Showing papers on "Eddy-current testing published in 2016"
TL;DR: In this paper, a specialized probe was proposed to detect in-plane and out-of-plane fiber waviness in unidirectional carbon fiber-reinforced plastics and to characterize fiber orientations by an eddy current-based nondestructive technique.
Abstract: In this paper, we propose a specialized probe to detect in-plane and out-of-plane fiber waviness in unidirectional carbon fiber-reinforced plastics and to characterize fiber orientations by an eddy current-based nondestructive technique. Experimental studies show that the proposed probe can detect in-plane fiber waviness with amplitude of 1.1 mm and length of 15.9 mm in a thin unidirectional carbon fiber reinforced plastic at sufficiently high drive frequency. The validity of the proposed method is verified through three-dimensional finite element method analysis. Variation in amplitude and phase of output signal obtained in numerical analyses qualitatively agreed with experimental results. Out-of-plane fiber waviness induced in a thick unidirectional carbon fiber-reinforced plastic can also be detected using the proposed probe. It is found that output signals in complex plane obtained during scanning a material with out-of-plane waviness become ring-shaped plots. Those plots in complex plane are used to identify the presence and location of out-of-plane fiber waviness.
93 citations
TL;DR: The structure and principles of GMR sensors, the principles and types of eddy current testing probe that have been studied and developed by previous researchers, and the limitations of coil probe and compensation techniques that researchers have applied in eddyCurrent testing probes are described.
Abstract: Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper.
72 citations
TL;DR: In this article active infrared thermography with microwave excitation is analyzed both by numerical modeling and experiments and should be considered as a preliminary method for the assessment of relatively shallowly located steel bar reinforcements.
Abstract: The purpose of this paper is to present a multi-sensor approach to the detection and inspection of steel bars in reinforced concrete structures. In connection with our past experience related to non-destructive testing of different materials, we propose using two potentially effective methods: active infrared thermography with microwave excitation and the eddy current technique. In this article active infrared thermography with microwave excitation is analyzed both by numerical modeling and experiments. This method, based on thermal imaging, due to its characteriatics should be considered as a preliminary method for the assessment of relatively shallowly located steel bar reinforcements. The eddy current technique, on the other hand, allows for more detailed evaluation and detection of deeply located rebars. In this paper a series of measurement results, together with the initial identification of certain features of steel reinforcement bars will be presented.
60 citations
TL;DR: In this article, a suitable frequency range of swept-frequency eddy current testing is determined by comparing sensitivities of relative reactance change with respect to pipe thickness and other parameters at different frequencies.
Abstract: Swept-frequency eddy current measurement of pipe thickness is studied in this paper. First, suitable frequency range of swept-frequency eddy current testing is determined by comparing sensitivities of relative reactance change with respect to pipe thickness and other parameters at different frequencies. Based on analytical solutions to pipe eddy current field, Levenberg–Marquardt algorithm and variable transformation, a method for solving inverse eddy current problem is developed. Finally, several inversion calculations are carried out and the results are close to the truth values. The low errors reveal that the method presented in this paper is appropriate.
53 citations
TL;DR: In this article, a series of simulations are conducted to analyze the characteristics of gradient field signals and inspection sensitivity to hidden corrosion, and experiments of Gradient-field PEC (GPEC) for evaluation and imaging of hidden corrosion are carried out.
Abstract: Pulsed eddy current testing (PEC) has been found advantageous over other non-destructive evaluation (NDE) techniques particularly in detection and characterization of subsurface defects in conductive structures. The measurement of net magnetic field for acquisition of transient signals is normally employed in traditional PEC during inspection of conductors. In this paper, PEC in conjunction with gradient field measurement is investigated in an effort to enhance the inspection sensitivity to hidden corrosion in conductors and accuracy of corrosion imaging. Closed-form expressions of gradient field and its sensitivity to hidden corrosion are formulated via the extended truncated region eigenfunction expansion (ETREE) modeling. A series of simulations are subsequently conducted to analyze the characteristics of gradient field signals and inspection sensitivity to hidden corrosion. Following this, experiments of Gradient-field PEC (GPEC) for evaluation and imaging of hidden corrosion are carried out. Through theoretical and experimental investigation, it has been found that the GPEC probe is advantageous over that based on traditional PEC in terms of inspection sensitivity and accuracy of corrosion imaging.
