Ebook: Electromagnetic Non-Destructive Evaluation (XXIII)

The 24th International Workshop on Electromagnetic Nondestructive Evaluation (ENDE2019) was held on September 11 to 14, 2019 at the Longemont Hotels in Chengdu, China. The workshop was organized by the University of Electronic Science and Technology of China (UESTC) and co-organized by Southwest Jiaotong University and Sichuan University. A total of 146 registered participants from 15 countries worldwide in the field of nondestructive evaluation attended the workshop.

ENDE 2019 aims to bring together engineers and scientists active in the research, development, and industrial application of Electromagnetic Nondestructive Evaluation (ENDE). It provided participants with a fantastic opportunity to exchange ideas and update on the latest developments. This year’s technical sessions, poster competitions and special ENDE events focused on theoretical and applied research on ENDE methods. A total of 127 contributed technical presentations were organized into two poster sessions plus eight oral sessions covering topics on (i) QNDE and AI in ENDE and systems, (ii) ENDE sensors and numerical modelling, (iii) Analytical and numerical modelling, (iv) ENDE application, (v) ENDE application for high-speed railway, (vi) Material characterization, (vii) Inverse problems and signal processing. Through a range of technical and social activities, ENDE 2019 offered all the participants a unique opportunity to interact with the world’s leading experts in electromagnetic NDE from academia, industry, and government.

Prof. Guiyun Tian, the general chair of ENDE 2019, welcomed all the attendees to the workshop and provided introductory remarks to open the workshop. The technical program commenced with two keynote speeches: (i) “Electromagnetic NDE Techniques for Inspecting Composite Materials and Additively Manufactured Components” by Prof. Satish Udpa, IEEE fellow, Michigan State University, United States; (ii) “R&D of NDT Technologies for Nuclear Power Plant and Applications” by Prof. Yong Nie, Deputy Chief Engineer, China Nuclear Power Operation Technology Corporation Ltd., CNNC, China. Three distinguished speakers from eddy current nondestructive evaluation, healthcare, and flexible tactile sensors were invited to discuss challenges confronting them and the ways in which NDE can assist in addressing these issues. An invited talk entitled “Adaptive Cross Approximations for Eddy Current Nondestructive Evaluations” was given by Prof. Jiming Song from the Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa, USA, introducing the formulation of eddy current problem using the Boundary Element Method (BEM). Another invited talk entitled “Translating Engineering to Healthcare” was given by Dr. James Avery from the Department of Surgery and Cancer, St Mary’s Hospital Imperial College, UK, discussing the electromagnetic sensing and imaging from a biomedical perspective, from tracking surgical tools, medical robotics, implantable sensors, neuroscience, tomographic imaging and spectroscopy; the third invited talk entitled “Flexible tactile sensors based on patterned nanostructures of graphene and 2D materials” was given by Prof. Pingan Hu from the School of Materials Science and Engineering Harbin Institute of Technology (HIT), Harbin, China, presenting the development of highly sensitive and conformal pressures sensors for any curved surface using two dimensional (2D) nanomaterials.

The 24th book, following ENDE 2019, is proposed herein, as an Open Access publication on the IOS Press Ebooks platform, including 38 peer-reviewed extended contributions from the original 45 submissions. This suite of book covers recent studies concerning the progress and applications of Electromagnetic (EM) fields to nondestructively inspect, test, evaluate, and characterize materials and structures. More specific paper topics cover from micro-structural levels, such as correlating the magnetic properties of a material with its grain structure, to macroscopic ones, such as techniques for EM NDT&E and applications. Recent developments of emerging materials such as advanced EM sensors, multi-physics NDT&E, intelligent data management and maintaining the integrity of structures with material characterization, natural defects are included as well.

To conclude, the organizers would like to thank all members of the International Standing Committee, who provided much guidance and support through their successful ENDE experiences in past years. We also gratefully acknowledge the support of all reviewers of extended papers who have played a key role in the making of these proceedings, and Dr Yan Yan and Mr Kun Zeng for the help of editing this book. Lastly, we acknowledge the hard work of student volunteers, whose dedication and interactions with all ENDE participants ensured the smooth and successful operation of the ENDE2019 Workshop and the book preparation.

