超导量子干涉器无损检测的应用与研究进展

超导量子干涉器（SQUID）由于其高磁场灵敏度、带宽宽、高空间分辨力在无损检测（NDE）领域有着重要的应用前景。近年来,针对SQUID NDE的研究取得了较快的进展,这为其用于实际工程奠定了良好的基础。综述了SQUID NDE的研究成果,包括应用领域、空间分辨力、噪声处理以及检测系统等。指出该技术的特点、存在的问题和发展方向。     

Stray flux effects on the magnetic hysteresis parameters in NDE of low carbon steel

The magnetic minor hysteresis loops and parameters of low carbon steel plate samples annealed at different temperatures have been measured and compared with the results of ring samples. The influences of stray flux in the fringe areas of the plate on the magnetic properties were discussed with the help of a finite element approach. It is found that the coercivity H_C and the hysteresis loss W_H of all of the plate samples sharply deviate from the values of the corresponding ring samples with the same applied field amplitude H_a larger than 3000 A/m. It is proposed that the fringe areas of the plate sample are magnetized by the stray flux to an irreversible state at large Ha, and the remanent fields act against the applied field in the inverse direction, resulting in the extreme increase of H_C and W_H. Although these parameters measured at high-applied field can reflect the microstructure changes, low field results are preferable for the practical use.     

直流超导量子干涉器无损检测的原理与应用

直流超导量子干涉器在弱磁测量领域有着广泛的应用，其中无损检测是它的重要应用之一，相对传统的电磁检测，该检测方法具有高灵敏度、高带宽和高空间分辨率的特点。介绍了该方法的检测原理和应用。     

Feasibility of magneto-optic flaw visualization using thin garnet films

We investigate the feasibility of using rare-earth iron garnet films grown on (111)-oriented substrates as magneto-optic indicator films for the visualization of magnetic leakage fields in non-destructive evaluation. In most cases the leakage field of the defect has a strong component in the film plane. The influence of this in-plane dc magnetic field on the image formation is investigated. It is shown that the presence of a strong in-plane magnetic field allows one to extend the dynamic range of the out-of-plane field imposed by the uniaxial anisotropy field H_A. On the other hand, an in-plane field reduces the sensitivity. The guidelines for selecting parameters of magneto-optic indicator films are given.     

Evaluation of eddy current probes based on local field excitation

The paper deals with the eddy current testing by means of a technique based on local field excitation, with the objective to enhance sensitivity and spatial resolution of flaw detection. Two modifications of innovative eddy current probes are presented. Results of the application of the probes for an examination of thin Inconel plate specimens with small artificial defects on the opposite surface are compared. The criteria for comparison are signal-to-noise ratios and spatial resolution of the responses obtained. Performance of the probes is analyzed on the basis of the study of the distribution of their excitation fields with application of magneto-optic sensors and finite element modeling. The decrease of the local extent of the excitation field has been found to be the main cause of sensitivity decrease of the probes to detect opposite-surface defects.     

直流超导量子干涉器的无损检测研究

利用高温直流超导量子干涉器（DC SQUID）建立一套无损检测装置，对无磁不锈钢材料受到外力冲击后产生的剩余磁场进行了探测，利用电磁激励的方法，对有内部缺陷的铝板进行了试验研究，并对激励频率的选择进行了初步的讨论。     

On the role of material property gradients in noncontacting thermoelectric NDE

Inclusions and other types of imperfections in nonmagnetic metals can be nondestructively detected by noncontacting magnetic measurements that sense the thermoelectric currents produced by directional heating and cooling of the specimen. The detectability of small and/or weak imperfections is ultimately limited by the intrinsic anisotropy and inhomogeneity of the material to be inspected. This paper investigates the spurious magnetic signature produced by the simplest type of macroscopic inhomogeneity when the material properties exhibit a linear spatial variation in the cross section of a slender bar. An analytical method has been developed for calculating the normal and tangential magnetic fields produced by the resulting thermoelectric currents. Experimental results from a highly inhomogeneous artificial copper/brass sintered specimen were found to be in very good quantitative agreement with our theoretical predictions and fully verified our analytical model. Similar measurements on a weakly inhomogeneous Ti–6Al–4V titanium-alloy bar were also shown to be in very good qualitative agreement with the predictions of the analytical model although the unexpectedly high magnitude of the observed signatures could not be verified by conventional contact measurements, therefore further efforts are needed to better understand the underlying physical phenomenon and clarifying the relationship between the strength of the signature and the very complex microstructural features of this popular high-strength alloy.     

Analytical solution for interaction of an arbitrary frequency curved rectangular inducer with a transverse ring shaped groove surrounding a long conductive cylinder

Field distributions around a transverse flaw surrounding a conductive cylinder which is excited by a three-dimensional inducer at arbitrary frequency are presented analytically. The solution is obtained by developing a two-dimensional Fourier series model and using Bessel functions in the third dimension. The metal is assumed as a lossy material and all possible field components in the conductor are expanded. After applying the mode-matching technique, a linear system of AX=B is solved to obtain the unknown coefficients. The accuracy of the proposed modeling technique is confirmed by comparing our results with those obtained by CST finite integration code.     

