Non-Destructive Techniques Based on Eddy Current Testing
TL;DR: An overview of the fundamentals and main variables of eddy current testing is included, and the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems are described.
Abstract: Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.
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TL;DR: An experimental study of the effect of temperature on the electrical impedance of the piezoelectric sensors used in the EMI technique showed that the temperature effects were strongly frequency-dependent, which may motivate future research in the SHM field.
Abstract: The electromechanical impedance (EMI) technique is considered to be one of the most promising methods for developing structural health monitoring (SHM) systems. This technique is simple to implement and uses small and inexpensive piezoelectric sensors. However, practical problems have hindered its application to real-world structures, and temperature effects have been cited in the literature as critical problems. In this paper, we present an experimental study of the effect of temperature on the electrical impedance of the piezoelectric sensors used in the EMI technique. We used 5H PZT (lead zirconate titanate) ceramic sensors, which are commonly used in the EMI technique. The experimental results showed that the temperature effects were strongly frequency-dependent, which may motivate future research in the SHM field.
200 citations
Cites methods from "Non-Destructive Techniques Based on..."
...There are several nondestructive testing (NDT) methods [2] that are used to detect structural damage, such as Lamb waves [3,4], acoustic emission testing [5,6], comparative vacuum monitoring [7], and eddy current testing [8]....
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TL;DR: In this paper, a chipless RFID sensor tag integrating four tip-loaded dipole resonators as a 4-bit ID encoder and a circular microstrip patch antenna (CMPA) resonator as a crack sensor is proposed.
Abstract: Chipped radio-frequency identification (RFID) sensor systems have been studied for structural health monitoring (SHM) applications. However, the use of chip in sensor tags and its standardized narrowband operation contribute shortcomings in cost, durability, and detection capability. This paper presents a novel use of the frequency signature-based chipless RFID for metal crack detection and characterization operating in ultra-wideband frequency. The vision is to implement a low-cost and high-temperature-resistant passive wireless sensor able to monitor the crack on a metallic structure with multiparameter detection. We propose a chipless RFID sensor tag integrating four tip-loaded dipole resonators as a 4-bit ID encoder and a circular microstrip patch antenna (CMPA) resonator as a crack sensor. The radar cross section spectrum of the chipless RFID sensor tag generates four resonant frequencies from the dipole resonators and a resonant frequency from the CMPA resonator. Simulation and experimental results show that the resonant frequency shift of the CMPA is a useful feature to indicate the crack orientation and the crack width on a metallic structure. The direction of the resonant frequency shift represents the orientation of the crack, while the magnitude of the resonant frequency shift is proportional to the width of the crack. Furthermore, the experimentation with a natural fatigue crack sample proves that the proposed sensor tag is capable of detecting submillimeter cracks.
152 citations
Cites methods from "Non-Destructive Techniques Based on..."
...ultrasonic testing [5], eddy current testing [6], thermography testing [7], and microwave waveguide testing [8], which have...
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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
06 Sep 2017
TL;DR: In this article, the authors provide a comprehensive overview of the issues that need to be addressed by any large-area characterisation method for electrical key performance indicators, with emphasis on electrical uniformity and on how this can be used to provide a more accurate analysis of the graphene film.
Abstract: The significant progress in terms of fabricating large-area graphene films for transparent electrodes, barriers, electronics, telecommunication and other applications has not yet been accompanied by efficient methods for characterizing the electrical properties of large-area graphene. While in the early prototyping as well as research and development phases, electrical test devices created by conventional lithography have provided adequate insights, this approach is becoming increasingly problematic due to complications such as irreversible damage to the original graphene film, contamination, and a high measurement effort per device. In this topical review, we provide a comprehensive overview of the issues that need to be addressed by any large-area characterisation method for electrical key performance indicators, with emphasis on electrical uniformity and on how this can be used to provide a more accurate analysis of the graphene film. We review and compare three different, but complementary approaches that rely either on fixed contacts (dry laser lithography), movable contacts (micro four point probes) and non-contact (terahertz timedomain spectroscopy) between the probe and the graphene film, all of which have been optimized for maximal throughput and accuracy, and minimal damage to the graphene film. Of these three, the main emphasis is on THz time-domain spectroscopy, which is non-destructive, highly accurate and allows both conductivity, carrier density and carrier mobility to be mapped across arbitrarily large areas at rates that by far exceed any other known method. We also detail how the THz conductivity spectra give insights on the scattering mechanisms, and through that, the microstructure of graphene films subject to different growth and transfer processes. The perspectives for upscaling to realistic production environments are discussed. TOPICAL REVIEW 2017 Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. RECEIVED
111 citations
Additional excerpts
...Similar to the micro four-point probe, the method allows information on the large-scale homogeneity of the sample to be extracted as well, since disruptions such as cracks, force the eddy currents to pass around the obstacle, which can be detected as a shift of impedance [113]....
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TL;DR: In this paper, the state-of-the-art NDT methods for damage detection and characterization in composite laminates for use in the aircraft primary and secondary structures are reviewed.
106 citations
References
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TL;DR: In this paper, the authors introduced the application of principal component analysis (PCA) in extracting information from PEC responses, which has performed better than the conventional technique in the classification of defects.
Abstract: Pulsed Eddy current (PEC) is a new emerging NDT technique for sub-surface defect detection. The technique mainly uses the response peak value and arrival to detect and quantify the defects. This could suffer from noise and be not sufficient to extract more information about the defects, e.g. depth information of defects. This paper introduces the application of principal component analysis in extracting information from PEC responses. A comparative test carried out shows that the introduced technique has performed better than the conventional technique in the classification of defects.