39 citations
TL;DR: In this paper, a new measurement approach is presented using eddy current testing techniques, and then, an inversion algorithm is proposed and proved efficient and applicable, of which the maximum experimental relative error is within 10%.
Abstract: To ensure the key structural performance in high-temperature and high-stress environments, thermal barrier coatings (TBCs) are often adopted in engineering. The thickness of these multi-layer conductive coatings is an important quality indicator. In order to measure the thickness of multi-layer conductive coatings, a new measurement approach is presented using eddy current testing techniques, and then, an inversion algorithm is proposed and proved efficient and applicable, of which the maximum experimental relative error is within 10%. Therefore, the new approach can be effectively applied to thickness measurement of multi-layer conductive coatings such as TBCs.
38 citations
TL;DR: In this paper, a comprehensive review of finite element analysis (FEA) applied by researchers to calibrate and improve existing and developing electromagnetic non-destructive testing and evaluation techniques, including but not limited to magnetic flux leakage (MFL), eddy current testing, electromagnetic-acoustic transducers (EMATs).
Abstract: The paper contains an original comprehensive review of finite element analysis (FEA) applied by researchers to calibrate and improve existing and developing electromagnetic non-destructive testing and evaluation techniques, including but not limited to magnetic flux leakage (MFL), eddy current testing, electromagnetic-acoustic transducers (EMATs). Premium is put on the detection and modelling of magnetic field, as the vast majority of ENDT involves magnetic induction, either as a primary variable MFL or a complementary phenomenon (EC, EMATs). FEA is shown as a fit-for-purpose tool to design, understand and optimise ENDT systems, or a Reference for other modelling algorithms. The review intentionally omits the fundamentals of FEA and detailed principles of NDT. Strain-stress FEA applications in NDT, especially in ultrasonography and hole-drilling methodology, deserve as well a separate study.
34 citations
TL;DR: In this paper, the maximum eddy current testing that can detect subsurface defect in the carbon steel S45C block was designed, fabricated and investigated, and the weld probe with diameter 16mm was used to perform the inspection.
Abstract: Background/Objectives: Eddy current testing is one of the most widely Non Destructive Evaluation (NDE) methods which utilized in the industry especially in oil and gas, aircraft, nuclear and coating industries. Experimental studies of eddy current testing have emerged as an important approach alongside numerical. This paper is to design, fabricate and investigate the maximum eddy current testing that can detect subsurface defect in the carbon steel S45C block. Methods/Statistical Analysis: The material of the artificial defect block is carbon steel (S45C) with dimension of 180mm (length) × 25mm (width) × 60mm (height). There are eight artificial defects which located 20mm parallel to the length of the block with 0.5mm diameter. The distance defect is located in between 0.5mm to 4.00mm from the surface of the artificial defect block. Weld probe with diameter size of 16mm and 9mm are used to perform the inspection. Findings: Experiments showed that the weld probe with diameter 16mm able to detect subsurface defect up to 4.0mm and 2.0mm for 9mm diameter weld probe. The optimum of eddy current testing frequency for carbon steel S45C is depending on the defect distance from the material surface. Applications/Improvements: The results prove that the maximum depth of the subsurface can be measured by using eddy current testing method, which is depending on the frequency of the exciting coil weld probe.
33 citations
TL;DR: In this paper, a closed-form expressions of PMEC responses to subsurface corrosion are formulated via the Extended Truncated Region Eigenfunction Expansion (ETREE) modelling.
