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提出一种适合于金属亚表面缺陷的可视化无损检测方法——磁光/脉冲涡流成像方法。该方法以脉冲信号激励产生涡流,以激光对被检测物体的照射取代传统涡流检测的线圈探头,通过磁光传感元件将缺陷引起的磁场变化转换成相应的光强度的变化,由传统的显微镜、照明系统、偏振器和CCD图像传感器组成的光学系统将光强变化转换为“明”或“暗”图像,实现了对缺陷的实时成像检测。本文论述了磁光/脉冲涡流实时成像检测机理,给出了一种实验装置。通过对金属表面/亚表面缺陷实验,表明该检测方法快速、准确,可实现微/纳米级缺陷的成像检测。 相似文献
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铁磁材料因力学性能良好而被各工业领域广泛应用.由于其所处的工作环境和所承受的工作载荷极其复杂,使得铁磁材料构件经常产生应力集中和微裂纹.金属磁记忆检测技术因能够准确检测构件应力集中和微裂纹部位及有效预防铁磁材料的早期疲劳损伤而被广泛关注.然而,由于金属磁记忆检测技术发展时间较短,对应力集中和微缺陷部位还不能实现定量检测.因此,近年来为如何实现金属磁记忆检测技术的定量检测,学者们对材料疲劳损伤在检测中所呈现的磁记忆特征、磁记忆检测机理及检测方法进行了深入研究.目前,研究发现铁磁材料应力集中和缺陷部位的磁场强度以及磁场梯度会发生变化.对于磁记忆检测机理,研究者们提出了自有漏磁场、最小能量原理、等效磁场和微观磁化等主要机理.检测方法起初主要通过磁场法向分量过零,切向分量拥有最大值来判断,但该方法容易出现误判.之后研究者们又通过磁场梯度、二维检测等方法进行判断,极大提高了检测的准确性.本文归纳了金属磁记忆疲劳损伤检测的研究进展,分别对铁磁材料疲劳损伤在检测中的磁记忆特征、金属磁记忆检测机理、金属磁记忆检测铁磁材料疲劳损伤的方法等进行了介绍,分析了金属磁记忆疲劳损伤检测技术面临的问题并对其前景进行了展望,以期为实现金属磁记忆疲劳损伤定量化检测提供参考. 相似文献
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采用射频磁控溅射方法制备非晶DyFeCo磁光薄膜。样品的克尔回线、转矩曲线的测试显示,薄膜具有优良的磁和磁光性能。退火研究表明,随着退火时间的增加,矫顽力下降,垂直磁各向异性能减少,但克尔角变化不明显,其内在机制与薄膜中的微缺陷和应力的弛豫过程有关。 相似文献
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飞机发动机叶片由于工作条件恶劣,容易出现疲劳和微缺陷,采用传统的检测方法难以对它们进行准确检测.针对装备复杂结构微损伤的检测问题,论文提出了一种基于柔性电磁传感器和数字锁定检测算法的微缺陷检测技术,在分析柔性阵列式电磁传感器特性的基础上,重点对传感器转移阻抗的数字锁定检测方法和检测数据处理方法进行了研究.搭建了检测平台,并通过实验验证了检测效果.实验结果表明,传感器转移阻抗测量幅度测量的重复精度达到0.04%,相位测量的重复精度达到0.02%.通过对传感器转移阻抗幅度和相位变化量的分析,准确地检测出了宽度为0.1mm的微裂纹. 相似文献
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金属磁记忆检测是无损检测领域的新技术,而某些形状构件的应力集中和缺陷不能用该方法检测.为了研究构件形状对磁记检测的影响,计算了处于地磁场中的管道壁内的磁场.结果表明,管道和压力容器等适宜用磁记忆检测. 相似文献
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The magnetic field distribution characteristics of surface cracks with various widths are discussed based on finite element (FEM) results.The crack depth was 0.20 mm ,the width range was from 0.02 to 1.00mm .The results showed that crack width and lift-off( the distance between surface and sensor )will influence singals.Discussed in this paper is the influence of various lift-off parameters on the peak to peak values of the normal component in magnetic flux leakage testing .The effects can be applied to evaluate surface breaking cracks of different widths and depths.An idea is presented to smooth narrow, sharp crack tips using alternating current (AC) field magnetization. 相似文献
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Songling HUANG Luming LI Haiqing YANG Keren SHIDepartment of Electrical Engineering Tsinghua University Beijing China 《材料科学技术学报》2004,20(2):231-232
A key issue, which influences the applications of magnetic flux leakage testing, is defect quantification. There have been many research on the relationship between width, depth and magnetic flux leakage of slot defect. However, the length factor is often ignored. The relationship between characteristics of defect leakage field and defect length was investigated. The magnetic flux leakages of a series of plate specimens with the same width, same depth and different length slot defects were tested under the same magnetizing conditions. Testing results show that defect length is an important parameter needed to consider in quantifying defects. 相似文献
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A New Approach for Restoration of Eddy Current Images 总被引:1,自引:0,他引:1
B. P. C. Rao Baldev Raj T. Jayakumar P. Kalyanasundaram W. Arnold 《Journal of Nondestructive Evaluation》2001,20(2):61-72
Eddy current images of defects are blurred due to convolution of point spread function of eddy current probe with defects. Disturbing variables such as lift-off, surface roughness, and material property variations influence the eddy current images. In order to restore the length, width, depth, and orientation of surface-breaking defects in the presence of disturbing variables, a new and comprehensive approach has been developed. This approach uses artificial neural network and image processing methods. Studies on austenitic steel plates confirm that through this approach it is possible to restore the spatial information of surface-breaking defects of uniform or slowly varying depth and also to form their accurate three-dimensional pictures. This approach is fast as well as amenable for automation. 相似文献
