Electromagnetic Nondestructive Evaluation Research Articles

Four-terminal measurement of the distribution of electrical resistance across stress corrosion cracking

This study measures electrical resistance of a stress corrosion crack directly by the four-terminal method to discuss appropriate modeling from the viewpoint of electromagnetic nondestructive evaluation. Two type-316 stainless steel plate specimens containing artificial stress corrosion cracks were prepared, and columnar samples containing penetrating cracks were cut from the plates for the measurements. The results obtained agree with recent reports discussing appropriate numerical modeling of stress corrosion cracking on the basis of finite element simulations. In contrast, this study also reveals that it is not always valid to assume that a stress corrosion crack has uniform conductivity internally.

Preliminary studies on the design principles of capacitive imaging probes for non-destructive evaluation

As a novel electromagnetic non-destructive evaluation (NDE) technique, capacitive imaging (CI) has been successfully used on a various types of materials, including concrete, glass/carbon fibre composite, steel, etc. In this work, studies on the design principles for the CI probes were presented. Firstly, measures for the evaluation of the CI probe performance are presented. The concept of volume of influence is then raised, to evaluate the imaging ability of a given CI probe. Examples of CI probe designs are then provided, namely symmetric and concentric geometries. Design factors, such as separation between electrodes, guard electrodes, and electrode shapes are also discussed and examined experimentally. CI scans were performed on two typical specimens, namely Perspex and aluminium, to evaluation the imaging performance of CI probes with different geometries.

Modeling Some Calibrated Cracks for E-NDE by a Difference Method

Electromagnetic Non Destructive Evaluation (E-NDE) is often conducted by inducing eddy currents in the structure to be examined, if this is conducting. Existence of flaws is detected by difference between the response of defect-free structures and damaged ones. In the present paper, we model such processes in order to predict the feasibility of this evaluation and to facilitate the interpretation of the observation. An original method is to represent a crack by a current source producing a magnetic signal. We have applied it to the case of a defect with a standard shape. The experimental evidences for the validity of this method are given.

Electromagnetic Nondestructive Evaluation: Present and Future

Appearing more than 125 years ago, the electromagnetic nondestructive evaluation has transformed form “art” to an engineering science, which is recognized. This development supposed the elaboration of theories based on Maxwell equations, of adequate transducers and afferent measurement electronics. Together with the development of computer science, the domain has made a spectacular leap. This paper presents a review of theoretical principles, numbering a few methods for solving forward and inverse problems, a review of the principal transducers types, electronics and the possibility of automatic interpretation of control results. Few directions where the domain might develop are sketched, starting from the observation that new types of materials, structures, complex equipments that shall be controlled, permanently appear. The purpose is constituted by obtaining a much higher probability of detecting for the highest possible reliability coefficient for the electromagnetic nondestructive evaluation of materials.

Numerical analysis of an electromagnetic nondestructive evaluation method for rotating machinery

Numerical analysis of an electromagnetic nondestructive evaluation method for rotating machinery

Nondestructive Evaluation of a 6X25 FW Haulage Rope in a Monocable Continuously Moving Passenger Cable Car Installation

Electromagnetic nondestructive evaluation (NDE) of wire rope has been in use for over fifty years. Regular NDE inspections provide a powerful tool in monitoring the rate of degradation of a rope. Wire defects and condition of a haulage rope (construction 6X25 FW) have been studied and presented in this paper.

Some advances in numerical analysis techniques for quantitative electromagnetic nondestructive evaluation

In this paper, some progresses in numerical techniques mainly made in our research group for the forward and inverse simulation of electromagnetic nondestructive evaluation (ENDE) signals are introduced. For the first part, efficient forward analysis schemes for the simulation of eddy current testing (ECT), remote field ECT (RFECT) and magnetic flux leakage testing (MFLT) signals are described respectively, in addition to some numerical examples. Fast and accurate ECT signal simulation is realised by introducing a database type strategy using precalculated unflawed potential field data. To meet the high accuracy requirement of the simulation of RFECT signals, a hybrid scheme using 2D and 3D geometry and a new formula for pickup signal are proposed. To improve the efficiency of MFLT signal simulation, a fast scheme is developed based on a FEM–BEM hybrid code of polarisation method. In addition, a phenomenological method is also described in the first part, which is developed for the qualitative estimation of eddy current distribution and pickup signals. The second part of this review paper is on the reconstruction of defect from the detected ENDE signals (mainly ECT signals). Reconstruction schemes based on conjugate gradient (CG) method of deterministic category and NN method, metaheuristic methods of stochastic category are developed and sizing of both artificial and natural cracks are performed by using measured signals. It is clarified through applications that a deterministic optimisation method is more efficient for treating simple cracks, while a stochastic way is prefer for defects of complicated geometry such as a stress corrosion crack and multiple cracks. In the crack modelling and parameterisation, an element of discontinuous material property is introduced to treat crack of arbitrary shape based on a given regular mesh. Several numerical models are proposed for natural cracks, which makes the reconstruction of some natural cracks become possible.

