Eddy Current Probe Research Articles

Detection of fiber waviness in CFRP using eddy current method

In this paper, a method of detecting fiber waviness in carbon fiber reinforced polymer (CFRP) using eddy current (EC) probe is proposed. The probe consists of a rectangular excitation coil and a rectangular reception coil that are perpendicular to each other. The excitation coil is along the designed fiber direction. Fiber waviness changes the direction of EC and generates a magnetic field component that is normal to the reception coil; thereby an output signal is obtained. The results of simulation and experiments show that the resolution of testing fiber direction using the proposed method is as small as 0.5° and fiber waviness can be detected according to the variation of scanning signal.

Nonlinear surrogate synthesis of the surface circular eddy current probes

Nonlinear surrogate synthesis of the surface circular eddy current probes

The Eddy Current Method of Alloy Drill Pipes Wall Thickness Evaluation: Impact Analysis

The dependences of the surface eddy current probe added voltage at the interaction of the probe magnetic field with an aluminum pipe from the following main interference factors are determined: the pipe wall thickness, the gap between the probe and the surface of the pipe, the electrical conductivity of the material, the curvature of the pipe wall, the presence of areas with a smooth thickness change of the wedge character and a local spherical thinning, axis misalignment with respect to the pipe surface, the lateral misalignment of the probe axis. The problem is solved with the help of the finite element method (FEM). These data are consistent with the experimental results.

Study of Interaction of Eddy Current Probes and Delamination in Multidirectional CFRP

This paper describes the physics of the interaction of the eddy current probe and the delamination in multidirectional carbon fiber reinforced polymer (CFDR). Currently, there is an opinion that eddy current signals obtained due to delamination in multidirectional CFRP are caused by the redistribution of the vertical eddy current arising from the excitation of eddy currents in the sample by a rectangular coil whose surface is orthogonal to the surface of the sample. The analysis performed by us shows that the possibility of creation and deformation of the vertical eddy current is very questionable, and that the observed eddy current signals associated with the delamination are most likely caused by carbon fiber plies misalignment towards the sample surface. In this paper was compare eddy-current signals from the delamination in CFRP in samples where the existence of vertical eddy current is possible in theory and in samples where this is not possible. The obtained signals had similar measurements, and this indirectly indicates the doubtfulness of the hypothesis of the delamination detection in CFRP samples due to vertical eddy current.

An Approach to Eddy-Current Evaluation of the Structural State in a Cast Aluminum–Silicon Alloy Subjected to Surface Laser Heat Treatment

The effect of surface laser heat treatment on the eddy-current parameters of the cast Al–6.34Si–0.32Mg alloy has been studied at excitation frequencies of f = 6–136 kHz. It has been established that the laser heat treatment affects both the amplitude A and the phase angle φ of the eddy-current probe signal. The observed changes in the eddy-current parameters of the laser-treated alloy are caused by the changes in the structural state of the alloy, particularly, by the high dispersity of the structure, increased content of alloying elements in the solid solution, and residual stresses resulting from accelerated cooling under laser melting. The depth of the molten zone and the homogeneity of the structure at different depths can be estimated by measuring the amplitude A, whereas the presence and level of residual stresses can be estimated by measuring the phase angle φ at different probe excitation frequencies. The results clearly show the advantage of separate measurements of the amplitude A and the phase angle φ from the perspective of eddy-current evaluation of the structural state of the laser-treated alloy.

Estimating POD of a screening technique for cracks about ferrous fasteners without fastener removal

A study was conducted to estimate the Probability of Detection (POD) of a screening technique for samples representative of lap joints in wing structure of the P-3 Orion airframe containing EDM notches in the bottom of the top layer and the top of the second layer radiating from holes containing ferrous fasteners. It was assumed that the defects made up only a small fraction of the data (<= 5%) as would be normal in a damage tolerant design. A novel pulsed eddy current probe and robust cluster analysis were used to provide blind detection of the notches without removal of the ferrous fasteners. Detection could be confirmed using traditional bolt-hole eddy current after fastener removal at that site. Statistical simulations were used to explore the effects of sample size and number of defects in a sample. Using a nominal false call rate of 15% (actual ∼10%), the estimated a90/95 was better than 2.3 mm (0.09 inch) for these data sets. This represents a marginal probability as the results indicate that other variables affect the estimated POD. Sample statistics can be used to show that the assumptions of the technique (i.e. very small fraction of the fasteners have associated defects) are not violated and that the inspector performed the inspection in a suitable manner.

