Open crack depth evaluation using eddy current methods and GMR detection (original) (raw)
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Evaluation of crack depth using eddy current techniques with GMR-based probes
2015 IEEE Metrology for Aerospace (MetroAeroSpace), 2015
This paper presents experimental and simulated results obtained using the eddy current nondestructive method to conclude about the depth of linear cracks machined on an aluminum plate. Experimental tests were performed with a sinusoidal excitation field of fixed-amplitude and with a giant magnetoresistance-based sensor to measure the resultant magnetic field on the plate surface. To validate and better insight the experimental results, numerical simulations have been carried out with a commercial program for conditions similar to the experimental case studies. A scheme to infer about crack depth is proposed.
Eddy-current non-destructive testing system using a magnetic sensor based on GMR
Detecting the cracks is a major challenge in the development of Eddy Current (EC) Non-Destructive Testing (NDT). In fact, the detection sensitivity of EC-NDT depends on the interaction between the crack characteristics and the EC formed in the materials. The induced currents are primarily generated along a single direction in the tested sample. This paper presents a excitation method for generating a ac magnetic field and, consequently, eddy currents. This method significantly improves the detection of cracks of two different kind of material (non magnetic conductive material and ferromagnetic material). The magnetic flux density signature of the defect is studied using a 2D Finite Element Model FEM.
Eddy Current Testing of Thick Aluminum Plates with Hidden Cracks
In this paper we present theoretical analysis which gives the possibility to determine optimum excitation frequencies in eddy current examination of thick aluminum plates. A computer controlled non-destructive testing system and a probe with a magnetoresistive sensor were utilized in laboratory tests. Experiments with specimens containing hidden cracks were carried out for a wide spectrum of frequencies. The optimum operating frequencies achieved from the experiments are in a very good agreement with those obtained by using theoretical analysis. Application of the optimum frequencies makes it possible to detect shallow cracks located on the reverse side of the specimens. Detection of a 15 % crack in a 10 mm thick plate made of aluminum and a 20 % crack in a 20 mm thick plate has been confirmed.
Identification of crack depths from eddy current testing signal
IEEE Transactions on Magnetics, 1998
This paper demonstrates the identification of crack depths using signals obtained from eddy current testing (ECT). The identification method is based on finite elements with the pre-computed unflawed database approach and a meshless crack representation technique, and parameter estimation in non-linear problems. Four different cracks are estimated by using laboratory data. Index Terms-Eddy current testing, steam generator tubes, inverse problems, finite element methods, reduced magnetic vector potentials, pre-computed unflawed database approach, meshless crack representation technique, trust region method.
Determination of linear defect depths from eddy currents disturbances
2014
One of the still open problems in the inspection research concerns the determination of the maximum depth to which a surface defect goes. Eddy current testing being one of the most sensitive well established inspection methods, able to detect and characterize different type of defects in conductive materials, is an adequate technique to solve this problem. This paper reports a study concerning the disturbances in the magnetic field and in the lines of current due to a machined linear defect having different depths in order to extract relevant information that allows the determination of the defect characteristics. The image of the eddy currents (EC) is paramount to understand the physical phenomena involved. The EC images for this study are generated using a commercial finite element model (FLUX). The excitation used produces a uniform magnetic field on the plate under test in the absence of defects and the disturbances due to the defects are compared with those obtained from experimental measurements. In order to increase the limited penetration depth of the method giant magnetoresistors (GMR) are used to lower the working frequency. The geometry of the excitation planar coil produces a uniform magnetic field on an area of around the GMR sensor, inducing a uniform eddy current distribution on the plate. In the presence of defects in the material surface, the lines of currents inside the material are deviated from their uniform direction and the magnetic field produced by these currents is sensed by the GMR sensor. Besides the theoretical study of the electromagnetic system, the paper describes the experiments that have been carried out to support the theory and conclusions are drawn for cracks having different depths.
