共查询到20条相似文献,搜索用时 31 毫秒
1.
In this paper a new differential eddy current testing sensor is proposed which is composed of two planar circumferential gradient winding spiral coils. The eddy current testing sensor can detect out the existence of crack in conductive material surface and furthermore the crack extension direction because of the circumferential gradient winding spiral structure of coil. We study the detection principle of crack extension direction and carry out experimental test. The test results show that the impedance of circumferential gradient winding coil mainly varies with crack extension direction and width. Based on impedance plane analysis we extract the features which can indicate the crack characteristics and study on the inverse quantitative evaluation of crack extension direction and crack width. 相似文献
2.
The results of a theoretical and experimental study of planar rectangular coils in eddy-current NDE are presented. Three fundamental cases are examined: a planar coil (i) in free space, (ii) above a defect-free conductive half-space and (iii) centered above a long, uniform crack. Closed-form expressions for the coil impedance are presented for these three cases and the theoretical predictions are validated against experiment using a series of coils with different aspect ratios and both non-magnetic and magnetic plates. While the change in normalized coil impedance due to the half-space depends only weakly on the coil aspect ratio, the change in normalized impedance due to the crack depends strongly on coil aspect ratio with the maximum normalized response observed for an aspect ratio of 1:1, i.e. for square coils. In contrast to planar circular coils, the response of planar rectangular coils depends on their orientation with respect to the crack. This orientation dependence is investigated in detail. 相似文献
3.
The surface magnetic field measurement (SMFM) technique has proved to be an accurate means for crack detection and sizing cracks in ferrous metals. The technique involves the use of two U-shaped current-carrying wires of sufficiently high frequency while measuring the discontinuity in the resultant magnetic field at the crack edge with an appropriate magnetic field sensor. In this work, we describe a mathematical algorithm to obtain the crack signal from the output of an induction coil used in a SMFM probe. We also discuss the measurement errors due to the coil size and shape. To reduce the measurement errors, we present an algorithm in which the crack signal is recovered by appropriate deconvolution of the coil output signal and its spatial transfer function. The algorithm is then used to recover crack signals for various coil shapes and sizes. The study of the results demonstrates the effectiveness of the algorithm in the case of large coils. 相似文献
4.
5.
The performance of circular and square coils in electromagnetic–thermal non-destructive inspection of conductive plates is investigated numerically for various configurations. A coil is most effective when placed at an optimum distance from the plate, equal to 1/4 of the diameter for a circular coil or 1/4 of the side for a square coil. At this distance, the coils considered are equally efficient in detection of cracks. Substantial differences exist only when the coils are placed very close to the plate but then become less effective. For that case, the planar coils give better results. A coil with a section comparable in area with the inspected surface cannot inspect the whole surface effectively in a single inspection. The support of a smaller section coil is necessary in order to clarify the shape of the cracks that are not clear. 相似文献
6.
Pingjie Huang Guangxin Zhang Zhaotong Wu Jinhui Cai Zekui Zhou 《NDT & E International》2006,39(7):578-584
The forward problem of eddy current detection of defects by scanning conductive multi-layered structures is investigated and the change of the probe coil impedance is modeled by using finite element analysis method. Based on the ANSYS software a fast simulating program is developed and then the coil impedance changes due to the existing of defects in different lengths, shapes and at different locations in conductive multi-layers are calculated. An experimental eddy current testing system combined with a scanner is established and scanning testing experiments are carried out. The simulation and experimental results are compared. The agreement of them shows that the technique studied is promising and can help us to understand the probe responses and can be applied to the inversion model to determine the defect parameters in many important fields ranging from aerospace to energy and transportation industries. 相似文献
7.
8.
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. 相似文献
9.
This paper addresses the problem of practical crack identification in electrically conducting specimens using only boundary measurements. The method is commonly referred to in the literature as Electrical Impedance Tomography (EIT).Crack identification is determined from the electrical impedance distribution, which amounts to solving an inverse problem, starting from boundary measurements. Whereas this kind of inverse problem has been extensively addressed in its theoretical and numerical aspects, there is a scarcity of experimental results aimed at examining the applicability of the method for real conditions.We present new experimental results, based on a simple identification methodology. The efficiency and limitations of this method are assessed through a series of numerical simulations and laboratory experiments on two-dimensional geometries. Following a preliminary numerical validation stage, actual crack detection is carried out on a discrete network of resistors, as an approximation to Laplace's equation. Next, experiments are carried out on a continuous conductive medium, containing one and two flaws. Our results show that EIT is a promising candidate for crack identification in real life conditions with a potential for multiple crack detection. 相似文献
10.
11.
为了有效利用脉冲涡流信号的低频成分检测钢板内部裂纹缺陷,提出了脉冲涡流同步采样方法。介绍了该方法的工作原理;采用在钢板上加工不同规格矩形槽的方法模拟钢板的裂纹缺陷;设计了由激励线圈和检测线圈构成的传感器,实现脉冲涡流信号的提取;采用数据采集卡采集信号,以Labview为平台,实现同步采样方法的软件设计。对钢板缺陷的检测和试验数据的分析,证明了脉冲涡流同步采样方法在钢板内部裂纹缺陷检测中具有较高的灵敏度,可以有效识别钢板内部裂纹缺陷。 相似文献
12.