Abstract: Due to corrosive and hostile environment, in-service conductive structures are prone to subsurface corrosion which has posed a severe threat to structural integrity and safety. Although Pulsed eddy current testing (PEC) has been found advantageous over other Electromagnetic Non-destructive Evaluation (ENDE) techniques particularly in detection and characterisation of subsurface defects in conductive structures, it is subject to technical drawbacks. In light of this, in this paper, Pulse-modulation eddy current technique (PMEC) is proposed in an effort to enhance the inspection sensitivity to subsurface corrosion and quality of corrosion imaging. Closed-form expressions of PMEC responses to subsurface corrosion are formulated via the Extended Truncated Region Eigenfunction Expansion (ETREE) modelling. A series of simulations are subsequently conducted to analyse the characteristics of PMEC signals and inspection sensitivity. Following this, experiments of PMEC for evaluation and imaging of subsurface corrosion are carried out. Through theoretical and experimental investigation, it has been found that PMEC is advantageous over PEC in terms of evaluation sensitivity and quality of corrosion imaging.
33 citations
22 Sep 2016
TL;DR: The results show the usefulness of the proposed approach to be used as an aided tool for ECT data analysis, which allows both an easier and shorten data interpretation by the qualified inspectors, and an increase in the diagnosis quality.
Abstract: In the framework of Eddy Current Testing (ECT), this work presents an automated non-destructive testing method based on Eddy Currents which uses few geometric features of low definition Lissajous figures. A features vector representing the shape of the ECT magnetic field response represented in the complex plane is used as signature to recognize specific defects of aerospace structures. In order to evaluate the proposed method, the accuracy, specificity, sensitivity, precision, F-Measure, AUC, and Matthews correlation coefficient are used to rate the following classifiers: J48, multi-layer neural network and Naive Bayes. The used data set is carried out by lab experiments performed on an aircraft test-piece with several well-known defects. The results show the usefulness of the proposed approach to be used as an aided tool for ECT data analysis. It allows both an easier and shorten data interpretation by the qualified inspectors, and an increase in the diagnosis quality.
32 citations
TL;DR: In this paper, an overview of previous studies on the eddy current testing of Carbon Fiber Reinforced Plastic (CFRP) composites is presented, and the available numerical simulation methods for the electromagnetic modeling of CFRP materials and the calculation of eddy currents and ECT signals.
Abstract: This paper presents the overview of previous studies on the eddy current testing of Carbon Fiber Reinforced Plastic (CFRP) composites. CFRP is composed of many unidirectional carbon fiber/epoxy plies stacked together, thus it has laminated structure and inhomogeneous nature. Eddy Current Testing (ECT) is an efficient and non-contact Nondestructive Testing (NDT) technique for conductive materials. The electrical conductivity of carbon fibers can be utilized by ECT system for fiber texture mapping and detection of defects that can cause the conductivity change. Recently a lot of attention has been paid to the electromagnetic properties characterization of CFRP material, fiber texture and defect detection, as well as the ECT technique enhancement. In this paper we will give the detailed information and results of these research works. In addition this paper also summarizes the available numerical simulation methods for the electromagnetic modeling of CFRP materials, and the calculation of eddy currents and ECT signals.
TL;DR: In this paper, the influence of metallic shields on circular PEC sensor for defect detectability in ferromagnetic metals has been investigated through finite element models (FEM) and experimental studies by comparing iron and aluminum shields with no-shield.
Abstract: Pulsed eddy current (PEC) with transient analysis is a significant advance over conventional eddy current testing using impedance analysis at a particular frequency. The fabrication and optimization of PEC sensor are important issues in PEC applications in nondestructive testing (NDT) field especially for ferromagnetic materials. In this work, the influence of metallic shields on circular PEC sensor for defect detectability in ferromagnetic metals has been investigated through finite element models (FEM) and experimental studies by comparing iron and aluminum shields with no-shield. Both simulations and experiments indicate that PEC probe with an aluminium shield can effectively enhance the amplitude of PEC response in both surface and subsurface defect detection. However, the sensitivity is decreased. In contrast, iron shield has better shielded performance and can effectively improve the sensitivity of both surface and subsurface defects detection in ferromagnetic materials.