Russian Journal of Nondestructive Testing, 2020
The study of 3D eddy current non destructive testing system for cracks characterization using finite element method requires a great amount of computing time and memory space. In this article, we have validated the developed model and then determined directly the crack length by analyzing the complete signal. Afterwards, we have extracted from the complete sensor sweep signal the maximal amplitude that we have exploited to estimate the crack depth.
Estimation of the defects dimension with a GMR eddy current sensor
This paper presents an experimental system to detect defects in aluminum by eddy currents using a GMR sensor. In three plates of aluminum were constructed defects of 0.6, 1 and 1.4 mm of the width and depths of 0.5, 1, 1.5, 2, 4, 6 and 8 mm, the defects were scanned with the sensing axis perpendicular to the defect length in ten times. The parameters DV and DX were extracted from output voltage signal. Results of this work show that the output voltage of the GMR sensor depends of the width and the depth of the defect. DX depends only on width when the depth of defect is equal or greater than 4 mm. Fitting functions were proposed for the experimental values of DV and DX, these functions show the relationship between the physical dimensions of the defects and parameters DX and DV. Also studied the dependence of DV with the filling factor of the excitation coil.
An Eddy Current Nondestructive Method for Crack Detection in Multilayer Riveted Structures
Instrumentation Mesure Métrologie, 2019
It is a challenging task to detect the hidden cracks in multilayer riveted structures in a nondestructive manner. This paper puts forward an eddy current nondestructive method for crack detection in such structures based on the electric conductivity of the rivets. Specifically, an eddy current sensor was designed with a ferrite core coil to evaluate the surface and inner defects of different layers. The magnetic phenomena during the detection process was simulated based on the magnetic potential and the scalar electrical potential, and the magnetic potential vector was solved by finite-element method. The proposed method was compared with the eddy current detection method without considering rivet conductivity through an experiment on a three-layer riveted aluminum structure. The length and position of each defect on each layer were changed in the experiment. The results show that the proposed method achieved better accuracy than the contrastive method, and its sensitivity depends on two issues: the position of the defect relative to the separation of the layers and the length of the defect relative to the length of the rivet head. The research results are of great significance for nondestructive testing of multilayer riveted structures in many fields.
Detection and measurement of surface cracks in ferromagnetic materials using eddy current testing
NDT & E International, 2006
Eddy current testing is used to detect and quantify defects in electric conductive materials. Defects investigated are specifically mechanical, chemical and microstructural heterogeneities. In this scope, artificial defects simulating superficial cracks have been achieved in order to establish an eventual relationship between the orientation, the shape and the size of the defect in one hand, and the signature that it generates in the impedance plane on the other hand. We determine in the first stage the operating conditions for the minimization of all signals that may perturb the crack signal such as the background one. We have been able to detect easily a surface crack on ferromagnetic steel in a large range of the frequency. Curves allowing the discrimination between signals corresponding to the presence of cracks and those corresponding to a lift-off have been established. The limit depth has as well been determined and we found that this limit has no relationship with the depth of penetration of the eddy current. The operative parameters such as the diameter and the working mode of the probe, the excitation frequency and the setting of the measurement equipment have been optimized for the testing of the quality and the reliability of critical ferromagnetic steel parts.
A Study of the Automated Eddy Current Detection of Cracks in Steel Plates
Journal of Nondestructive Evaluation, 2019
Applying life estimation approaches to determine in-service life of structures and plan the inspection schedules accordingly are becoming acceptable safety design procedures in aerospace. However, these design systems shall be fed with reliable parameters related to material properties, loading conditions and defect characteristics. In this context, the role of non-destructive (NDT) testing reliability is of high importance in detecting and sizing defects. Eddy current test (ECT) is an electromagnetic NDT method frequently used to inspect tiny surface fatigue cracks in sensitive industries. Owing to the new advances in robotic technologies, there is a trend to integrate the ECT into automated systems to perform NDT inspections more efficiently. In fact, ECT can be effectively automated as to increase the coverage, repeatability and scanning speed. The reliability of ECT scanning, however, should be thoroughly investigated and compared to conventional modes of applications to obtain ...