Sequential Monte Carlo Methods for Electromagnetic NDE Inverse Problems—Evaluation and Comparison of Measurement Models

Flaw profile estimation from measurements is a typical inverse problem in electromagnetic nondestructive evaluation (NDE). The application of recursive Bayesian nonlinear filters based on sequential Monte Carlo methods, in conjunction with measurement process models and a Markovian crack growth model, is a new approach for solving such inverse problems. The approach resembles the classical discrete-time tracking problem and is robust to the noisy measurement data. This paper reports a comparative study of the results of employing different measurement models in this Bayesian inversion framework. The results are evaluated on the basis of accuracy and computational cost.

Study of Lift-Off Invariance for Pulsed Eddy-Current Signals

Lift-off invariance (LOI) is getting much attention from researchers in the field of electromagnetic nondestructive evaluation (ENDE) because, at the LOI point, eddy-current signals for different lift-offs intersect and the signal amplitude is independent of the lift-off variance. We discuss our ongoing research into LOI, starting from an overview of the state-of-the art of pulsed eddy-current testing (PEC) systems and their use in the elimination of the lift-off effect. We have investigated LOI characteristics with respect to variation in the configuration of the PEC probe in a theoretical study, implemented by extended truncated region eigenfunction expansion (ETREE) modeling. We found that: 1) the LOI occurs when the first-order time derivative of the magnetic field signals are acquired from Hall sensors; 2) an LOI range instead of a single LOI point, when multiple lift-offs are introduced through both experimental and theoretical studies. The LOI range varies with the Hall sensor position in the probe assembly and the conductivity of the samples under inspection, which are important parameters for the design and development of PEC systems. Based on this understanding, we investigated new approaches using theoretical computation and multiple lift-off, or magnetic sensor arrays, for conductivity and lift-off estimation. Our study can be extended for design and development of multipurpose eddy-current sensor systems for surface form measurement and defect detection.

The AMDE project: 3D volumetric anomalies reconstruction by eddy current testing

The AMDE project (“Applicazioni di Metodi per Diagnostica Elettromagnetica”, in English “Applied Methods for Electromagnetic Evaluation”) is an Italian two-years national granted research project on electromagnetic non-destructive evaluation. This project involves five different research units located in Italy, about twenty researchers and ten among Ph.D. students and post-doc. Here we focus on the contribution of the AMDE project to the reconstruction of 3D volumetric defects in metallic plates as those used in aeronautical and aerospace industry. In particular, in this work we propose an efficient numerical model for evaluating the field due to volumetric anomalies and an inversion method based on the Total Variation Regularization. Numerical examples confirm the capability of the proposed strategy to reconstruct 3D volumetric defects.

A Recursive Bayesian Estimation Method for Solving Electromagnetic Nondestructive Evaluation Inverse Problems

Estimating flaw profiles from measurements is a typical inverse problem in electromagnetic nondestructive evaluation (NDE). This paper proposes a novel state-space approach for solving such inverse problems. The approach is robust in the presence of measurement noise. It formulates the inverse problem as a tracking problem with state and measurement equations. The state-space model resembles the classical discrete-time tracking problem. The model allows recursive Bayesian nonlinear filters based on sequential Monte Carlo methods to be applied in conjunction with numerical models that represent the measurement process (i.e., solution of the forward problem). We apply our approach to simulated eddy-current and magnetic flux leakage NDE measurements (with and without measurement noise) from known flaw shapes, and the results indicate the feasibility and robustness of the proposed method.

Fast analytical modelling for pulsed eddy current evaluation

Numerical simulations of electromagnetic non-destructive evaluation (ENDE) can be time-consuming in comparison to analytical methods which provide fast closed-form solutions to the ENDE problems. In this paper, the Truncated Region Eigenfunction Expansion (TREE) modelling is extended to solve problems of pulsed eddy current (PEC) evaluation from the traditional multifrequency eddy current. The Fourier transform is employed to make the TREE feasible for solutions to PEC problems in both time and frequency domains. Moreover, because PEC employs magnetic field sensors/arrays to quantify magnetic field, the magnetic field signals from solid-state magnetic field sensors have been simulated using the extended TREE. It has been found that the predicted signals using the extended TREE has good agreement with the experimental results. Consequently, the established model can not only offer an effective solution in terms of faster simulation time and higher computational accuracy, but also be used for PEC evaluation in industry and in the inverse process for exploring the structural and electrical information of stratified conductive specimens during real-time monitoring.

Pulsed electromagnetic methods for defect detection and characterisation

The magnetic flux leakage (MFL) method has very good defect detection and location capabilities, but defect sizing capabilities, especially for sub-surface defect characterisation, are limited. The pulsed magnetic flux leakage (PMFL) technique has recently been introduced and shown to have great potential for automated defect sizing for surface-breaking defects using time-frequency signal processing techniques, but sizing of sub-surface defects has proved problematic. In this paper, pulsed magnetic reluctance (PMR), a new electromagnetic (EM) non-destructive evaluation (NDE) technique, is introduced and incorporated into a dual PMFL/PMR probe for the characterisation of surface and sub-surface defects in ferromagnetic materials. Experimental results from a comparison study of the two techniques using variety of defects analysed using time-frequency analysis show that the techniques offer complementary information, with PMFL providing defect location data and data for the characterisation of surface defects and PMR offering sub-surface defect characterisation capabilities. The work concludes that integration of these inspection techniques in the new pulsed EM probe can provide enhanced defect characterisation capabilities for flux leakage-based inspection systems using relatively simple time-frequency signal processing techniques.