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Xiangdong Gao Chongzhou Lan Deyong You Guohua Li Nanfeng Zhang 《Journal of Nondestructive Evaluation》2017,36(3):55
This paper introduces an innovative Nondestructive testing (NDT) approach by using dynamic magneto-optical imaging (MOI) system to diagnose weld defects. MOI mechanism was explained by Faraday magneto-optical effect and magnetic domain theory. Two Q235 specimen MOI experiments based on excitation of permanent magnet and alternating electromagnet (alternating current driven electromagnet) were performed, thus the feasibility of MOI system for weld defects detection was verified and the relation between alternating magnetic field (AMF) and dynamic MO images was discussed as well. In this research, AMF of welded high-strength steel (HSS) weldment was excited by an alternating electromagnet, and dynamic MO images of HSS seam were acquired for weldment NDT. Finally, a pattern recognition method including three steps was proposed. Dynamic MO images were fused periodically and the features of fused images were extracted by principal component analysis. A classifier based on error back propagation (BP) neural network was established to identify these weld features. It proved that typical weld features such as incomplete penetration, sag, crack and no defect can be classified by the proposed method with an accuracy of 93.5%. 相似文献
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W. Sharatchandra Singh S. V. Sagar Kumar B. Purnachandra Rao P. Ravindar 《Research in Nondestructive Evaluation》2013,24(5):253-268
ABSTRACTFor enhanced detection of flaws in engineering components using magnetic flux leakage (MFL) technique, measurement of the leakage magnetic field components along the three perpendicular directions is beneficial. This article presents the three dimensional-magnetic flux leakage (3D-MFL) modeling and experimental studies carried out on carbon steel plates. Magnetic dipole model has been used for the prediction of MFL signals and images. Sensitivity of the MFL signals peak amplitudes of tangential (HX), circumferential (HY), and normal (HZ) components with respect to flaw length, width, depth and lift-off have been studied. A 3D-GMR sensor has been used for simultaneous measurement of all the three components of leakage magnetic fields from surface flaws in 12 mm thick carbon steel plates. The experimental MFL images have been compared with the model predicted MFL images. The sensor has shown the capability to detect and image 0.9 mm deep surface flaws with a signal to noise ratio of 8 dB. Principal component analysis (PCA)-based image fusion has been performed for fusion of the 3D-MFL images to obtain a geometrical profile of the flaws. Study reveals that 3D-GMR enhances the capability for detection of flaws having irregular geometries. 相似文献
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The application of synthetic focusing for imaging crack-like defects in pipelines using guided waves
Davies J. Cawley P. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2009,56(4):759-771
This paper deals with quantifying the performance of a technique for detection, location, and sizing of circumferential crack-like defects in pipelines using synthetically focused guided waves. The system employs a circumferential array of piezoelectric transducer elements. A torsional probing guided wave is excited using the array, which subsequently interacts with the reflecting features of the pipe, such as defects or weld caps. The recorded backscattered signals are synthetically focused to every point of interest in the pipe wall, to form an image of the reflecting features of the pipe. The defect image amplitude is used to estimate the defect depth, and the full width at half maximum of the defect image circumferential profile is used to estimate the circumferential extent of the defect. The imaging system is tested with data from finite element simulations and from laboratory experiments. It is found that reliable sizing of circumferential cracks in finite element simulations and experiments can be achieved if the circumferential extent of the defect is greater than 1.5 lambdaS, where lambdaS is the shear wavelength at the frequency of inspection. This result is theoretically valid for any pipe size, any axial defect location, and any inspection frequency. Amplitude gains of around 18 dB over an unfocused system have been observed experimentally in an 8-inch pipe with a 9 dB SNR improvement. 相似文献