TL;DR: In this article, an inversion problem solution was proposed to obtain the geometrical profile of defects in a 2D surface view using an eddy current method with sinusoidal excitation.
Abstract: This paper presents an inversion problem solution to obtain the geometrical profile of defects in a 2D surface view using an eddy current method with sinusoidal excitation. The inversion model deals with the perturbation of the eddy currents when a spatially uniform excitation magnetic field distribution is imposed in the vicinity of a metal surface. An adequate experimental setup was used to measure the magnetic field around a crack region. A planar excitation coil was used to generate the uniform magnetic field distribution around the points under measurement, and a giant magneto-resistance (GMR) was used as a sensing element. Tikhonov regularization was applied to the inversion problem algorithm. Five different geometric defects machined in an aluminum plate were tested experimentally using the inversion algorithm. Finite element simulations are provided to validate the 2D eddy current density images obtained by the regularized inversion process.
TL;DR: In this article, a high-temperature superconducting (HTS) coil was used to measure the thickness of an iron plate and the effect of the liftoff between the plate and HTS coil on the changes in the inductance L and the resistance R of the coil was studied.
Abstract: We applied low-frequency eddy current testing (ECT) using a high-temperature superconducting (HTS) coil in order to measure the thickness of an iron plate. Using this method, we measured changes in coil impedance when the iron plate was placed below the coil. Although low-frequency measurements were necessary to avoid the skin effect, changes in coil impedance became very small at low frequencies. For this reason, an HTS coil was used in order to sensitively measure these small changes. First, changes in the inductance L and the resistance R of the coil were measured when the iron plate was positioned 18 mm below the HTS coil, and the thickness of the plate was changed in increments from 6 to 22 mm. The results show that we were able to estimate the thickness of the plate up to 22 mm based on the changes in R when an excitation frequency of 4 Hz was used. Next, the effect of the liftoff between the iron plate and the HTS coil on the changes in Land R was studied while the liftoff was changed from 18 to 28 mm. The results show that the liftoff could be estimated from the changes in L. We were therefore able to determine the liftoff and the thickness of the iron plate by measuring changes in L and R, respectively. Results obtained from numerical simulation using the finite element method were in agreement with the experimental results.
TL;DR: In this paper, a non-intrusive generalized polynomial chaos expansion is used in order to quantify the impact of multiple unknown input parameters such as magnetic remanence and lift-off distance.
Abstract: The paper addresses the analysis of uncertainties in the framework of the nondestructive evaluation technique Lorentz force eddy current testing. A non-intrusive generalized polynomial chaos expansion is used in order to quantify the impact of multiple unknown input parameters. In this context, the statistics of the velocity and the conductivity of the specimen as well as the magnetic remanence and the lift-off distance of the permanent magnet are determined experimentally and modeled as $\beta $ -distributed and uniform distributed random variables. The results are compared with Monte Carlo simulations and showed errors <0.2%. Furthermore, the numerically predicted force profiles are validated with experiments. A sensitivity analysis by means of the Sobol decomposition revealed that the magnetic remanence and the lift-off distance contribute to more than 90% of the total variance of the resulting Lorentz force profile and should be considered first to improve reproducibility.
Dissertation•
01 Jan 2016
TL;DR: In this article, the authors present an Intelligent Mechatronic Systems Group Doctor of Philosophy (DIPS) at the University of Engineering and IT (UEIT) Intelligent Intelligent MEchatronic System Group (IMSG).
Abstract: Faculty of Engineering and IT Intelligent Mechatronic Systems Group Doctor of Philosophy
08 Mar 2016
TL;DR: In this article, the authors presented 2D images of the eddy current distribution in an aluminium plate by inverting the corresponding magnetic field, and the magnetic field maps were inverted using Tikhonov regularization.
