Showing papers on "Eddy-current testing published in 2015"
TL;DR: In this article, the effect of dielectric properties of CFRP carbon rovings on eddy current measurement signal has been investigated and an explanation for that effect is seen in the measurement frequency and the capacitive structure of the carbon RoVings.
Abstract: Eddy current testing is well established for non-destructive testing of electrical conductive materials [1]. The development of radio frequency (RF) eddy current technology with frequency ranges up to 100 MHz made it possible to extend the classical fields of application even towards less conductive materials like CFRP [2] [3](Table 2). It turns out that RF eddy current technology on CFRP generates a growing number of valuable information for comprehensive material diagnostic. Both permittivity and conductivity of CFRP influence the complex impedance measured with RF eddy current devices. The electrical conductivity contains information about fiber texture like orientations, gaps or undulations in a multilayered material. The permittivity characterization influenced by dielectric properties allows the determination of local curing defects on CFRP e.g. hot spots, thermal impacts or polymer degradation. An explanation for that effect is seen in the measurement frequency range and the capacitive structure of the carbon rovings. Using radio wave frequencies for testing, the effect of displacement currents cannot be neglected anymore. The capacitive structures formed by the carbon rovings is supposed to further strengthen the dielectric influences on eddy current measurement signal [3]. This report gives an overview of several realized applications and should be understood as a general introduction of CFRP testing by HF Radio Wave techniques.
137 citations
TL;DR: In this article, a pulsed eddy current testing (PECT) method for electrical conductivity measurement of ferromagnetic metallic materials is proposed, which is based on time-domain analytical solutions to the PECT model and determined the conductivity and permeability via an inverse problem established with calculated and measured values of induced voltage.
Abstract: Pulsed eddy current testing (PECT) method for electrical conductivity measurement of ferromagnetic metallic materials is proposed. Based on time-domain analytical solutions to the PECT model of ferromagnetic plates, the conductivity and permeability are determined via an inverse problem established with the calculated and measured values of induced voltage. PECT method for conductivity measurement is verified by the four-point probe method on three carbon steel plates. In addition, the effects of the amplitude of pulsed excitation current and the lift-off of probe coils on measurement results are studied. PECT is an innovative, non-contacting method with good repeatability for electrical conductivity measurement.
75 citations
TL;DR: In this paper, the suitability of each excitation method with respect to the extraction of defects geometrical features is highlighted. And the authors propose to combine the various excitation signals with image processing to improve the defect detection capability when difficult cases are experienced (such as annealed and small cracks) and to extract more accurate information about the defect's geometric characteristics.
62 citations
TL;DR: In this article, an enhancement in the probes to be used on a new nondestructive testing method with eddy currents induced by velocity was presented, in which a permanent magnet that is attached to a moving carriage creates eddy current in the conductive material to be inspected.
Abstract: This paper presents an enhancement in the probes to be used on a new nondestructive testing method with eddy currents induced by velocity. In this method, a permanent magnet that is attached to a moving carriage creates eddy currents in the conductive material to be inspected. By measuring the opposing magnetic field generated by the eddy currents, it is possible to obtain information regarding the presence of defects. Different magnetic field sensors, such as, differential pick-up coils, giant magneto resistors (GMR) and Hall sensors have been used and compared. A permanent magnet moving above a plate was studied using a numerical model to allow further improvements to be made in the probe. Depending on each sensor's geometry, sensing axis and range, its position and orientation must be strategically chosen in order to increase defect sensitivity. The best probe's position is the one that guarantees the highest sensibility to the defects’ presence.
46 citations
TL;DR: In this paper, the electromagnetic properties of multilayer carbon fiber-reinforced polymer (CF-REINF) have been analyzed using a numerical model to analyze the properties of CF-this paper.
Abstract: Due to the heterogeneous nature and electric anisotropy, it is challenging to establish a numerical model to analyze the electromagnetic properties of multilayer carbon fiber-reinforced polymer (CF...