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Rare-earth iron garnet films with in-plane magnetic anisotropy grown on [111]-oriented substrates are promising for the visualization of magnetic leakage fields in nondestructive evaluation. Such magneto-optical films have to be specifically engineered, and we give an example of this technology. To assess the validity and accuracy of finite-element calculations of a magnetization assembly combined with the physical modeling of the image formation, comparisons between calculated and experimentally obtained magneto-optical images of metal-loss defects have been made. A convincing quantitative agreement is demonstrated. It is shown that both physical and computer modeling techniques allow for a predictive engineering design of the prospective applications and provide greater insight into the method. 相似文献
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Zhong Yunjie Gao Xiaorong Luo Lin Pan Yongdong Qiu Chunrong 《Journal of Nondestructive Evaluation》2017,36(4):70
Laser ultrasonic produces frequencies in the MHz range, enabling high accuracy and a strong ability to detect rail surface defects. This paper mainly studied on the simulation of detecting surface-connected rail defects on 60 kg rails with laser ultrasonic, established the finite element model of laser-excited ultrasonic Rayleigh wave, carried out the simulation, and verified the effectiveness of the technology through experiments. To solve the problem that laser ultrasonic is insensitive to the width of defects in actual detection, and unable to make quantitative detection of defects, this paper established a new model on the basis of improving the original model that has been verified, exciting ultrasonic at the two sides at the same time of a rail with two staggered beams of laser separately to detect irregular scratch defects on rail surface, and two groups of signal data were received through two probes. Each group of data can present the half-profile information of defects, and further form two detection images of the defect. At last, the two detection images were combined into a complete image through image processing. The results of the experiment indicate that the technology studied offers a new method for the effective quantitative detection of surface-connected defects on rail. 相似文献
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Simulation and Analysis of 3-D Magnetic Flux Leakage 总被引:1,自引:0,他引:1
《IEEE transactions on magnetics》2009,45(4):1966-1972
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Polarization microscopes are widely used to image the magnetic domains of a magneto-optical disk and to characterize the birefringence of the disk substrate. For high-resolution imaging, unfortunately, the coupling of the polarization rotation from the Kerr signal, the effect of Fresnel's reflection coefficients, and the substrate birefringence severely deteriorate the image contrast obtained from conventional observations. Here we present the technique of differential polarization microscopy, which replaces the analyzer with a Wollaston prism, for providing better image contrast. Images of a magnetic pattern obtained with both conventional and differential methods are observed for objective lenses that have different numerical apertures and magneto-optical disks with and without a birefringent substrate. The computer simulations and experimental results show that the use of this differential method improves the image contrast and provides excellent tolerance for defects of the optical system. 相似文献