Numerical study on corrosion profile estimation of a corroded steel plate using eddy current

This article presents corrosion profile estimation as a method to determine the extent of corrosion in steel members having corroded exterior, with or without protective cover, when the only side accessible to the eddy current probe is highly uneven. A high frequency eddy current method is proposed to estimate the corrosion profile of a steel plate directly from the probe lift-offs regardless of varying plate thickness. The three-dimensional, numerical simulations were carried out in the FEM software, COMSOL Multiphysics 5.2a to verify the suitability of this method. A parametric study is conducted to determine the effect of coil height, diameter, their ratio and tilt angle of reflection probe on the estimation accuracy of a triangular notched profile, representative of corrosion, whereby a geometrically optimized probe is obtained. It is then employed to determine the corrosion profile of a corroded steel plate with and without protective cover. The estimated corrosion profiles show good agreement with the actual profile measured by laser displacement meter, confirming the sufficiency of proposed method.

Design and optimisation of mutual inductance based pulsed eddy current probe

High lift-off inspection arising from thick insulation and requirement to protect probe from weld zones are challenges to pulsed eddy current (PEC) testing. In traditional PEC probe with fixed coil gap, weakening interaction between probe and test sample as lift-off increases reduces sensitivity. To analyse this influence, numerical simulation and experiments on design and optimisation of driver-pickup PEC probes are carried out. Results validate that both coil gap and lift-off have significant effects on resultant mutual inductance of driver-pickup PEC probes above test samples. In addition, the probe sensitivity is enhanced at a higher lift-off when coil gap exceeds a certain value. The increase in detection lift-off with coil gap could be optimised.

Eddy Current Testing Probe Based on Double-Coil Excitation and GMR Sensor

The development of eddy current nondestructive techniques and instruments is moving toward new challenges in detecting buried and smaller defects and minimizing the amplitude of excitation currents. The smaller the size of the detected defect, the greater is the diagnostic capability of these techniques. Moreover, the lower the excitation current required, the longer the battery discharge time of the portable instruments, the greater the possibility of implementing broadband excitation strategies with reliable results. This feature is also important when portable instruments with array of probes have to operate for a large amount of time. Following the actual trends based on the use of double-coil excitations, this paper proposes the investigation of the performance of these kinds of probes, when small and buried defects are involved, and low amplitudes of the excitation current are adopted. To allow these activities a suitable double-coil-based excitation probe has been assembled. The obtained performance has been also compared with a traditional single-coil excitation probe based on the same sensing element. The experimental analysis demonstrated the appreciable performance of the proposed solution in a number of test cases.

Hybrid GMR/IR probe to reduce the effects of lift-off

Eddy current testing technique is being utilized in engineering, such as in nuclear steam pipe, aircraft and gas/oil pipeline, due to its sensitivity to small cracks and subsurface defects, immediate results, environmental friendliness, and use in examining complex sizes and shapes of substances. However, the lift-off noise due to irregular inspected materials surface, varying coating thicknesses, or movement of transducers extremely limits the implementation of eddy current testing in a non-disastrous testing which impacts the measure of defect depth on the conductive material. In this paper, a study on hybrid giant magneto-resistance/infrared probe is proposed to minimize the influence of lift-off for detecting the depth defect. The giant magneto-resistance reads the magnetic field which reflects any defect inside the pipeline, and infrared sensors read the movement of each giant magneto-resistance inside the pipeline. The error compensation technique depends on Mamdani fuzzy which examines the interaction that exists between the peak value of giant magneto-resistance and the infrared sensor signal. The eddy current testing inspection system includes details of the giant magneto-resistance–eddy current probe design and instrumentation of the error compensation technique. The measurement method is based on alternating current supply with 30 kHz frequency to ensure that the crack signals are clearly displayed. The proposed method is verified experimentally, and the result shows that the impact of lift-off noise is highly reduced in the eddy current testing technique and enhances the sensor accuracy. The depth defect error caused by 1 mm lift-off is reduced to 7.20%.