46 citations
TL;DR: In this article, a model-based inversion method is evaluated in terms of liftoff reduction for metal plate in eddy current testing, and a complex yet accurate procedure is presented to do calibrations of coil parameters before use.
Abstract: Model-based inversion method has been studied extensively for characterization of a metal plate in eddy current testing. However, few reports cover liftoff elimination. In this work, model-based inversion method is evaluated in terms of liftoff reduction. For better inversion accuracy, a complex yet accurate procedure is presented to do calibrations of coil parameters before use. The results from simulations and experiments demonstrate that model-based inversion method has an exceptional ability to compensate influence of large liftoff variations by considering it as an unknown variable to be determined.
45 citations
TL;DR: In this paper, the eddy current pulsed phase thermography (ECPPT) was used for carbon fiber reinforced polymers (CFRPs) evaluation considering volumetric induction heating due to small electrical conductivity, abnormal thermal wave propagation, and Fourier analysis.
Abstract: Anisotropy and inhomogeneity of carbon fiber reinforced polymers (CFRPs) result in that many traditional non-destructive inspection techniques are inapplicable on the delamination evaluation. This letter introduces eddy current pulsed phase thermography (ECPPT) for CFRPs evaluation considering volumetric induction heating due to small electrical conductivity, abnormal thermal wave propagation, and Fourier analysis. The proposed methods were verified through experimental studies under transmission and reflection modes. Using ECPPT, the influence of the non-uniform heating effect and carbon fiber structures can be suppressed, and then delamination detectability can be improved dramatically over eddy current pulsed thermography.
40 citations
TL;DR: The paper presents the mathematical basis of the ECT sensor built by the authors; followed by a finite element analysis; and the results show a strong linear behavior for the analyzed parameters.
Abstract: This paper presents a theoretical and experimental study on the use of Eddy Current Testing (ECT) to evaluate corrosion processes in steel bars used in reinforced concrete structures. The paper presents the mathematical basis of the ECT sensor built by the authors; followed by a finite element analysis. The results obtained in the simulations are compared with those obtained in experimental tests performed by the authors. Effective resistances and inductances; voltage drops and phase angles of wound coil are calculated using both; simulated and experimental data; and demonstrate a strong correlation. The production of samples of corroded steel bars; by using an impressed current technique is also presented. The authors performed experimental tests in the laboratory using handmade sensors; and the corroded samples. In the tests four gauges; with five levels of loss-of-mass references for each one were used. The results are analyzed in the light of the loss-of-mass and show a strong linear behavior for the analyzed parameters. The conclusions emphasize the feasibility of the proposed technique and highlight opportunities for future works.
39 citations
TL;DR: In this article, an axially symmetric E-cored coil with a circular air gap inside the core column located above a two-layered conductive half-space is presented.
Abstract: The problem of an axially symmetric E-cored coil with a circular air gap inside the core column located above a two-layered conductive half-space is presented. The truncated region eigenfunction expansion method is used to derive expressions describing the magnetic vector potential of the filamentary coil. The final expressions for the impedance of the rectangular cross-sectional coil are obtained, and calculations for various frequency values are carried out. The results are compared with those from the COMSOL package, which shows a very good agreement.
37 citations
TL;DR: In this article, a pulsed eddy current (PEC) testing signal processing method for ferromagnetic material is presented, without any filtering process that may produce signal distortion, the numerical cumulative integration of the noisy PEC signal is calculated and subsequently fitted to the theoretical model.
Abstract: A pulsed eddy current (PEC) testing signal processing method for ferromagnetic material is presented. Without any filtering process that may produce signal distortion, the numerical cumulative integration of the noisy PEC signal is calculated and subsequently fitted to the theoretical model. The model parameter estimation is later applied to quantify the specimen thickness and reconstruct a denoised PEC signal. A comparison is made between the presented method and the former direct-fitting method. The results demonstrate that the presented method improves the testing performance in terms of the detectable thickness range, the probe lift-off distance, and the measuring time.