University of Electronic Science and Technology of China

Guiyun Tian

General Chair, ENDE 2019

Bin Gao

Co-Editor

The induced ferrite and other high magnetic microstructures content changes are studied when 304 austenitic stainless steel stripe specimens are tested under different uniaxial tension deformation, namely its deformation less than 50%. Furtherly, the correlation is plotted between the resulting magnetic permeability or coercivity caused by these microstructures and deformation. Meanwhile, the optimal eddy current excitation frequency under different deformation was obtained, which was consistent with 3-D finite element analysis (FEA). Besides, other various factors affecting the quality of eddy current testing (ECT), such as temperature and conductivity, are also considered comprehensively during the tensile test. The results of the experiment and simulation calculation show that when the deformation is within 50% that necking deformation has occurred, the magnetic permeability of specimens increases with deformation, and gradually begin to have the magnetic properties of weak ferromagnetic materials, which also changes the optimal excitation frequency, which varies from 60 kHz to 110 kHz. Because of the electromagnetic response noise increase, the impedance plane diagrams of defects distort simultaneously, which leads to the quantitative evaluation error of defects.

The lightning strike protection layer, which is a mesh of metal stripes, is adhered to composite materials to dissipate the huge current induced during lightning strike. This paper presents an eddy current imaging method to inspect defects in the lightning strike protection layer. A tuning method was applied to tune the resonant frequency of excitation and sensing coils and enhance the testing results. Two parameters, namely the amplitude of induced voltage in the sensing coil and the amplitude of the voltage across a sampling resistor in the excitation circuit, were used to image the defects. The results show that the image formed by sensing coil voltage is less noisy and more accurate.

This paper proposes to evaluate the local wall thinning of carbon steel pipe using an eddy current method. Firstly, the feature signals are determined by correlation analysis of the signals and the wall thinning sizes. Subsequently, the models for estimating the residual wall thickness rt is constructed using Gaussian process regression (GPR). Finally, the applicability of the models to the evaluation of local wall thinning is verified by simulation and experiment.

The lay length is one of the important parameters for the wire rope and its detection can indirectly characterize its stress and surface damage state. The eddy current testing (ECT) method is advantageous because of its easy operation, single-side detection, low requirement of surface preparation, applicability in harsh environment, and other properties. Hence the lay length of the wire ropes is measured by ECT in this paper. The eddy current (EC) response to the wire rope is simulated. The EC on the surface of the strand below the pancake coil forms a vortex, and the distribution of the EC on the curved surfaces on both sides of the strand is symmetrical. The spacing between the adjacent peaks or troughs of the scanning signal is the distance between the adjacent strands, and the number of peaks or troughs of the scanning signal in a range of the lay length is related to the number of strands of the wire rope. Finally, the experimental validation is performed. The relative error of the lay length of the wire rope assessed by the EC method is less than 0.28%.

The Transmitter-Receiver Probe (TR probe), which has improved signal-to-noise ratio, deep penetration depth, and directional measurement is used in pulsed eddy current testing (PECT). Whereas, the lift-off effect on the TR probe is one of the main obstacles. The purpose of this paper is to analyze the lift-off effects on the TR probe and presents a feature for lift-off estimation. Firstly, an analytical model of a TR probe is given based on previous studies. Secondly, on the basics of the analytical model, the spectrum of the PECT signal is studied, and the lift-off effects on the TR probe are analyzed. Then, the lift-off effects under different coil distances are studied and a D Intersect Point (DIP) is proposed for the lift-off estimation. Results show that the TR probe can be used to reduce the lift-off effect for the non-ferromagnetic materials and the ferromagnetic materials. And both the DIP time and amplitude can be used for lift-off estimation. However, the DIP time is better, as its evolution curve with lift-off is a straight line with the same slope. The study is believed to be helpful for the TR probe design, the lift-off measurement, and the thickness assessment and defect quantification.

Structural health monitoring of steel structures is crucial for inspection of corrosion and cracking in structural members, compromising their safety and serviceability. In the present study, the prospective of evaluation of change in stress state of structural member due to corrosion and cracking through eddy current based stress measurement is investigated. For this, three-dimensional numerical simulations are carried out in the FE software COMSOL Multiphysics 5.2a for a steel plate subjected to change in relative permeability, representative of change in stress state, whereby the eddy current indices are characterized, including the effects of additional influential parameters namely, lift-off, excitation frequency, and probe size. Phase Diagram is then proposed as a concise method to evaluate the variation of relative permeability and lift-off concurrently in a single graph for an excitation frequency and probe size. It further facilitates the selection of suitable excitation frequency and probe size to conduct the eddy current based stress measurement.

