Characterization of defects on rivets using a eddy current technique with GMRs (original) (raw)
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Hybrid of Eddy Current Probe Based on Permanent Magnet and GMR Sensor
Journal of Telecommunication, Electronic and Computer Engineering, 2018
The eddy current testing (ECT) is used to inspect a material to determine its properties without destroying its utility. The applications include detection of flaws in aircrafts, pipeline, etc. An ECT is a weak sensitivity to a subsurface defect. Applications of giant magnetic sensors (GMR) are increasingly applied to the measurement of weak magnetic fields related to the currents they cause. In this paper, GMR sensor with magnet bar (permanent) is utilized. The proposed probe system is utilized to study the impact of the width and depth defect on the signal of eddy current testing. The maximum depth of flaw in a mild steel can be revealed by using this probe. The graph of the difference between the peak amplitude and the penetration depth of each slot of a different width of the two bands of mild steel shows the increase of the signal for each slot and flat above 3mm. The experimental result proves the inability of a PMGMR probe to detect a defect at a depth of 3mm on a surface def...
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.
Induction defectoscope based on uniform eddy current probe with GMRs
2010 IEEE Instrumentation & Measurement Technology Conference Proceedings, 2010
Defect detection in conductive plates represents an important issue. The present work proposes an induction defectoscope that includes a uniform eddy current probe with a rectangular excitation coil and a set of giant magnetoresistance sensors (GMR). The excitation current, the acquisition of the voltages delivered by the GMR and the signal processing of the acquired signal are performed by a real-time control and processing unit based on a TMS320C6713 digital signal processor (DSP). Different tests were carried out regarding the excitation coil position versus crack orientation and also regarding the GMR position inside the coil and the best response concerning the crack detection for a given aluminum plate specimen. Embedded software was developed using a NI LabVIEW DSP module including sinusoidal signal generation, amplitude and phase extraction using a sine-fitting algorithm and GUI for the induction defectoscope. Experimental results with probe characterization and detection of defects were included in the paper.
2017
In eddy current nondestructive testing (EC-NDT) of a multilayer riveted structure, rotating current excitation, generated by orthogonal coils, is advantageous in providing sensitivity to defects of all orientations. The signal of a defect is not only a function of its size but also of the geometrical features in vicinity to the rivet such as edges, adjacent rivets and properties of the layered structure. Numerical models can be used to provide fast and accurate estimates of defect signals. In this paper the sensitivity of the eddy current system with rotating current excitation and GMR sensors is evaluated by considering the effect of rivet permeability, lift-off, thickness of first layer as well as defect orientation related to adjacent rivets and edges on the signal measured. A numerical model capable of simulating these combinations of defect and test geometry parameters at an acceptable computation time is used. A meta-model is developed based on these simulation results and utilized for sensitivity evaluation.
Characterization and implementation of a GMR based probe for eddy current testing
International Journal of Applied Electromagnetics and Mechanics, 2008
The aim of this work is to describe an eddy current non-destructive testing system employing Giant Magnetoresistive (GMR) sensors. GMR sensors are solid state devices capable of measuring the magnetic flux density. The use of GMR sensors in the framework of eddy current testing is motivated by their intrinsically high sensitivity, large bandwidth and low cost. This paper is specifically focused on the development of a GMR based probe integrated into an eddy current testing system for detecting the presence of millimeters size cracks in highly conductive materials such as Aluminum.
Standard Pulsed Eddy Current Systems, as RTD-INCOTEST© equipment, use receiver coils to measure eddy current decay in conducting objects. Advantages of full coils, as sensor for the eddy current, are its simple construction and the possibility of eddy current focussing. But, some disadvantages are the high induction voltage due to a large pulsed signal, the large sensor area and the low coil's sensitivity especially at large times. Some of these disadvantages can be avoided by using a magnetic-field sensor instead of a coil and some advantages also appear. Recent developments in Improved GMR Magnetometer open a new possibility to measure the decay by means of magnetic-field measurement. The present paper focuses on recent theoretical and practical investigations made by RTD and his partners. The measurement method is presented and discussed in comparison with the theoretical signal behaviour. Experimental features are investigated and the practical feasibility of the technique ...
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.
GMR based eddy current sensing probe for weld zone testing
2009
The detection of flaws in the weld zone of conductive plates is an important issue and, in this field, different solutions using eddy current probes are mentioned in the literature. However, when eddy current pancake probes are used, it is difficult to detect the flaws or the welding non-uniformities due to the lift-off effects. Thus, in the present work we present a novel uniform eddy current probe architecture based on a tangential excitation coil with a rectangular geometry and highly sensitive giant magnetoresistances (GMR). The induced magnetic field is measured using a GMR sensor fixed on the axis midpoint inside the coil. The sensor sensitive axis is perpendicular to the excitation coil axis in order to measure only the induced magnetic fields caused by the presence of flaws. We developed an automatic testing system to characterize the sensor and to perform tests on aluminum plate specimens with flaws included in the weld zone.