Showing papers on "Eddy-current testing published in 1990"
TL;DR: In this article, the authors give a guideline to the literature of magnetic methods for nondestructive evaluation of materials for flaws and defects, including magnetic particle inspection, magnetic flux leakage, leakage field calculations and eddy current inspection.
Abstract: This paper gives a guideline to the literature of magnetic methods for nondestructive evaluation of materials for flaws and defects. This is a sequel to an earlier paper which described magnetic methods for nondestructive evaluation of stress, plastic deformation and microstructure. The present paper discusses magnetic particle inspection, magnetic flux leakage, leakage field calculations and eddy current inspection, including the remote field electromagnetic inspection method. An extensive survey of recent publications in the field is given.
108 citations
Journal Article•
TL;DR: In this article, the use of neural networks for interpreting signals from eddy current probes used in nondestructive testing (NDT) is proposed, and classification results obtained by implementing a multilayered neural network using the back-propagation algorithm are presented.
Abstract: This paper proposes the use of neural networks for interpreting signals from eddy current probes used in nondestructive testing (NDT). Classification results obtained by implementing a multilayered neural network using the back-propagation algorithm are presented. The merits of this approach as well as a comparison with traditional techniques for the classification of signals are also discussed
74 citations
TL;DR: In this article, the quantitative relations between the true depth of penetration and the standard depth-of-penetration (DOP) are presented for three configurations of eddy current probe and test material.
Abstract: The true depth of penetration of eddy currents generated in a conducting sample by an air-cored probe coil, besides depending on the electromagnetic wave frequency and the magnetic permeability and electrical conductivity of the sample, also depends strongly on the coil dimensions and the sample thickness. The standard depth of penetration widely used as a guide for eddy current inspection purposes is calculated for a plane electromagnetic wave incident perpendicularly on a conducting half-space and is thus a material/test parameter rather than a true measure of penetration. In this paper the quantitative relations between true depth of penetration and standard depth of penetration are presented for three configurations of eddy current probe and test material. First an air-cored coil above a conducting half-space is considered, then the same coil above a conducting sheet, and finally the true depth of penetration is calculated in a conducting half-space covered with cladding for different ratios of condictivity between cladding and base material.
57 citations
TL;DR: In this paper, a general-purpose hybrid finite element and finite difference computational model was developed for the prediction of pulsed eddy-current distribution in metals for nondestructive testing purposes.
Abstract: A general-purpose hybrid finite-element and finite-difference computational model developed for the prediction of pulsed eddy-current distribution in metals for nondestructive testing purposes is discussed. The numerical model uses an axisymmetric formulation to study coil configurations suspended over a metallic specimen. As a driving function, a pulsed Maxwell-distributed current density is applied. Resulting eddy-current distributions are discussed as a function of conductivity, permeability, and lift-off. The transition voltage response of a coil over an infinite half-space is numerically computed and compared to the solution obtained by a novel analytical approach. The numerical model is then used to determine the induced voltage due to a surface-breaking flaw. >
39 citations
Journal Article•
26 citations
TL;DR: In this article, a computational model was developed for the simulation of eddy-current nondestructive testing, where the electric field produced by a probe in the absence of the flaw was determined; then the field induced at the flaw is found.
Abstract: A computational model has been developed for the simulation of eddy-current nondestructive testing. The electric field produced by a probe in the absence of the flaw is determined; then the field induced at the flaw is found. These field calculations are based on volume integral techniques requiring only the region of the scatterer to be discretized. Boundary conditions at infinity and interface conditions at the surface of the conductor are built into the Green's function kernels, thus ensuring that the scattered field satisfies these conditions. The discrete equations are formed using the method of moments and solved using conjugate gradient methods. The proposed model was applied to the calculation of the interaction of two ferrite core eddy-current probes with five simulated EDM notches in a material of conductivity 1.2% IACS, at a frequency of 2 MHz. The results obtained confirm the validity of the proposed method. >
20 citations
Patent•
10 Sep 1990
TL;DR: In this article, a non-contact eddy current inspection system provides compensation for variations in the distance between the probe and the workpiece surface by using vector analysis of the signals through inductive coils.
Abstract: A non-contact eddy current inspection system provides for compensation for variations in the distance between the eddy current probe and the workpiece surface. Probe height from the surface is first determined for a scan using a vector analysis of the signals through inductive coils. Height compensated data signals are then compared against a threshold value to determine the presence of flaws in a workpiece surface.