27 citations
TL;DR: In this paper, a transceiver transceiver with three identical windings located 120° apart on the same physical axis is proposed to estimate the position of a defect by analyzing the amplitude and phase of the sum of the three terminal voltage signals.
Abstract: Metallic tube inspection techniques using eddy current probes have evolved over the years from those employing a single bobbin coil to rotating coils and arrays, in an attempt to improve the speed and reliability of inspection. This paper presents a novel eddy current transceiver probe design that uses a rotating electromagnetic field. The transceiver coils consist of three identical windings located 120° apart on the same physical axis. A three-phase sinusoidal current source is used for exciting the coils. The phase voltages are identical in amplitude, but 120° apart in phase. The rotating magnetic field generated by the three-phase current is sinusoidal in space and time and so are the induced eddy currents in the tube wall. The sensor achieves mechanical rotating probe functionality by electronic means and eliminates the need for mechanical rotation. The terminal voltages of the three-phase windings can be measured during the scan. The defect’s axial and angular position can be estimated by analyzing the amplitude and phase of the sum of the three terminal voltage signals. The probe is sensitive to defects of all orientations and is as effective as conventional rotating pancake coil probes while offering the advantages of high inspection speed and greater reliability, since the probe does not rotate mechanically. A 3-D finite-element model based on reduced magnetic vector potential Ar, $ {V}$ -Ar formulation was developed to simulate and predict the response of the probe to a variety of defects. A prototype unit consisting of a probe connected to a three-phase constant current source and data acquisition system was developed and tested. Experimental results validating the simulation model and demonstrating the feasibility concept are presented.
TL;DR: In this article, the authors presented novel solutions that correctly incorporate all electromagnetic interactions arising in inductively coupled circuits for the case of a coaxial driver and pickup coil probe encircling a long ferromagnetic conducting rod.
Abstract: Novel solutions that correctly incorporate all electromagnetic interactions arising in inductively coupled circuits are presented for the case of a coaxial driver and pickup coil probe encircling a long ferromagnetic conducting rod. The differential circuit equations are formulated in terms of the rod׳s impulse response using convolution theory, and solved by Fourier transform. The solutions presented here are the first to account for feedback between a ferromagnetic conductor and the driver and pickup coils, providing correct voltage response of the coils. Experimental results, obtained for the case of square wave excitation, are in excellent agreement with the analytical equations.
TL;DR: In this article, the relative variation of magnetic flux is proposed as a feature for the measurement of lift-off and how to directly obtain the key parameters of the feature from the testing signals is provided.
Abstract: Measurement of lift-off can be used to assess the thermal insulation thickness and it has the potential to reduce the lift-off effect in pulsed eddy current testing. In this paper, first, the relative variation of magnetic flux is proposed as a feature for the measurement of lift-off. And then, how to directly obtain the key parameters of the feature from the testing signals is provided. At last, the validity of the feature is verified by simulations and experiments, respectively. The results show that the feature is suitable when the lift-off is tens of millimeters and the plate is ferromagnetic.
TL;DR: This paper provides precision surface data as well as details on the evaluation of the critical parameters of the problem and cross validated the experimental data using a model that combines an integral formulation and the FEM approach.
Abstract: We report on further measurements and a numerical solution for a proposed benchmark problem involving an eddy-current nondestructive evaluation configuration. This is a simplified version of the inspection of fastener holes in aircraft structures, comprising combinations of plates with through holes and a crack. Previously, only line (B-scan) data were provided for the coil impedance, while in this paper, we provide precision surface (C-scan) data as well as details on the evaluation of the critical parameters of the problem. Furthermore, the experimental data are cross validated with numerical ones using a model that combines an integral formulation and the FEM approach.
TL;DR: In this article, a Hall effect sensor is used to measure the magnetic field generated by the induced eddy currents induced by the permanent magnet motion, which is measured in order to detect defects.
