摘要:

Previous work on the detection of cracks around fastener holes in multi‐layer structures using eddy current NDE has met with some success; however, challenges remain in detecting smaller corner cracks while minimizing false call rates. To address this issue, a 3D model was developed for this problem and successfully validated with experimental data. Using this model, a series of numerical studies were performed to identify potential features for defect classification. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711642

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The interpretation of eddy current testing (ECT) signals is known as a truly difficult task since it is influenced by various factors including the variation in geometry and material properties of steam generator tubes. To provide necessary information for the proper signal interpretation, the present study investigates the behavior of bobbin‐coil ECT signal according to the changes in diameter, electric conductivity and magnetic permeability of a tube using a 2‐dimensional finite element analysis program. It was found that the behaviors of a differential bobbin coil probe were similar to those of an absolute bobbin coil probe for localized variation. However, quite different behaviors were observed for two probes for the cases of smooth variation in geometry. It was also found that the phase angle of ECT signals could be used as an effective feature to identify the kind of abnormalities. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711643

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Eddy current carries electric charges, some which are accumulated as induction charges around a discontinuity. The induction charges develop electric potential because they repel one another based on Coulomb’s force. This paper indicates that eddy current is induced not only by induction electric field but also by gradient of the electric potential. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711644

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In light of its frequency‐dependent penetration depth, the measurement of eddy current conductivity has been suggested as a possible means to allow the nondestructive evaluation of subsurface residual stresses in surface‐treated specimens. Unfortunately, the relatively small change in electrical conductivity caused by the treatment is often accompanied by an apparent conductivity loss caused by the spurious surface roughness. This paper investigates the apparent reduction of the near‐surface electrical conductivity measured by the eddy current method in the presence of surface roughness. The rough surface is modeled as a one‐dimensional sinusoidal corrugation using the Rayleigh‐Fourier method. The apparent conductivity is determined from the resulting change in the plane‐wave reflection coefficient of the conducting half‐space at normal incidence. In spite of the simplicity of the suggested analytical model, the obtained theoretical results are found to be in good qualitative agreement with recently published experimental data on shot‐peened copper specimens. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711645

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

There has been a growing need in the electric utility industry to assess the remaining life of blades in gas turbines. It is quite important to nondestructively comprehend the depths of surface‐breaking cracks in blades. Flexible eddy current array probes have been developed to overcome the major limitations of existing eddy current inspection systems. The use of an array of sensors allows cracks of all lengths to be detected and will ultimately allow real time data imaging to provide rapid inspection and easy interpretation. For this study using eddy current techniques, crack detection equipment has been developed and applied to gas turbine Stage 1 blades for field use. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711646

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The eddy‐current testing technique gives a new skill for inspection of bare printed circuit board (PCB). The combination of the high‐sensitive micro eddy‐current testing (ECT) probe and the image processing technique enables us to inspect defect (disconnection, and chipping crack) on the trace of bare PCB. This paper deals with the structure of the probe and characteristics to apply the ECT approach to the inspection of high‐density PCB. We proposed the ECT probes of the meander coil (transmitter) and Spin‐Valve Giant Magnetoresistance sensor(receiver). The high frequency excitation up to 5 MHz enables us to detect the disconnection on the trace of less than 100 &mgr;m width and 35 &mgr;m thickness. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711647

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this paper authors propose an eddy current probe, which is suitable for inspection of low conductivity structures. The probe consists of an excitation coil and two differentially connected search coils. The detection circuit was designed in this way that a resonance for an operating frequency was obtained. It creates possibility to achieve a high sensitivity of the measuring system. The transducer was used to examine heterogeneities of low conductivity specimens. The test specimens consist of various plexiglass elements placed into a tank filled with drinking water or water solution of NaCl. Results of measurements confirm usability of the sensor and the whole measuring system. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711648

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This compares the capabilities of the Pulsed Eddy Current technique with those of an Eddy Current instrument capable of multiplexing through 32 discrete frequencies. Pulsed Eddy Current testing has shown some definite advantages due to the application of an extended series of frequencies to a test piece and analysis using a time‐based display. The Eddy Current equipment allows high energy drive and wide dynamic signal range within each of 32 individual timeslots. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711649

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Rotational and linearly scanned eddy current probes based on giant magnetoresistive (GMR) sensors have been developed for detecting buried cracks and flaws emanating from fastener holes. The use of shaped excitation coils, the original positioning and orientation of the magnetic sensors enhance the sensitivity of these probes to buried defects while reducing the influence of fastener holes edge. Corner cracks of 2.5 mm in length were detected in the second layer of a 13 mm thick two‐layer structure. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711650

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The advent of GMR magnetic sensors and GMR sensor arrays with frequency‐independent sensitivity offers improvements in speed, depth, and resolution in eddy‐current testing. Arrays of GMR magnetic sensors allow rapid scanning of an area for defects in a single pass. The small size and low power consumption of these solid‐state magnetic sensors enable the fabrication of compact arrays of sensors on circuit boards and even on‐chip sensor arrays. Arrays have been fabricated with sensor spacing as small as 5 micrometers when fine resolution is required. GMR sensor elements can be deposited on active silicon substrates facilitating on‐chip signal processing and multiplexing. This integration simplifies the sensor/signal‐processing interface, minimizes the number of leads, and can reduce the effect of noise. This paper will discuss the technology of fabricating arrays on GMR sensors, especially on‐chip arrays. Integrated sensor arrays with on‐chip signal processing and multiplexing will be described. Finally, some applications of arrays to crack and corrosion detection will be discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1711651

出版商:AIP    

年代:1904

数据来源: AIP