20 citations
TL;DR: In this paper, it was shown that the eddy currents in a specimen affect the measurement error of the SST, and the error increases with increase in the overhang length and with decrease in the distance between yokes.
Abstract: The most favorable construction of the yoke of a single-sheet tester (SST) has been studied by measurements and numerical analysis. It is shown that the eddy currents in a specimen affect the measurement error of the SST, and the error increases with increase in the overhang length and with decrease in the distance between yokes. It is concluded that the single-yoke-type tester has a large error due to eddy currents and that the double-yoke tester is superior. If a single-yoke-type SST is used, the lengths of the B and H coils should be chosen in such a way that the measured power loss is not affected by the eddy currents in the specimen. >
19 citations
TL;DR: In this article, a theoretical model is presented to describe the time-harmonic induction of eddy currents in a layered conductor containing a crack, and explicit expressions for the magnetic vector potential in the absence of the crack are derived for the particular case of induction by a circular aircored coil, and these results are used to calculate the change in coil impedance ΔZU due to the induced currents in the uncracked system.
Abstract: A theoretical model is presented to describe the time‐harmonic induction of eddy currents in a layered conductor containing a crack. The layered system consists of two parallel conducting plates separated by an insulating gap and it is assumed that the thickness tS of the plate containing the (through‐the‐thickness) crack is small compared with the electromagnetic skin depth δS. Explicit expressions for the magnetic vector potential in the absence of the crack are derived for the particular case of induction by a circular air‐cored coil, and these results are used to calculate the change in coil impedance ΔZU due to the induced currents in the uncracked system. The effect of a through‐the‐thickness crack is represented by an equivalent distribution of current sources along the line of the crack. The form of these generalized current vortex sources is examined and explicit expressions are presented for the current density and vector potential due to a single vortex. The vortex density, and hence the induced current distribution, are obtained by solving a one‐dimensional singular integral equation. This formalism is used to calculate the change in coil impedance ΔZC due to a first‐ or second‐layer crack. Experimental measurements of ΔZ were carried out for several model systems and the theoretical calculations were found to agree with experiment to within 10% or better for tS/δS up to 0.4. The implications for the detectability of cracks using eddy‐current nondestructive inspection is discussed.
12 citations
Journal Article•
TL;DR: In this paper, the use of a differential transformer-type magnetic sensor for nondestructive testing was simulated by boundary element analysis, taking the external electric secondary circuit, the eddy currents, and movements into account.
Abstract: The use of a differential transformer-type magnetic sensor for nondestructive testing was simulated by boundary element analysis, taking the external electric secondary circuit, the eddy currents, and movements into account. The existence of an error caused by the narrow air gap is identified, an element subdivision method is proposed for decreasing the error, and this method is shown to be effective. The analytical results are shown to be in good agreement with the measurement results. It is shown that the output voltage pattern can be used to estimate the shape or size of a flaw. >
TL;DR: In this paper, a zoom-in technique for 3D electromagnetic field calculation to 3D remote field eddy current effect computation is introduced, which is especially suitable for problems that are essentially two-dimensional but with some local 3D character.
Abstract: A novel application of the zoom-in technique for 3-D electromagnetic field calculation to 3-D remote field eddy current effect computation is introduced. The technique is especially suitable for problems that are essentially two-dimensional but with some local 3-D character. Significant reduction of computer resources is achieved by using this technique, since only a small portion of the whole calculation region, basically the 'three-dimensional part' of the problem, is under consideration. Some data from the solution of the corresponding two-dimensional or axisymmetrical problem are used as the boundary condition of the 3-D problem in computation. The validity of the method has been verified by a comparison of its results with those from an axisymmetric problem. >
TL;DR: In this paper, the authors investigated the sensitivity of the eddy-current measuring system as a function of the various parameters by numerical simulations, and presented a suitable measuring environment for nondestructive testing of the properties of materials.
Abstract: Finite-element methods employing voltage sources rather than widely used current sources are used to evaluate magnetic permeability, impedance, and transformed fraction in metals. The transformed fractions have been successfully estimated by nondestructive eddy-current measurements using voltage sources. The experimental results agree well with those of numerical simulations. The authors also investigate the sensitivity of the eddy-current measuring system as a function of the various parameters by numerical simulations, and present a suitable measuring environment for nondestructive testing of the properties of materials. It is determined that a rectangular sensor may be better than a cylindrical sensor in eddy-current measurements of conductive material. >
01 Jan 1990
TL;DR: In this article, the use of the comparison of phase and amplitude data from two probe frequencies to distinguish cracks from changes in local magnetic permeability was explored, which can be used to detect cracks.