对管线钢L245热轧卷边部裂纹缺陷产生原因进行了分析,并研究了此钢种高温热塑性行为,认为钢种特性是导致热轧卷边部裂纹缺陷产生的根本原因,但通过合适的工艺制度可以减少该缺陷的产生。 相似文献
13.
The performance of electromagnetic-thermal non-destructive inspection is investigated experimentally by eddy current thermography. The experiments concerned the detection of the crack in ten square aluminum plates at various positions and orientations. For the excitation are employed two circular coils with an outer diameter either smaller or comparable to the plate side. Crack detection is based not only on the thermograms, but on data processing techniques as well. Despite the fact that the performance of the infrared camera used is relatively low and the exciting frequency was only 50 Hz, the coil with small section detected effectively the nine cracks out of the ten while the coil with large section detected effectively seven out of ten. 相似文献
14.
建立带有单边裂纹的无限大金属薄板模型,给出脉冲放电瞬间的温度场,应用一维条件下的热弹塑性理论,导出了单边裂纹金属构件电磁热止裂后的一维残余应力解;对带有单边裂纹的导电薄板脉冲放电后裂纹尖端产生的残余应力进行数值分析,理论与数值分析结果基本吻合;对40CrNiMo试件的残余应力超声波无损检测发现,止裂后残余应力变大。研究表明,在对带有单边裂纹的导电薄板进行电磁热止裂时,裂纹尖端周围温度急剧升高,使得裂纹尖端受热膨胀,由于裂尖受到周围材料的刚性约束,在受热和冷却过程中会残留一个压缩塑性应变,其产生的残余应力可有效的抑制裂纹扩展。 相似文献
15.
为了解决09CrCuSb耐酸钢热轧卷分条切边过程中的边部分层问题,采用金相显微镜与SEM-EDS分析仪研究了3种09CrCuSb热轧卷边部缺陷,即边部分层、边部的端面凸起和平行于轧制方向的端面纵裂纹。结果表明,本边部分层缺陷实际上是由热轧侧导挤压所致,校正侧导位置后未再发生,判定边部分层缺陷产生原因的关键在于分层缺陷的内表面状态。端面凸起是因为连铸机精度偏差使铸坯发生边角裂,控制连铸机对弧与辊缝偏差在0.5 mm以内,缺陷发生率从5.4%降低到0.2%以下,端面凸起缺陷实际上是热轧卷烂边的初始形态。端面纵裂纹缺陷是因为连铸坯窄边存在群簇状气泡及钢种本身裂纹敏感性较强,通过降低连铸塞棒和水口氩气到4~6 L/min,按标准下限控制裂纹敏感性元素,缺陷发生率从8.7%降低到了0.45%。为控制09CrCuSb热轧卷边部缺陷提供参考。 相似文献
16.
A novel method for FDTD numerical GPR imaging of arbitrary shapes based on Fourier transform 总被引:2,自引:0,他引:2
Ground penetrating radar (GPR) systems are very powerful tools with a wide range of advantages in non-destructive testing. Target detection is one of the serious results of GPR application. The landmine detection in the soil and reinforcement bars and holes in the concrete is some of the GPR object detection examples. In this research, the targets are modeled in different cases, an air hole or a conductive material. A cracked surface is also modeled for both conductive and dielectric media. For modeling, the three-dimensional (3D) finite difference time-domain (FDTD) method is applied. Perfectly matched layer (PML) absorbing boundary condition is used for simulating the physical absorbers and free space. The results were shown in time domain. The difference between results helps to distinguish the target depth and electrical properties. For better specification of the target shape, a transform in frequency domain is used. This transform contains a Fourier transform in a selected frequency. The results show a sudden change in the frequency response over the hole or target scanning. By this idea, the shape of any arbitrary hole or crack can be extracted. 相似文献
17.
Expansion of a low conductive metal tube by an electromagnetic forming process: Finite element modeling 总被引:2,自引:0,他引:2
Chansun Shin Hyung Ha Jin Jung Gu Lee Dong-Jin Lee Chang-Kyu Rhee Jun-Hwa Hong 《Metals and Materials International》2008,14(1):91-97
The expansion of a metal tube by means of an electromagnetic forming (EMF) process is attractive because EMF has a high forming
rate and can reduce residual stress. The forming forces in EMF are Lorentz forces. They are derived from a repulsive interaction
between a transient electric current induced in a coil with the aid of a capacitor bank and an eddy current induced in a metal
tube by means of a transient current. Highly conductive metals are suitable for EMF-based tube expansion but tubes of low
conductive metals are often used for industrial purposes. We studied various methods of using EMF to increase the formability
of low conductive metals. In particular, we used a finite element method to compute an electromagnetic field coupled with
temperature and deformation of a metal tube. Our results show that a highly conductive layer can increase the formability
of a low conductive metal. 相似文献
18.
19.
在分析铝合金铸轧卷产生工艺裂边原因的基础上,从减小铸轧区长度和改进耳子的开角进行试验,减少或避免了铝合金卷材的工艺裂边. 相似文献