TL;DR: The proposed procedure provides a highly adaptive optimization strategy in the framework of LET and proposes new magnet systems with inherently improved characteristics that outperforms currently available cylindrical magnets in terms of weight and performance.
Abstract: We propose a procedure to determine optimal magnet systems in the framework of the nondestructive evaluation technique Lorentz force eddy-current testing (LET). The underlying optimization problem is clearly defined considering the problem specificity of nondestructive testing scenarios. The quantities involved are classified as design variables, and system and scaling parameters to provide a high level of generality. The objective function is defined as the absolute defect response signal (ADS) of the Lorentz force resulting from an inclusion inside the object under test. Associated constraints are defined according to the applied force sensor technology. A numerical procedure based on the finite-element method is proposed to evaluate the nonlinear objective and constraint functions, and the method of sequential quadratic programming is applied to determine unconstrained and constrained optimal magnet designs. Consequently, we propose a new magnet design based on the Halbach principle in combination with high saturation magnetization iron–cobalt alloys. The proposed magnet system outperforms currently available cylindrical magnets in terms of weight and performance. The corresponding defect response signal is increased up to 180% in the case of small defects located close to the surface of the specimen. The combination of active and passive magnetic materials provides an increase of the ADS by 15% compared with the magnet designs that are built solely from permanent magnet material. The proposed procedure provides a highly adaptive optimization strategy in the framework of LET and proposes new magnet systems with inherently improved characteristics.
TL;DR: In this article, the electromagnetic characteristics of biorthogonal rectangular probes were analyzed through finite element simulation and the detection capability of probes according to flaw's width, length and depth were also studied.
TL;DR: In this paper, a variable pulse width excitation was proposed for quantifying the wall thickness of the ferromagnetic specimen, based on the excitation, the slope that the relative increment of magnetic flux linear decays with the increase of pulse width in the semi-logarithmic domain was found.
Abstract: Pulsed eddy current testing (PECT) is a rapidly developing technology which has wide potential applications. For the PECT system which uses detection coils, a no-reference-needed and more efficient method, for quantifying the wall thickness of the ferromagnetic specimen, should be found. In this paper, a kind of variable pulse width excitation is proposed. Based on the excitation, the slope that the relative increment of magnetic flux linear decays with the increase of pulse width in the semi-logarithmic domain is found to be an effective and no-reference-needed feature. First, the analytical expression for the relative increment of magnetic flux is presented, and the validity of the feature is verified by experiments. Then the potential factors affecting the feature are investigated in detail. Results show that when the electromagnetic properties of the specimen are invariant, the feature is independent of pulse width parameters, analysis interval and coatings thickness. At last, a quantitative method is demonstrated. More time could be saved for the narrow pulse comparing it with the existing excitations, and the feature could widely meet engineering applications.
TL;DR: In this paper, a new eddy current method named induction heating assisted EDD current testing (IHAET) was proposed for detecting delamination in thermoplastic CFRP welded zones.
Abstract: This paper presents a new eddy current method named induction heating assisted eddy current testing (IHAET) for detecting delamination in thermoplastic CFRP welded zones. In IHAET, weld part is heated by induction heating to produce a high temperature spot on delamination. Electrical conductivity of the high temperature spot is larger than that of intact zones due to temperature dependence of conductivity of carbon fibers and its location can be identified by multiple pickup coils. Experimental studies carried out on CF fabric/PPS showed the validity of IHAET and detected 450 mm2 delamination 2 mm away from the surface by using a statistical diagnosis.
TL;DR: Results show the capability of neural network data fusion to improve stress measurement accuracy and the accuracy of fused data are compared with PEC and UT information.