Defective adhesive bonds pose significant threats towards structural integrity due to reduced joint strength. While the nature of the adhesion of two solids remains poorly understood since adhesion phenomenon is relevant to so many scientific and technological areas. A concept that has been gaining our attention from the perspective of nondestructive testing is the properties discontinuity of the adhesion. Discontinued properties depend significantly on the quality of the interface that is formed between adhesive and substrate. In this research, discontinued electrical properties at the interface are considered. The simplified model is free from multidisciplinary knowledge of chemistry, fracture mechanics, mechanics of materials, rheology and other subjects. From a practical standpoint, this emphasizes the need to establish a good relationship between electrical properties of adhesive bonds and corresponding measurements. Capacitive Imaging (CI) is a technique where the dielectric property of an object is determined from external capacitance measurements. Thus, it is potentially promising since adhesive and substrate differ in terms of dielectric property. At the interface between adhesive and substrate, discontinuity of the dielectric properties causes abrupt changes in electric field spatial distribution and thus alters capacitance measurement. By simulating defects in adhesive joints regarding permittivity uncertainties. Further understanding of the cause of degraded adhesion quality can be obtained

Complex geographical conditions and bad weather have caused great difficults to inspect transmission line of power grids. This work aims to develop a micro multi-rotor Unmanned Aerial Vehicle (UAV) system for inspecting power grid. The proposed system integrates with an intelligent robot and mobile communication networks. The high-resolution aerial images of the inspection line can be obtained to improve the operational efficiency and safety. The time period from the front-end signal acquisition to terminal decoding and playback is 1.5s for condition-based maintenance. The system supports TDD-LTE, FDD-LTE, WCDMA, CDMA2000, and other network standards. It also supports the video input signals with the resolution of standard 576i, HD 720p, FHD 1080i, and FHD 1080p. It is compatible with a variety of transmission formats and codes, help to achieve timely, comprehensive and efficient high-resolution aerial image acquisition of patrol lines, and improve operational efficiency and safety, real-time monitoring and condition-based maintenance of power transmission lines.

In order to improve the thickness measurement accuracy of metal plate, a new method based on phase detection thickness is proposed. Two modes of ultrasonic echo are generated by electromagnetic acoustic transducer (EMAT) at the edge of specimen, and super-heterodyne phase-sensitive detection technique is used to collect the phases of the ultrasonic, then the thickness information of the tested specimen is obtained accurately. Firstly, the finite element model of EMAT is built, and the time-domain characteristics of acoustic echo are analyzed. Secondly, the 0^∘ and 90^∘ phase detection on echo signal are detected by the super-heterodyne phase-sensitive detection system. Finally, the relationship between phase information and specimen thickness is analyzed. The results show that the detection method, which based on super-heterodyne phase-sensitive detector of edge mode conversion, can realize the detection of metal plate thickness, and the phase error range is controlled within 0.23%.

Nowadays, there are 160000 kilometers of pipelines in China. How to get more pipeline information in pipeline integrity management is a vitally important research topic. This paper designs a magnetoelectric composite sensor which is suitable for the non-destructive detection of the buried pipeline. according to the defect characteristics. this paper introduces the working principle, structure and characteristics of the composite sensor. Combined with the advantages of the magnetic sensor which is sensitive to the volume defects of the tube wall and the high frequency eddy current sensor which is sensitive to the near-surface defects of the tube wall on the principle of magnetic flux leakage, it realizes the identification and evaluation of the inner and outer wall defects of the tube wall. In this paper, the pipeline in the traction test field is taken as the test object. The test results show that there are 37 defects picked up by the magnetic sensor and 19 defects judged by the eddy current sensor.

We have compared transient potential drop measurements on ferromagnetic steel rods with finite difference simulation assuming that the magnetization varies as a quadratic function of the applied field. Good agreement between simulation and experimental measurement is achieved and the results are discussed in terms of the Rayleigh law of magnetization.

AC induction machines are widely used in electric servo drive, information processing, transportation and other fields. However, the unexpected faults cause the serious threat for the normal operation and operator’s safety. Therefore, timely faults diagnosis is an effective way to ensure the AC induction machines to work in health condition. In AC induction machines, magnetic field is the basis of energy conversion of motor, and the faults have the directly influence on the electromagnetic field distribution. In this paper, 2D numerical model of the AC squirrel-cage asynchronous induction machine is built by using COMSOL Multiphysics according to finite element method; Then, the magnetic flux distribution of AC induction motor with three different faults which commonly occurs in engineering are simulated. Base on the numerical simulation, the influence of the different faults on the magnetic distribution is discussed in detail. The investigation is beneficial to find a nondestructive fault diagnosis approach to the induction machine.

The reliability of micro-damage detection of metal materials plays a crucial role in the safe and reliable operation of large equipment. In recent years, nonlinear ultrasonic nondestructive testing technology has achieved good development in closed cracks detection, but the problem of nonlinear ultrasonic detection of closed cracks is weak response signal and vulnerable to external interference. This paper realizes the modulation of the ultrasonic wave by electromagnetic loading at the closed cracks, which can effectively enrich the frequency components of nonlinear ultrasonic and magnify the amplitude. This lays a foundation for further research on nonlinear ultrasonic detection of closed cracks under electromagnetic loading.

