磁电阻(TMR)为接收的新型探头.双激励源反向联接,激励电流不至于过大,但磁场却能达到局部聚焦的作用.通过大量试验对该传感器参数进行优化选择,以提高传感器的检测灵敏度.试验结果表明:当激励线圈绕制180 匝、两激励线圈间距为20~30 mm、单个线圈水平夹角为60°~90°、且TMR位于裂纹正上方时探头的检测灵敏度最大.该研究结果可为飞机多层结构铆钉周围裂纹脉冲涡流检测探头设计提供参考.     

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。     

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.     

3-D movement simulation techniques using FE methods: Application to eddy current non-destructive testing

In this paper, sample calculations were performed with a three-dimensional (3-D) numerical method to describe the response of an eddy current (EC) probe to defects in a conducting plate. The governing field equations are given in terms of coupled magnetic vector and electrical scalar potentials and solved using a 3-D finite element method implemented in Matlab environment. The displacement of the sensor operating in absolute or differential mode is simulated using three methods: The first and second methods known, respectively, as the nodal interpolation technique (NIT) and the Lagrange multiplier technique (LMT) consist in ensuring the connection between fixed and moved 3-D independent meshes. The third method known as the properties assignment technique (PAT) is based on the geometrical band.In this work, these methods are used to compute the real and imaginary parts of the impedance correlation at every position of the coil(s). This allows the characterisation of the presence of a defect through the EC distribution.     

Impedance inversion in eddy current testing of layered planar structures via neural networks

The inversion of eddy current probe impedance measurements is widely recognized as a complex theoretical problem whose solution is likely to have a significant impact on the characterization of materials. In this paper the evaluation of the conductivity profile of a layered planar structure is performed after inverting the impedance of a circular air-cored probe coil, of rectangular cross-section, using multilayer perceptron neural networks, trained via the back propagation learning algorithm. The merits of the method are illustrated in the light of two engineering examples.     

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。     

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。     

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.     

Pulsed eddy current testing with variable duty cycle on rivet joints

In pulsed eddy current testing, repetitive excitation signals with different duty cycles have different spectral representations. This work studies the influence of duty cycle on the ability to detect holes and EDM notches beneath rivet heads in subsurface layers of stratified samples. Feature patterns for the integrity of rivet joints are proposed and verified. The proposed method has the added advantage in that no reference sample is needed while employing multiple pulse measurements, with different pulse widths. Experimental testing and modelling approaches are discussed in connection with defect depth quantification, which can be extended to the quantification of complex defects.     

Combined analytical-numerical approach to the voltage of a cylindrical coil with pulsed current

This paper presents a combined analytical-numerical approach to solving the pulsed eddy current problem accurately and quickly. Considering the displacement current, the analytical solution to the voltage of a cylindrical coil above a laminated conductor in the complex-frequency domain is deduced by Laplace transform. The time-domain induction voltage values of a cylindrical coil with a pulsed current are calculated by the fourth-order integro-differential FFT-based numerical inversion of Laplace transform. At the same time, the time-domain analytical solution to the induced voltage of a cylindrical coil with a pulsed current above a half-infinite non-ferromagnetic conductor is derived, and has been verified by comparison with Finite Element Method (FEM) simulation results. The calculation results prove that the adopted numerical inversion method of applying Laplace transforms to the pulsed eddy current problem has a high accuracy and fast convergence. The transient voltages produced by a square-wave current excitation when considering the displacement current in the vacuum area are higher than those when ignoring the displacement current, by as much as 27.7% at certain times. The higher the lift-off is, the smaller the voltage peak is and the faster the voltage drops. As the application of this method, the induced voltages are computed in the measurements of metal's thickness and metal coating thickness.