Abstract: Single frequency phase analysis eddy current techniques have limited potential for inspections for surface cracking in inhomogeneous ferromagnetic welded surfaces [1). Signals from these cracks are masked in noise produced by lift-off, probe wobble and local changes of the permeability of the weld, the most troublesome noise source. Surface cracks and changes in magnetic permeability create signals with phase angles that are too close to be discriminated from each other. Another method, in addition to phase discrimination, must be used to distinguish crack signals from signals created by changes in magnetic permeability. This paper explores the use of the comparison of phase and amplitude data from two probe frequencies to distinguish cracks from changes in local magnetic permeability.
TL;DR: In this paper, the double yoke single sheet tester is recommended for use as a standard tester, because the eddy current distributions on the surfaces of the two sides of the specimen are different from each other when a single yoke tester was used.
Abstract: Iron losses measured by a single sheet tester depend on the construction of the yoke. The reason for this is examined through measurement and numerical analysis. The double yoke single sheet tester is recommended for use as a standard tester, because the eddy current distributions on the surfaces of the two sides of the specimen are different from each other when a single yoke tester is used.
TL;DR: A modified open-boundary technique that allows the unbounded region exterior to an axisymmetric problem region to be mapped into second coaxial cylindrical region connected over its surface to the first region is described in this paper.
Abstract: A modified open-boundary technique that allows the unbounded region exterior to an axisymmetric problem region to be mapped into second coaxial cylindrical region connected over its surface to the first region is described. A comparative example of the use of the technique to model the performance of a remote-field eddy-current tool is given. It is found that the advantages of the open-boundary technique are reduced time to construct the simpler mesh, which may save several weeks of testing, and the improved accuracy of the solution when compared with results obtained using a restricted exterior region. >
TL;DR: In this article, the electromagnetic energy flow is studied to elucidate the phenomena underlying remote-field eddy-current nondestructive testing of magnetic tubes, and the flow intensity as well as its direction is obtained quantitatively.
Abstract: The electromagnetic energy flow is studied to elucidate the phenomena underlying remote-field eddy-current nondestructive testing of magnetic tubes. The flow intensity as well as its direction is obtained quantitatively. The energy travels through the tube wall from the outside into the inside of the tube in the remote field area, carrying the information on the tube wall thickness. This makes it possible to use this method to detect defects in ferromagnetic tubes. >
01 Jan 1990
TL;DR: In the design of an inspection device, it is useful to have available a means of visualizing the eddy current distribution produced in the material to be tested as discussed by the authors, and this is evidenced by the widespread use of the early models of Dodd and Deeds [1], who provided analytic solutions for the field in a number of axisymmetric probe geometries.
Abstract: In the design of an eddy current inspection device, it is useful to have available a means of visualizing the eddy current distribution produced in the material to be tested. This is evidenced by the widespread use of the early models of Dodd and Deeds [1], who provided analytic solutions for the field in a number of axisymmetric probe geometries. The analytic approach was later extended [2–4] to include a more general class of coils, and was applied to the case of a circular, air-core horizontal coil [4].
TL;DR: In this article, a volume element calculation was used to predict the field at the slot in a conductor excited by an eddy current probe, where the slot simulates the presence of a surface crack in a metal component.
Abstract: A volume element calculation has been used to predict the field at the slot in a conductor excited by an eddy current probe. The slot simulates the presence of a surface crack in a metal component. Interaction between the simulated flaw and the electromagnetic field is computed in order to model the fundamental physical process of eddy-current nondestructive evaluation. The results are used to suggest methods for improving testing techniques and to develop procedures for processing inspection data. As part of an ongoing program to validate the computer model, the authors compare predictions of the volume element calculation with analytical results for a test case. In the test problem, a constant, unidirectional eddy-current distribution is perturbed by a semicircular crack of negligible size at the surface of a half-space conductor. By taking the low-frequency limit, the field at the flaw and the change in probe impedance due to the presence of the flaw are given explicitly by simple analytical expressions. Numerical results found using the volume element calculation are compared with values found from the analysis, and good agreement is found. >
TL;DR: In this paper, the use of 3D eddy current codes to calculate NDT (nondestructive testing) problems is described, and the investigations have been carried out on problem eight of the TEAM Workshops.