Abstract: This paper presents 2D images of the eddy current distribution in an aluminium plate by inverting the corresponding magnetic field. Three linear defects with different lengths (5 mm, 8 mm, 12 mm) were machined in a 4 mm thick aluminium plate. The magnetic field maps were obtained experimentally using an eddy current measurement setup to scan the defect regions. The probe included in the system contains a planar coil to excite a sinusoidal current with spatially uniform current distribution, and a GMR sensor to measure one magnetic field component. The magnetic field maps were inverted using Tikhonov regularization. A proper choice of the regularization parameter value is essential for the success of the inversion method. In the present paper the determination of the regularization parameter was automated by careful analysis of the energy evolution of the current density data as a function of the regularization parameter. The validation of the resulting regularization parameters was obtained comparing this method with the well-known L-curve. The advantages and disadvantages of the two methods are discussed. Finally, the inversion method with parameter selection was tested with an experimental magnetic field map containing information about an L-shaped defect with length equal to 10 mm to estimate the performance of the proposed method in non-linear cracks.
TL;DR: In this article, the authors used the Coupling method of magnetic memory and eddy current (CMMEC) testing for crankshafts to verify the validity of the coupling method.
Abstract: To verify the validity of the Coupling method of magnetic memory and eddy current (CMMEC) testing for crankshafts, we use this technique to test a 12-cylinder V-design diesel crankshaft. First, the stress distribution in the crankshaft was obtained under 12 working conditions using a Finite element (FE) model that complied with the commercial FE code ABAQUS. Second, Magnetic memory testing (MMT) and Eddy current testing (ECT) were adopted to detect the regions of stress concentration in the crankshaft and the specific location of cracks based on simulation results. Lastly, magnetic particle testing was conducted to detect and display the corresponding crack to verify the CMMEC testing results. The MMT and ECT results can provide basis and guidance for the remanufacture and life evaluation of retired crankshafts.
TL;DR: In this paper, the authors demonstrate that 3D printing technology offers a simple, easy, and cost-effective method to fabricate artificial flaws simulating real cracks from the viewpoint of eddy current testing.
TL;DR: There is no need to subtract the average value of the sensing coils, and it is sensitive to ringed defects, and a relatively highly accurate image of local defects is obtained by these sensing coils.
Abstract: In the non-destructive testing of ferromagnetic pipes based on remote field eddy currents, an array of sensing coils is often used to detect local defects. While testing, the image that is obtained by sensing coils exhibits a ghost-image, which originates from both the transmitter and sensing coils passing over the same defects in pipes. Ghost-images are caused by transmitters and lead to undesirable assessments of defects. In order to remove ghost-images, two pickup coils are coaxially set to each other in remote field. Due to the time delay between differential signals tested by the two pickup coils, a Wiener deconvolution filter is used to identify the artificial peaks that lead to ghost-images. Because the sensing coils and two pickup coils all receive the same signal from one transmitter, they all contain the same artificial peaks. By subtracting the artificial peak values obtained by the two pickup coils from the imaging data, the ghost-image caused by the transmitter is eliminated. Finally, a relatively highly accurate image of local defects is obtained by these sensing coils. With proposed method, there is no need to subtract the average value of the sensing coils, and it is sensitive to ringed defects.
TL;DR: In this paper, a new inducer of pulsed eddy current thermography (PECT) is presented, which can help avoid the problem of blocking the infrared (IR) camera's view of the test specimen.
Abstract: In this paper, a new inducer of pulsed eddy current thermography (PECT) is presented. The use of the inducer can help avoid the problem of blocking the infrared (IR) camera’s view in eddy current thermography technique. The inducer can also provide even heating of the test specimen. This paper is concerned with the temperature distribution law around the crack on a specimen when utilizing the new inducer. Firstly, relative mathematical models are provided. In the following section, eddy current distribution and temperature distribution around the crack are studied using the numerical simulation method. The best separation distance between the inducer and the specimen is also determined. Then, results of temperature distribution around the crack stimulated by the inducer are gained by experiments. Effect of current value on temperature rise is studied as well in the experiments. Based on temperature data, temperature features of the crack are discussed.