DEVELOPMENT OF EXCITATION STRUCTURE RBF-METAMODELS OF MOVING CONCENTRIC EDDY CURRENT PROBE

Introduction. The work is devoted to metamodels creation of surface circular concentric eddy current probe. Formulation of the problem. In the problem of surface circular concentric eddy current probe synthesis in the general formulation, apriori given desired eddy currents density distribution in the control zone was used. The realization of the optimal synthesis problem involves a multiple solution to the analysis problem for each current structure of numerical calculations excitation, which are very costly in terms of computational and time costs, which makes it impossible to solve the synthesis problem in the classical formulation. By solving the critical resource intensiveness problem, there is the surrogate optimization technology using of that uses the surface circular concentric eddy current probe metamodel, which is much simpler in realization and is an approximation of the exact electrodynamic model. Goal. Creation of surface circular concentric eddy current probe RBF-metamodels, which can be used to calculate eddy currents density distribution in the control zone and suitable for use in optimal synthesis problems. Method. To develop an approximation model, a mathematical apparatus for artificial neural networks, namely, RBF–networks, has been used, whose accuracy has been increased with the help of the neural networks committee. Correction of errors in the committee was reduced by applying the bagging procedure. During the network training the regularization technique is used, which avoids re-learning the neural network. The computer experiment plan was performed using the Sobol LPt–sequences. The obtained multivariable regression model quality evaluation was performed by checking the response surface reproducibility correctness in the entire region of variables variation. Results. The modelling of eddy currents density distribution calculations on exact electrodynamic mathematical models in the experimental plan points are carried out. For the immovable and moving surface circular concentric eddy current probe, RBF–metamodels were constructed with varying spatial coordinates and radius. Scientific novelty. Software was developed for eddy currents density distribution calculation in the surface circular concentric eddy current probe control zone taking into account the speed effect on exact electrodynamic mathematical models and for forming experiment plan points using the Sobol LPt–sequences. The geometric surface circular concentric eddy current probe excitation structures models with homogeneous sensitivity for their optimal synthesis taking into account the speed effect are proposed. Improved computing technology for constructing metamodels. The RBF-metamodels of the surface circular concentric eddy current probe are built and based on the speed effect. Practical significance. The work results can be used in the surface circular concentric eddy current probe synthesis with an apriori given eddy currents density distribution in the control zone.

Experimental and Analytical Investigation of Short Squeeze-Film Damper (SFD) Under Circular-Centered Orbit (CCO) Motion

Modern rotating machines operate at higher shaft speeds, crossing a few bending critical speeds, which often induce large dynamic loads on the bearing supports that may increase the rotor orbital whirl motion. Accurate prediction of squeeze-film damper (SFD) forces is the key issue for designers to arrive at a suitable design. An experimental setup was developed with eccentric shaft to find the damper forces. Submerged type damper with relatively large clearance was considered for the present work. It results in higher gap Reynolds number (Re) which varies from 1.5 to 15 in the present case. Four force sensors are used to measure the damper forces and two eddy current probes were used to measure the damper orbit. Circular-centered orbit (CCO) of eccentricity ratio (e) 0.176 was used in the present work. Theoretical modeling of SFD forces is considered with viscous, inertial, temporal contributions under laminar and turbulent conditions. Modified Reynolds equation with short damper approximation is used to derive the SFD forces for 2π- film. Fourier coefficients of measured forces and displacements are estimated and used to extract the 1× components and phase information. Radial and tangential forces were calculated from the measured total forces to find the contributions of viscous and inertial forces. Experimental forces are compared with theoretically predicted forces and they are in good agreement with the experimental results.

Investigation of aluminum alloys by using subminiature eddy current probes

On the basis of the eddy current probe(ECP) of a transformer type the measuring system that allows to search for defects in aluminum alloys is developed. The main technical data on the used eddy current probe and measuring system are given. The results of experiments obtained using different designs of the measuring system on two plates of duralumin D16T are presented. These dependences allow us to assess the quality of the alloys under study.