Abstract: The use of 3-D eddy current codes to calculate NDT (nondestructive testing) problems is described. The investigations have been carried out on problem eight of the TEAM Workshops. To avoid thin finite-element (FE) sheets in a FE structure so that a well-conditioned equation system is obtained, the possibility of modeling a crack with the aid of boundary conditions is discussed. The field quantities in the vicinity of the crack are compared for the fully modeled crack and for the crack represented by boundary conditions. >
01 Jan 1990
TL;DR: In this article, the performance of an eddy current inspection depends in large part on the performance performance of the eddy-current probe, and consistent performance requires identification of the EDD current probe parameters which characterize performance.
Abstract: The accuracy of an eddy current inspection depends in large part on the performance of the eddy current probe. Consistent performance requires identification of the eddy current probe parameters which characterize performance. These parameters could then serve as a basis for probe procurement specification. Their measurement would also provide a basis for the evaluation of probes which are currently used at inspection facilities and which may have deteriorated[1].
Journal Article•
01 Jan 1990
TL;DR: The measurement system is a precision impedance analyzer capable of measuring impedance or any impedance related quantity over a wide range in frequency and examples of its use to measure flaw signals with a uniform-field eddy current probe are given.
Abstract: We have developed an automated eddy current measurement system in our laboratory for quantitative nondestructive evaluation applications. The heart of the measurement system is a precision impedance analyzer capable of measuring impedance or any impedance related quantity over a wide range in frequency (102–108 Hz). Data acquisition, processing, analysis, and display is accomplished with a personal computer. Computer-controlled x-y positioning stages permit measurements to be obtained for either one- or two-dimensional scans of the specimen. In this article we describe the measurement system and give examples of its use to measure flaw signals with a uniform-field eddy current probe [1].
01 May 1990
TL;DR: An exact theory for the determination of the impedance change of a horizontal-axis eddy-current coil as it is brought close to a conducting homogeneous half space has been extended to consider a layered half space as discussed by the authors.
Abstract: An exact theory for the determination of the impedance change of a horizontal-axis eddy-current coil as it is brought close to a conducting homogeneous half space has been extended to consider a layered half space. The derivation of the theoretical relation for coil impedance change is given and two test cases are considered both experimentally and theoretically. Good agreement is demonstrated between theory and experiment. The possible application of the theory to the study of electromagnetic methods for the nondestructive measurement of the thickness of a layer or coating on a base material is discussed.
01 Jan 1990
TL;DR: In this paper, the T-ω method was proposed for 3D eddy current analysis, where a magnetic scalar potential ω is not included and we do not need variables in space.
Abstract: There are many approaches to 3D eddy current analysis. Typical methods for the eddy current analysis are the A-o method and the T-ω method. Both methods require variables in space as well as in a conductor. We have already proposed the T method [1, 2, 3], where a magnetic scalar potential ω is not included and we do not need variables in space. But the method has a disadvantage that a large core memory is needed due to a dense matrix.
17 Apr 1990
TL;DR: Two theoretical models that exemplify the use of analytical and numerical methods in the interpretation of NDE (nondestructive evaluation) data are reviewed in this article, where an application of a simple analytical model to the eddy current measurement of magnetic permeability, while the second concerns use of the boundary element method for modeling flaw detection in steel pipes.
Abstract: Two theoretical models that exemplify the use of analytical and numerical methods in the interpretation of NDE (nondestructive evaluation) data are reviewed. The first example is an application of a simple analytical model to the eddy current measurement of magnetic permeability, while the second concerns use of the boundary-element method for modeling flaw detection in steel pipes. >
01 Oct 1990
TL;DR: In this paper, the use of E-probes and horseshoe probes for inspecting graphite fiber materials was evaluated and shown to hold great promise once the technology development matures.
Abstract: The recognition of defects in materials properties still presents a number of problems for nondestructive testing in aerospace systems. This project attempts to utilize current capabilities in eddy current instrumentation, artificial intelligence, and robotics in order to provide insight into defining geometrical aspects of flaws in composite materials which are capable of being evaluated using eddy current inspection techniques. The unique capabilities of E-probes and horseshoe probes for inspecting probes for inspecting graphite fiber materials were evaluated and appear to hold great promise once the technology development matures. The initial results are described of modeling eddy current interactions with certain flaws in graphite fiber samples.