基于瞬态A_r方程的非线性涡流无损评价数值模拟

就一简化的三维磁性材料数值计算模型,对其非线性涡流信号进行了数值模拟试验。基于变形磁矢量位(Ar)低频涡流场的控制方程改良并开发了用于计算非线性涡流检测信号的数值模拟程序,得出非线性涡流检测信号与磁性材料因塑性变形而产生的磁导率变化之间的相关性,开发了非线性涡流信号数值模拟程序,利用开发的数值模拟程序计算非线性涡流检测信号,采用不同初始磁导率等效模拟试件不同塑性变形程度,得出了模拟信号的谐波幅值与塑性变形的关联性。对比非线性涡流数值模拟结果和试验检测结果,证明了塑性变形导致的磁导率变化是非线性涡流检测信号变化的直接诱因。     

Experiment and simulation study of 3D magnetic field sensing for magnetic flux leakage defect characterisation

Magnetic flux leakage (MFL) testing is widely used to detect and characterise defects in pipelines, rail tracks and other structures. The measurement of the two field components perpendicular to the test surface and parallel to the applied field in MFL systems is well established. However, it is rarely effective when the shapes of the specimens and defects with respect to the applied field are arbitrary. In order to overcome the pitfalls of traditional MFL measurement, measurement of the three-dimensional (3D) magnetic field is proposed. The study is undertaken using extensive finite element analysis (FEA) focussing on the 3D distribution of magnetic fields for defect characterisation and employing a high sensitivity 3-axis magnetic field sensor in experimental study. Several MFL tests were undertaken on steel samples, including a section of rail track. The experimental and FEA test results show that data from not only the x- and z-axes but also y-axis can give comprehensive positional information about defects in terms of shape and orientation, being especially advantageous where the defect is aligned close to parallel to the applied field. The work concludes that 3D magnetic field sensing could be used to improve the defect characterisation capabilities of existing MFL systems, especially where defects have irregular geometries.     

Mechanical damage detection using magnetic flux leakage tools: modeling the effect of dent geometry and stresses

We have used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses. Strain distribution information around the dent was obtained from an earlier work using finite element structural modeling. In the magnetic FEA dent model, the localized residual stresses were simulated by assigning appropriate values of magnetic anisotropy to the relevant magnetic regions. The simulated flux leakage patterns were found to be in good agreement with the experimentally observed MFL patterns associated with dent shape as well as with the stress effects from the dent.     

Nondestructive evaluation of multilayered paint films in ambient atmosphere using terahertz reflection spectroscopy

The reliability of material characterization with terahertz (THz) waves is typically compromised by irrelevant signals present in the THz measurements. These are well observed in the investigation of layered materials in humid environments, causing difficulty in accurate analyses. In this article, we suggest a realistically employable method of analyzing angled THz reflection measurements in ambient atmosphere for qualitative monitoring and evaluation of multilayered paint films. In particular, we present successive decomposition of THz sample signals for individual identification of each constituent layer in the samples. It is shown that the extracted spectrum of each paint layer presents sufficient information for effective monitoring of the multilayered structures. In this process, THz spectra of the marine paints EH2350, Interthane 989, BEA777, and ENA300 are reported for the first time. Our experimental findings show promise in highly effective nondestructive inspection of layered structures for real-world evaluation applications.     

Magnetic NDT Technology for characterization of decarburizing depth

From practical point of view, determining the decarburizing depth is important in quality control of steel parts as it has undesirable effects on the mechanical properties such as hardness, wear and fatigue resistance. Traditional destructive methods of determining the depth of decarburized layer include metallographic and hardness test which are time-consuming and costly. Since response to eddy current is sensitive to chemical composition as well as microstructure of the material under consideration, the non-destructive method can be used in determining the depth of the decarburized layer in steel parts. It is mainly due to the difference in the microstructures, and as a result, in the magnetic properties of the decarburized layer with other parts of the specimen. In the present study at the first step, the magnetic properties of decarburized carbon steel bars (0.45 wt.% C) were evaluated using an electromagnetic sensor and correlated with the microstructure changes from surface to the core of the sample. At the second step the steel bars were held in 900 °C for different period of times and the depth of decarburizing layers were measured using hardness testing. Finally, the non-destructive eddy current technique was used and the response of test samples to the induction current including primary and secondary voltages, normalized impedance, phase angle and harmonic analysis parameters were investigated. Results show an acceptable accuracy in comparison to the destructive method.     