2419 高クロム鋼溶接継手の長時間高温強度に関する研究 : その8 電磁非破壊評価によるType-IV損傷検出性の検討(S13-2 高温材料・構造の強度と破壊(2),S13 高温材料・構造の強度と破壊)

The authors have discussed the feasibility of evaluation of Type IV damages of high Cr steel welds by electromagnetic nondestructive evaluation methods. As the first step, effects of isothermal-aging on magnetic properties were systematically examined. Ac magnetic properties at relatively high frequencies changes in accordance with Larson-Miller parameters of the isothermal-aging specimens of modified 9Cr-1Mo steel. Especially, ac losses at 100kHz correlate well with hardness of the specimens. Base on the findings, eddy current method was applied to the same samples. Signals linking the ac losses correlate well with hardness.

311 電磁非破壊評価を用いた片状黒鉛鋳鉄の黒鉛形態の推定(機械材料・材料加工I)

311 電磁非破壊評価を用いた片状黒鉛鋳鉄の黒鉛形態の推定(機械材料・材料加工I)

Shared issues of wavefield inversion and illustrations in 3-D diffusive electromagnetics

Electromagnetic non-destructive evaluation of complex objects means that one has to decipher data which result from their interaction with imposed sources. This task is crucial in civil, environmental and medical engineering, to quote obvious fields, as well as for safety and reliability of industrial processes of various kinds in key energy and transportation sectors, for example. This short contribution does not attempt to review the huge variety of themes and the many applications of the science of inversion, but aims at emphasizing a number of points that seem common enough to this science to be worthwhile to be reviewed. Two illustrations and a few main references thought of good interest among the ever increasing literature are given. To cite this article: D. Lesselier et al., C. R. Physique 6 (2005).

Electromagnetic Non-Destructive Evaluation of Fiberglass/Aluminum Laminates Using HTS SQUID Magnetometers

The aerospace and aeronautical industries pay much attention to improve flight safety of the airlines. In aircraft design it is important to couple low structural weight with high damage tolerance. For this reason, a new class of advanced composite materials, named Fiber/Metal Laminates (FML), which combine the best features of organic matrix composites and metals, are used. In this work, a nondestructive evaluation of FML specimens based on an eddy-current technique that uses an HTS SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The aim is to demonstrate that this technique is capable of detecting the presence of damage hidden by plastic deformation after impact events.

Development of novel NDE techniques and their significance in the COE program on the physics and chemistry of fracture and failure prevention

Development of novel NDE techniques and their significance in the COE program on the physics and chemistry of fracture and failure prevention

Robust solutions of inverse problems in electromagnetic non-destructiveevaluation

Non-destructive testing (NDT) is the application of physical measurementtechnology based on energy interaction with the material and its nonconformities.The material’s response is sensed by transducers and sensors which—in mostcases—scan the component and document the results in inspection images.However, NDT measures a physically defined quantity or even an intrinsicproperty.The difference between non-destructive evaluation (NDE) and NDT is in theinterpretation of the inspection data. NDE has to discuss the inspection results interms of quality elements and characteristics which are relevant to describe thefitness of the material for use. In the case of macroscopic defects these are thekind of defect (cracklike, globular) and its size and orientation to the main stressdirections; in the case of material property determination the parameters aremainly mechanical properties. Therefore, in NDE one has to solve inverseproblems.The solution of inverse problems based on mathematical procedures such asintegral equations is a strong developing discipline and most of the articlesprepared for this special issue of the journal have the objective of discussing thelatest state of the art in that field. However, practical NDE needs robust andquick solutions which are to be applied mainly online. Therefore, we present hereinversion procedures based on multiple linear regression algorithms applied toinspection data. We describe the calibration procedure to fit the free parametersof the model functions and give examples of practical applications in industry.

Theoretical investigation of eddy-current induction for nondestructive evaluation by superconducting quantum interference devices

An analysis of eddy-current induction is presented for applications in low-frequency electromagnetic nondestructive evaluation (NDE) using superconducting quantum interference devices (SQUID's). Analytical expressions are developed for the induced eddy currents, as well as the resulting magnetic fields produced by circular excitation coil above conducting plates of infinite and finite thicknesses. The in-phase (0/spl deg/) and quadrature-phase (90/spl deg/) components of the eddy-current density are plotted for the low-frequency excitations characteristic of SQUID NDE. The quadrature-phase eddy current has a peak value at the surface of conducting plates, while the in-phase eddy current is maximal at a characteristic depth in the conducting material. Also, both the quadrature- and in-phase eddy currents change signs at characteristic depths that depend on the skin depth. These features can be exploited in determining the depth of material defects. The expression for the magnetic field produced by an excitation coil above a conducting plate of finite thickness is then used to estimate the SQUID's response due to corrosion or variation in material thickness. The expressions derived here can be used to model the magnetic signature of localized defects.