Abstract: Stress and residual stress are two crucial factors which play important roles in mechanical performance of materials, including fatigue and creep, hence measuring them is highly in demand. Pulse eddy current (PEC) and ultrasonic testing (UT) are two non-destructive tests (NDT) which are nominated to measure stresses and residual stresses by numerous scholars. However, both techniques suffer from lack of accuracy and reliability. One technique to tackle these challenges is data fusion, which has numerous approaches. This study introduces a promising one called neural network data fusion, which shows effective performance. First, stresses are simulated in an aluminium alloy 2024 specimen and then PEC and UT signals related to stresses are acquired and processed. Afterward, useful information obtained is fused using artificial neural network procedure and stresses are estimated by fused data. Finally, the accuracy of fused data are compared with PEC and UT information and results show the capability of neural network data fusion to improve stress measurement accuracy.
TL;DR: In this paper, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on a carbon steel plate, and the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness.
Abstract: To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters, it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate.
11 May 2015
TL;DR: This work presents a method to detect sub-surface defects in non-ferromagnetic material with motion induced eddy currents, using a numerical model to verify the progression of eddy current along the depth of a conductive plate and to obtain the magnetic field perturbation in the presence of sub- surface defects.
Abstract: Nondestructive testing in situations where there is a moving media has always been a challenging task. Motion induced eddy current testing is a good solution for testing metallic surfaces, as it does not require contact with the sample. This work presents a method to detect sub-surface defects in non-ferromagnetic material with motion induced eddy currents. A numerical model was used to verify the progression of eddy currents along the depth of a conductive plate and to obtain the magnetic field perturbation in the presence of sub-surface defects. A probe, including a permanent magnet to induce eddy currents and a magnetic sensor was moved in the vicinity of an aluminium plate with sub-surface defects to obtain experimental data and the results compared to those obtained with the numerical model. At higher speeds, the time of diffusion of deeper eddy currents takes, makes it possible to also estimate the depth of a sub-surface defect by measuring how far away the perturbation is from the moving magnet.
TL;DR: In this paper, an eddy current testing probe for inspection of non-conductive glass fiber reinforced plastics is proposed, where the magnetic field contains information pertaining to the permittivity of materials under test.
Abstract: This paper presents the design of an eddy current testing probe for inspection of non-conductive glass fiber reinforced plastics Because the magnetic field contains information pertaining to the permittivity of materials under test, eddy current testing offers the possibility of flaw detection in non-conductive materials through detection of the difference in permittivity between the intact part and the defective part of each material We analytically investigated the design of a probe suitable for dielectric constant measurements Experimental studies proved that the proposed probe can detect slit defects and flat-bottomed holes located 2 mm away from the surface of the glass fiber reinforced plastic samples
20 Jan 2015
TL;DR: In this article, a modified eddy current testing method based on the use of miniature EDD current transducers within a localized controlled area of the material surface of up to 50 7 μm2 was proposed.
Abstract: The paper puts forward a modified eddy current testing method based on the use of miniature eddy current transducers within a localized controlled area of the material surface of up to 50 7 μm2. Measurement results are provided for a model composite material made up of alternating conducting and dielectric layers of system Al-PAPER-Al. Structural flaws are specified as changes in the number and position of layers in the sequence. Prospects of the proposed method and a measuring device operating on its basis for flaw detection in composite aluminum alloy materials are shown.
TL;DR: The problem is resolved by dividing the solution domain into subdomains, and the proposed method has the merits of easy mesh generation and efficient and accurate solution.
Abstract: A typical eddy-current testing (ECT) process involves scanning of conducting test sample using an EC probe, which can be an air-core coil or ferrite-core coil. Its accurate and efficient modeling is critical to probe and testing parameter optimization. The finite-element method (FEM) has been widely used in ECT simulation. Unfortunately, the conventional FEM is cumbersome and inefficient when the movement of a ferrite-core coil is to be considered, because the change of the coil position results in repetition of meshing as well as generating and preconditioning matrix equation. In this paper, we resolve the problem by dividing the solution domain into subdomains. The test sample and the ferrite core are assigned to different subdomains, and each subdomain is meshed independently. The excitation coil is not included in a subdomain, and its contributions to the magnetic fields in both subdomains are calculated analytically. Solutions of the subdomains are coupled by calculating the contribution of the induced current or magnetization current in a subdomain to the magnetic field in the other subdomain. The proposed method has the merits of easy mesh generation and efficient and accurate solution.