压应力对Sm-Fe-B薄膜磁致伸缩性能的影响

压应力对Sm-Fe-B磁致伸缩性能的改善有重要影响,但是其大小对磁致伸缩特性变化趋势的研究很少,而且还未见到压应力对磁各向异性影响的报道。本文利用特制夹具,使玻璃衬底在镀膜过程中受到不同应力作用,镀膜结束后,当玻璃衬底从夹具取下后,利用其恢复到原来状态,可以对稀土Sm-Fe-B薄膜产生压应力作用。通过调整夹具使衬底具有不同的预应力,可得到受到玻璃衬底不同压应力大小作用的薄膜样品。利用LK-G150激光微位移传感器与交变梯度磁强计（AGM）分别测试薄膜悬臂梁自由端偏转量与磁滞回线,以研究具有不同压应力对薄膜的磁致伸缩性能的影响,并且利用磁力显微镜（MFM）测试了薄膜样品垂直表面的磁畴分布情况。实验结果表明：受到压应力作用的薄膜易磁化轴都位于膜面内,以面内各向异性为主,磁畴结构基本分布在面内。随着压应力的增加,易磁化轴由膜面内的短轴转向膜面内的长轴,这一转变有利于器件的设计,但是磁畴在垂直膜面方向略有提高,薄膜的低场磁致伸缩性能也随着压应力的增大而有显著提高。     

35号冷轧钢在不同阶段应力作用下的磁效应特征

在反复加载-卸载条件下,测量了35号冷轧钢试件在不同的最大拉应力作用下,试件表面某确定点漏磁场随拉应力的对应关系。试验结果表明,当最大拉应力σmax为255～496MPa时,磁感应强度-应力(B-σ)近似呈线性关系变化;当σmax为535～611MPa时,B-σ关系由直线变为折线,并且折线极值点的位置处于100～200MPa之间;当σmax为637～662MPa时,B-σ曲线极值点的位置处于382MPa处,磁感应强度的变化量迅速增大;当σmax为687MPa时,B-σ关系曲线的极值点移到458MPa处,磁感应强度的变化量进一步增大。试验得到了试件在拉应力作用下的磁化关系,证实了可以通过磁信号的大小对试件的安全性作出评估。     

NDE ultrasonic methods to characterise the porosity of mortar

Premature damage of mortar and concrete structures, due to environmental action, demands procedures to estimate durability of this type of components. Mortar or concrete composition (e.g. grain size, type and percentage of sand) may have some influence in the durability, but it is mainly related to porosity, which determines the interaction between aggressive agents and material. In this work, several IDE ultrasonic methods to estimate porosity of mortar are presented and evaluated. In these methods, porosity is related to (1) the material structural noise, (2) sound velocity and (3) ultrasonic attenuation. In all these methods, mortar is consider to be formed by only two phases: solid and pores.     

用相机测量金刚石膜透光性的研究

为了方便测量、记录和交流金刚石膜的透光性,对用相机测定金刚石膜透光性的技术问题进行了研究。其原理是由相机的感光度、光圈、快门速度先得到一张级差为20%的25级金刚石膜透光性的速查表。测量中,得知膜的快门速度后查表,即可知膜的透光性级数和透光率。该法表征金刚石膜透光性的方式,可适用于多散点单参数膜25级平面坐标图示法和单散点多参数膜相关信息元素的多项式法。该方法快速方便、简单可靠,无需大型设备,保证了金刚石膜的完整性,觧决了整片金刚石膜透光性的测量、表征和分级的问题。     

Automatic flaw detection in NDE signals using a panel of neural networks

The magnetic flux leakage (MFL) method is widely used for the assessment of the condition of off-shore cables, gas pipes and aerial tramway cables. At Empa, a measuring device was developed to use the physical effect of MFL for large diameter steel cables as used in civil engineering structures.It is considered that the automatization of the flaw detection task would offer great advantages, both from an economic point of view as well as in terms of reliability. In this work the application of a feature extraction model based on an analytical approximation of the MFL intensity is presented. Parameters that are closely related to the size and position of a defect are used as fitting variables in the solution of the inverse problem that links the recorded MFL intensity to the flaw that generates it.Using these significant parameters a committee of neural networks is trained in order to obtain a robust flaw detection algorithm.     

Preventing or accelerating galvanic corrosion through the application of a proper external magnetic field

The effect of an external magnetic field on the corrosion behaviour of a galvanic couple, zinc (Zn)–stainless steel (SS 316L), has been investigated in a 0·055 mol L^?1 potassium chloride (KCl) solution. The impact of the orientation as well as the magnetic flux density B (Wb m^?2) on the corrosion progression of the galvanic couple, is evaluated heuristically by monitoring the corrosion potential E_corr (mV) and the current density I_corr (μA cm^?2) of the system. A strong influence of the magnitude and orientation of the magnetic field on the Zn–SS316L galvanic couple corrosion was observed, whereas the field was proven to act either protective or accelerating in terms of corrosion.