A remote field eddy current probe for outside inspection of pipe defects

A remote field eddy current probe for outside inspection of pipe defects

Fast computation of the response of any 3D Eddy Current probe scanning a 3D stratified conductor characterized by a set of arbitrary interfaces of complex shape

Fast computation of the response of any 3D Eddy Current probe scanning a 3D stratified conductor characterized by a set of arbitrary interfaces of complex shape

Design of Eddy Current Testing Probe for Surface Defect Evaluation

Early detection of defects in metallic components used in infrastructure is crucial to ensure their safety and reliability. This paper presents a development of a small eddy current testing (ECT) probe for evaluation of sub-millimetre surface defects. The ECT probe is developed in a planar differential using sensitive anisotropy magnetoresistance sensors, and the signal amplification is achieved by a home-made instrumentation amplifier. The developed ECT probe is evaluated by performing phase sensitive measurement of the magnetic responses of sub-millimetre surface slits at the excitation field of 200 Hz and 10 kHz. Compared to the real component of the magnetic response, the imaginary component can be used to identify the existence and position of the slits based on the signal intensity change caused by the induced eddy current. The spatial distribution of the magnetic response measured by the ECT probe can be used to estimate the dimension of the slit. It is expected that the developed ECT probe can be utilised for assessment of sub-millimetre surface defect.

Static and Dynamic Coefficient Measurements for a Thrust Collar Used in an Integrally Geared Compressor

This paper introduces a test facility specifically designed to measure the axial stiffness and damping coefficients of an oil-lubricated thrust collar (TC). The geometry, load, and speeds of the test facility are representative of a production integrally geared compressor (IGC). Separate electric motors spin the shafts according to an assumed gear ratio; a pneumatic air piston loader provides a noncontacting, static thrust force; a remotely controlled impact hammer delivers a perturbation force; and eddy-current motion probes record the resulting vibration. The paper uses a one degree-of-freedom (1DOF) axial motion model that neglects the static and dynamic stiffness of the bull wheel (BW) and presents estimates of the TC oil-film dynamic coefficients for pinion spin speeds between 5 and 10 krpm, and static loads between 200 and 400 N, using time-domain (log-dec and damped period) and static load-deflection techniques. The measurements show that the TC oil-film develops appreciable stiffness (tens of MN/m), and the 1DOF model used here is inadequate for higher loads. Axial runout on the interfacing surfaces of the test facility TC and BW complicates parameter identification, but time-domain averaging effectively attenuates the runout while preserving the transient vibration that results from the impact hammer. Measurements of the TC oil-film stiffness, damping, and virtual mass coefficients are useful to machinery original equipment manufacturers (OEMs) or end-users seeking to predict or diagnose subsynchronous vibration in their machine that might be TC-related.

An accurate localization system for Nondestructive testing based on magnetic measurements in quasi-planar domain

Localization of eddy current probes in Nondestructive Testing allows merging the defect detection with the information about defect positions. Typically, this task requires the usage of additional and costly position measurement systems or software assisted handlers in controlled laboratory conditions. However, many of these tests require free hand movements of the eddy current probes. In addition, in many industrial applications low cost is a stringent requirement. This paper proposes a novel solution to address the considered issues. In particular, the paper describes the usage of a magnetic 2D wireless localization method, able to track the probe position during the execution of Nondestructive Tests. To the best of our knowledge, such approach is novel and promises to provide localization information in Nondestructive Testing by means of low-cost hardware. Moreover, it is characterized by a light computational burden, since it reuses most of the equipment already needed for the test itself. Preliminary results, proving the suitability of a real time simultaneous testing and localization system, are reported in this paper.

EDDY Current Array Probes and Applications

EDDY Current Array Probes and Applications

Eddy-Current System for Testing Inner Diameter of Pipes

We propose a method for eddy-current testing of the inner diameter of electroconductive pipes. The design of an eddy current transducer is described, as well as an algorithm for converting measurement information signals and the block diagram of a system for testing the inner diameter of pipes that allows testing under conditions of significant radial displacements of the eddy current probe inside the pipe. The effectiveness of the proposed engineering solutions is evaluated.