21 Oct 2016
TL;DR: In this paper, the authors presented the possibility of applying eddy current thermography method for detecting defects in ballistic covers made of carbon fiber reinforced composites used in the construction of military vehicles.
Abstract: Eddy current thermography is a new NDT-technique for the detection of cracks in electro conductive materials. It combines the well-established inspection techniques of eddy current testing and thermography. The technique uses induced eddy currents to heat the sample being tested and defect detection is based on the changes of induced eddy currents flows revealed by thermal visualization captured by an infrared camera. The advantage of this method is to use the high performance of eddy current testing that eliminates the known problem of the edge effect. Especially for components of complex geometry this is an important factor which may overcome the increased expense for inspection set-up. The paper presents the possibility of applying eddy current thermography method for detecting defects in ballistic covers made of carbon fiber reinforced composites used in the construction of military vehicles.
23 May 2016
TL;DR: This paper presents the characterization of cracks in a metallic material using an eddy current testing technique called alternating current field measurement (ACFM), which is limited in the ability to detect cracks when induced currents flow parallel to it.
Abstract: This paper presents the characterization of cracks in a metallic material using an eddy current testing technique called alternating current field measurement (ACFM). This technique has already shown good results in the field of defect detection because, the current is forced to flow in a uniform direction, making it more predictable and easy to interpret the behavior of the induced current when a crack is present in the metal. However, this technique is limited in the ability to detect cracks when induced currents flow parallel to it. In this paper, a planar probe was built to remove this difficulty. The probe includes two planar coils that induce current in the conductor in different directions and two giant magnetoresistive (GMR) sensors positioned perpendicularly to each other to measure the two perpendicular components of the magnetic field. The Inverse problem technique was applied to get the current density maps from the magnetic field maps. 2D eddy current density images were obtained to visualize the crack geometry.
09 May 2016
TL;DR: 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 as mentioned in this paper.
Abstract: Eddy current testing is well established for non-destructive testing of electrical conductive materials. 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. 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.
10 Apr 2016
TL;DR: In this paper, an innovative inversion strategy is presented to address the non-invasive inspection of large conductive structures by exploiting eddy current testing (ECT) measurements, which is formulated within the Learning-by-Examples (LBE) framework and is solved by means of an efficient strategy that combines Partial Least Squares (PLS) feature extraction with an adaptive sampling strategy in order to generate optimal training databases during the off-line phase, while exploits Support Vector Regression (SVR) during the on-online phase for achieving robust and accurate estimations with almost real
Abstract: An innovative inversion strategy is presented to address the non-invasive inspection of large conductive structures by exploiting eddy current testing (ECT) measurements. The arising inverse problem is formulated within the Learning-by-Examples (LBE) framework and is solved by means of an efficient strategy that combines Partial Least Squares (PLS) feature extraction with an adaptive sampling strategy in order to generate optimal training databases during the off-line phase, while exploits Support Vector Regression (SVR) during the on-line phase for achieving robust and accurate estimations with almost real-time prediction performances.
TL;DR: A new method to quantitatively evaluate the eddyCurrent distribution induced by different exciting coils of an eddy current probe and a method to calculate angular spectral density and Shannon information entropy is proposed.
Abstract: Here, a new method is proposed to quantitatively evaluate the eddy current distribution induced by different exciting coils of an eddy current probe. Probability of energy allocation of a vector field is modeled via conservation of energy and imitating the wave function in quantum mechanics. The idea of quantization and the principle of circuit sampling is utilized to discretize the space of the vector field. Then, a method to calculate angular spectral density and Shannon information entropy is proposed. Eddy current induced by three different exciting coils is evaluated with this method, and the specific nature of eddy current testing is discussed.