TL;DR: In this article, an inspection system is designed to detect inner wall flaws in pipe based on pulsed eddy current technique, which can detect 10 percent thinning of wall under insulation when the thickness of pipe and insulation is respectively 10mm and 110mm.
TL;DR: In this article, a solution for the case of a driver coil encircling a ferromagnetic conducting rod is presented, where the differential circuit equation is formulated in terms of the rod's impulse response using convolution theory, and solved by Fourier transform.
Abstract: A solution is presented for the case of a driver coil encircling a ferromagnetic conducting rod. The differential circuit equation is formulated in terms of the rod׳s impulse response using convolution theory, and solved by Fourier transform. The final solution accounts for feedback between the ferromagnetic rod and the driver coil, providing correct voltage response of the coil. Also arising from the solution is an analytical expression for the complex inductance in the circuit, which accounts for real (inductive) and imaginary (loss) elements associated with the rod. Experimental results, obtained for the case of square wave excitation, show excellent agreement.
TL;DR: In this article, the authors provided insight into eddy current models for stratified conductive structures using three types of analytical approaches, including Cheng's matrix method, Truncated region eigenfunction expansion (TREE) method, and the innovative method based on the reflection and transmission theory of the electromagnetic waves.
Abstract: The excitation and propagation of an electromagnetic field is a very complex problem in Stratified conductive structures (SCS) because of their complicated physical properties. In single air-cored coil above multilayered conductive structures, the impedance of an eddy-current coil is calculated based on the electromagnetic field. This paper provides insight into eddy current models for stratified conductive structures using three types of analytical approaches, including Cheng’s matrix method, Truncated region eigenfunction expansion (TREE) method, and the innovative method based on the reflection and transmission theory of the electromagnetic waves. The analytical expressions of the three models are discussed and compared. Numerical simulation of an FEM model is performed, and the experimental results verify the developed models.
01 Jan 2015
TL;DR: In this article, the authors presented measurements using MR array probes consisting of 32 TMR-elements (tunnel magneto resistance), an ASIC, and subsequent readout components.
Abstract: Magneto-resistive (MR) sensor arrays are suited for high resolution eddy current testing (ET) of aerospace components due to two significant advantages compared to conventional coil systems. First, to obtain high spatial resolution they can be manufactured down to the µm-regime without losing their outstanding field sensitivity. Secondly, MR technology has a relatively frequency-independent sensitivity in the range of common ET-frequencies thus providing a benefit for low frequency applications.
This paper presents measurements using MR array probes consisting of 32 TMR-elements (tunnel magneto resistance), an ASIC, and subsequent readout components. A source for generating the eddy currents inside the material under test is also implemented onboard of the PCB. These probes were developed in the IMAGIC-project* for detection and imaging of surface breaking defects.
The performance of the new sensor system has been investigated for several mock-ups, Aluminum and Titanium plate specimens having small adjacent boreholes with diameter of 0.44 mm and micro notches in the µm-range, respectively. To compare our results we used conventional eddy current probes. The MR sensor elements have a length of around 60 µm leading to a nearly 'point like' measurement. Neighbouring boreholes (depth 0.25 mm) with a separation of 0.6 mm between their centres could be resolved with a good SNR, and more important, the boreholes could be confidently distinguished using the TMR-probes. In case of conventional probes a reliable separation was not possible. In this paper we present the MR-ET-probes of the IMAGIC consortium and a comparison with conventional techniques.
*The IMAGIC-project ('Integrated Magnetic imagery based on spIntronics Components', 2011 – 2014, project reference: 288381) was funded by the European Commission, Seventh Framework Programme. Further partners involved in the consortium beside BAM and CEA were INESC-ID and INESC-MN (Portugal), Sensitec GmbH (Germany), Tecnatom S.A. (Spain), and Airbus Group (France).