290 citations
"Non-Destructive Techniques Based on..." refers methods in this paper
...The performance of defect classification using the pulsed technique is better than the conventional method [47]....
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TL;DR: In this article, a three axis magneto-resistive magnetic field sensor is used to measure the residual magnetic fields parallel to the applied stress and the material surface (Bx) and perpendicular to Bx, generated by the magnetomechanical effect without the application of an external field, using steel samples exposed to stresses.
Abstract: The evaluation of both applied and residual stresses in engineering structures to provide early indications of stress status and eventual failure is a fast growing area in non-destructive testing. Much work has been done in recent years in the development of magnetic stress measurement techniques for ferromagnetic materials using applied magnetic fields to monitor changes in the magnetic properties of materials, such as variations in the hysteresis curve or Barkhausen emission. But the area of passive field measurement is relatively unexplored. When magnetic metals are strained, they irreversibly transformed from a non-magnetic state to a magnetic state, this is referred to as metal magnetic memory (MMM) or the residual magnetic field (RMF). This paper investigates the phenomena under different circumstances and applies the residual magnetic field technique to stress measurement. A three axis magneto-resistive magnetic field sensor is used to measure the residual magnetic fields parallel to the applied stress and the material surface (Bx) and perpendicular to the material surface (Bz), generated by the magneto-mechanical effect without the application of an external field, using steel samples exposed to stresses. The test results show that without using an applied field, the stresses in a sample can be measured using magnetic field sensing, with Bx showing particularly good correlation. The work concludes that the novel passive field technique including analysis of the magnetic field pattern and magnetic field variation rate, would prove advantageous in certain circumstances, for example in-service inspection of structures with complex geometries. Further research directions are also highlighted.
171 citations
TL;DR: In this paper, the development of non-destructive techniques (NDT) techniques for the in-service inspection of railroad wheels and gauge corners was the main activity of the NDT division VIII. 4 at BAM over the last 2 years.
Abstract: The development of non-destructive techniques (NDT) techniques for the in-service inspection of railroad wheels and gauge corners was the main activity of the NDT division VIII. 4 at BAM over the last 2 years. For such different components, two different inspection techniques were fundamentally chosen in order to fulfil the end-user requirements. Firstly the inspection of the wheels—rim and disk—should be carried out without dismantling the wheels and using ultrasonic techniques. On the other hand, the inspection of the railroad track surface at a train speed of about 70 km/h should be guaranteed using eddy current techniques. The above-mentioned tasks were a challenge for the lab staff. The accessibility for the wheel inspection was limited due to several impassable barriers such as sand tubes, etc. Eddy current application focused mainly on the detection of head check defects occurring at the gauge corner of the rail. Investigations carried out also showed, that other types of surface defects (e.g. Belgrospis, wheel burns, short-pitch corrugations, etc.) could easily be detected. Some aspects of the inspection system as well as an overview of test results are presented in the current contribution.
146 citations
"Non-Destructive Techniques Based on..." refers background in this paper
...have proposed railroad track surface testing at train speeds of 70 km/h [14]....
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...Eddy current on the test piece (adapted from [14])....
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TL;DR: In this paper, three different probes, including a differential hall probe, a differential coil probe, and a two-stage differential coils probe, are designed to detect the defects between third layer and fourth layer in riveted structures.
Abstract: The Pulsed Eddy Current (PEC) technique is an effective method of quantifying defects in multi-layer structures. It is difficult to detect defects in riveted structures of aging aircraft. Based on theoretical analysis of PEC technique, three different probes, including a differential hall probe, a differential coil probe, and a two-stage differential coil probe are designed to detect this kind of defects. The averaging method and wavelet analysis method are used to de-noise the hall response signals. By selecting peak amplitude and zero-crossing time of response signal in time domain as key features, defects in riveted structures can be detected effectively. The experimental results indicated that the differential coil probe acted as effectively as the differential hall probe. The defects between third layer and fourth layer in riveted structures can be detected by utilizing the two-stage differential coil probe. The PEC technique has a promising application foreground in the field of aeronautical nondestructive testing.
146 citations
"Non-Destructive Techniques Based on..." refers background or methods in this paper
...They used an averaging method and wavelet de-noise method to process the Hall responses [50]....
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...tested the use of a differential hall probe to detect defects in the riveted structures of aircrafts [50]....
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...Typical features such as peak amplitude and zero-crossing time of pulses are employed to detect and characterize defects [50]....
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01 Jan 2002
TL;DR: In this article, two fundamentally different inspection techniques were chosen in order to satisfy the end-user requirements: rim and disk inspection without dismantling the wheels and using ultrasonic techniques, and inspection of the railway track surface at a train speed of about 70 km/h using eddy current techniques.
Abstract: The development of NDT techniques for the in-service inspection of railway wheels and gauge corners were the main activities of the NDT division VIII.4 at BAM over the last two years. For such different components, two fundamentally different inspection techniques were chosen in order to fulfil the end-user requirements. Firstly the inspection of the wheels - rim and disk - should be carried out without dismantling the wheels and using ultrasonic techniques. On the other hand the inspection of the railway track surface at a train speed of about 70 km/h should be guaranteed using eddy current techniques. The above mentioned tasks were a challenge for the personnel involved. The accessibility for the wheel inspection was limited due to several impassable barriers such as sand tubes etc. Eddy current application focused mainly on the detection of head check defects occurring at the gauge corner of the rail. Investigations carried out also showed that other types of surface defects (e.g. Belgrospis, wheel burns, short-pitch corrugations etc.) can easily be detected. In the present contribution some aspects of the inspection system as well as an overview of test results are presented. For the covering abstract see ITRD E122683.
135 citations