Stress in components will lead to the change of material properties and even failure. Therefore, the assessment for the stress state of components is play an important role in testing industry. As a non-contact and multi-physical field nondestructive testing method, eddy current thermography (ECT) can be applied to detect non-homogeneous electromagnetic characteristics parameter distribution in conductive materials. Internal stress and its distribution in a material will affect the value of electromagnetic characteristic parameters. If induction current applied on conductive material, the Joule’s heat, which generate in the sample will lead to the temperature rise on the surface of the specimen by induction heating process. The temperature distribution on the specimen surface can be recorded by infra camera and stored as IR images or videos. The feature of the temperature distribution and its variation can be used to express the stress state in the specimen. It is concluded that there is an approximate linear relationship between the surface temperature appreciation and the loading force when the excitation source condition remains unchanged.

Magnetic flux leakage (MFL) testing is a widely used electromagnetic nondestructive testing (ENDT) method, which has the ability to detect both surface and sub-surface defects in conductive materials. One of its best features is its ability to mathematically model field leakage from the defect area in a magnetized material. In this paper, we propose an optimized FEM model using geometrical weighted tensor (TBFEM), for the calculation of leakage field in MFL. This model using the Einstein’s convention eliminates the bulky nature of traditional FEM based on its matrix algebra formation allowing for easy implementation and fast calculations. The proposed model achieves this by reducing the set of matrix equations into a single equation using suffixes which can then be solved with regular mathematical operations.

This work describes the validation against experimental data of a Reduced Vector Potential Formulation combined with a boundary condition given by the Dirichlet-to-Neumann operator. One of the classic nondestructive testing problems is investigated: the differential bobbin coil scan inside a tube with a defect. Several defects are simulated, and the results are compared to the experimental data acquired at four frequencies.

Electromagnetic acoustic transducers (EMATs) are widely used in industries due to its non-contact nature. This paper investigates the beam features of unidirectional Rayleigh waves EMATs, especially the effect of the wire length on beam directivity. A wholly analytical model is developed to calculate the Lorentz force distribution and ultrasound displacement distribution. The modelling results indicate that, compared to the coil consists of shorter wires, the coil consists of longer wires results in a narrower bandwidth of main lobe of unidirectional Rayleigh waves, which means the ultrasound are more concentrated. This study can be used for unidirectional Rayleigh waves EMATs design and optimization.

Seven specimens of 45 steel with different residual strains were prepared by homogeneous plastic tensile test. The microstructure of the specimens was observed by scanning electron microscopy and the texture characteristics of the specimens were studied by X-ray diffraction. The results showed that plastic deformation mainly leads to dislocation increment in the microstructure rather than obvious deformed grain morphology, texture and residual stress. Then the dislocation density of each sample was calculated by X-ray diffraction method. The MBN signals of the samples were tested by magnetic Barkhausen noise method and the corresponding RMS (root mean square) values were calculated. The results showed that the dislocation density increases and the RMS value decreases with the increase of plastic deformation magnitude, the phenomenon was explained deeply. By establishing the correlation between dislocation density and RMS value, it was found that there was a good linear relationship between dislocation density and RMS value. According to the formula provided by the fitting curve, the dislocation density can be predicted by measuring the RMS value of any degree of plastic deformation.

Corrosion of steel reinforcing bar (rebar) reduces the strength capacity of concrete, and also causes the crack of concrete due the volume increase of the corrosion products. Detection of corrosion at its early stage is important for the safety evaluation and repairment of the concrete structures. An electromagnetic induction method was developed to evaluate the corrosion of steel rebar. By measuring the electromagnetic response of steel rebar, it was possible to judge the corrosion of steel rebar in concrete. A small compact system, suitable for field experiments was also developed.

Carbon Fiber Reinforced Polymer (CFRP) materials are widely used in aerospace due to their low weigh to strength ratio. Non-destructive Testing (NDT) Techniques becomes a necessity with increasing use of CFRP materials. Induction Thermography is a new NDT technique that can be exploited as a promising fast and global control. However, the detection of typical flaws in carbon composites such as delamination, fibers rupture and impact damages need to be further investigated in order to optimize the technique. Optimization can be done in the test configuration level and by the use an appropriate image technique. In this paper Eddy Current Pulse Compression Thermography (ECPuCT) is used to detect impact damages on CFRP materials. The Principal Component Analysis (PCA) based image processing technique is used to detect and visualize impact damage area from transient thermal images. Flaw detection results using experimental measures will be shown and discussed.