Effects of angular variation on split D differential eddy current probe response

Mooers, Ryan D.; Aldrin, John C.

doi:10.1063/1.4940559

Cited by 6 publications

(3 citation statements)

References 6 publications

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“…In addition, the rotation of the probe is finely adjusted in order to set the separation surface of the D-cores parallel to the notch axis. Although it is known that achieving a perfect alignment for the probe's rotation is not possible, but according to a study on angular variations of a split-D probe by Mooers and Aldrin, small angular rotations of the probe between − 10 and 10 degrees does not affect either shape or the amplitude of the probe's signal [30]. The perpendicularity of the probe with respect to the aluminum block's surface has been verified by scanning a surface notch.…”

Section: Impedance Measurement Of a Commercial Split-d Coilmentioning

confidence: 99%

Finite Element Modelling of a Reflection Differential Split-D Eddy Current Probe Scanning Surface Notches

et al. 2020

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Differential eddy current probes are commonly used to detect shallow surface cracks in conductive materials. In recent years, a growing number of research works on their numerical modelling was conducted since the development of analytical or semi-analytical models for such a sensor may be prone to intractable complications. In this paper finite element modelling (FEM) has been employed to simulate the interaction of a reflection differential split-D probe with surface electrical discharge machined (EDM) notches in 3-dimensional (3-D) half-space. In order to attain a better insight into the correct setup of the FEM parameters, a simple multi-turn cylindrical absolute coil has also been modelled. The outcome generated through the simulated scan of this absolute coil over a surface notch in aluminum is validated with existing experimental impedance data taken from the literature. Parameters contributing to reliable FEM simulation results, such as maximum mesh size, mesh distribution, the extent of the surrounding air domain and conductivity of the air are investigated for the 3-D modelling of both absolute and differential probes. This study shows that the simulation results on a commercial reflection differential split-D surface pencil probe closely estimate the experimental measurements of the probe's impedance variations as it scans three EDM notches having different depths in aluminum. The simulation results, generated by Comsol Multiphysics FEM package (COMSOL I, COMSOL multiphysics reference manual, version 5.3, COMSOL AB, 2018, www.comsol.com), for the cases of absolute and differential probes are checked for their extent of validity.

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Section: Impedance Measurement Of a Commercial Split-d Coilmentioning

confidence: 99%

Finite Element Modelling of a Reflection Differential Split-D Eddy Current Probe Scanning Surface Notches

et al. 2020

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“…Recent work by Ryan Mooers has investigated this challenge through several benchmarking studies [9][10]. More mesh resolution appears to be needed (relative to the base VIC-3D® model for probes with normal orientation) with the core/coil portion of the probe tilted near the surface.…”

Section: Progress On Full Model-based Calibration Approachmentioning

confidence: 99%

Model-based inverse methods for sizing surface-breaking discontinuities with eddy current probe variability

Aldrin¹,

Shell

Oneida

et al. 2016

AIP Conference Proceedings

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Abstract. The objective of this work is to demonstrate and validate model-based inversion techniques to characterize length, depth, width and orientation of surface-breaking cracks using eddy current NDE under varying probe conditions. A series of parametric studies of probe characteristics are presented for a fixed set of well-characterized flaws with varying length, depth, opening width and orientation angle. Results show inversion performance differences between probes with the same design specifications. Inversion results were also evaluated for a probe that was selectively controlled for varying probe liftoff, varying tilt in two directions, and orientation. Certain levels of probe tilt and liftoff were found to degrade the performance of the inversion technique. By using a model calibration process that incorporates the matching probe calibration data, better inversion results can be achieved, to a limited degree. There is a need to more appropriately adapt the model through the calibration fit to compensate for varying probe tilt and liftoff. Results are presented for a model transform approach, evaluating scale and phase terms based on the best model fit with the calibration data. The results for certain severe cases of liftoff were improved using the transformed model; however, it does not address all probe conditions. Future work is proposed to use a full model-based transformation approach using more comprehensive meta-model representations.

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“…This is an important challenge for model-based inversion crack sizing techniques, to be robust to the varying characteristics of eddy current probes found in the field [1][2]. In this paper, a model-based calibration process is introduced that estimates the state of the probe.…”

mentioning

confidence: 99%

Model-based probe state estimation and crack inverse methods addressing eddy current probe variability

Aldrin¹,

Oneida

Shell

et al. 2017

AIP Conference Proceedings

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Recent work on model-based inverse methods with eddy current inspections of surface breaking discontinuities has shown some sizing error due to variability in probes with the same design specifications [1]. This is an important challenge for model-based inversion crack sizing techniques, to be robust to the varying characteristics of eddy current probes found in the field [1][2]. In this paper, a model-based calibration process is introduced that estimates the state of the probe. First, a carefully designed surrogate model was built using VIC-3D ® simulations covering the critical range of probe rotation angles, tilt in two directions, and probe offset (liftoff) for both tangential and longitudinal flaw orientations. Some approximations and numerical compromises in the model were made to represent tilt in two directions and reduce simulation time; however, this surrogate model was found to represent the key trends in the eddy current response for each of the four probe properties in experimental verification studies well. Next, this model was incorporated into an iterative inversion scheme during the calibration process, to estimate the probe state while also addressing the gain/phase fit and centering the calibration notch indication. Results are presented showing several examples of the blind estimation of tilt and rotation angle for known experimental cases with good agreement within +/-2.5 degrees. The RMS error was found to be significantly reduced by fitting the probe state and, in many instances, probe state estimation addresses the previously un-modelled characteristics (model error) with real probe inversion studies. Additional studies are presented comparing the size of the calibration notch and the quality of the calibration fit, where calibrating with too small or too large a notch can produce poorer inversion results. Once the probe state is estimated, the final step is to transform the base crack inversion surrogate model and apply it for crack characterization. Because of the dimensionality of this problem, simulations were made at a limited set of select flaw sizes with varying length, depth and width, and an interpolation scheme was used to address the effect of the probe state at intermediate solution points. Using this process, results are presented demonstrating improved crack inversion performance for extreme probe states.Acknowledgements:

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Effects of angular variation on split D differential eddy current probe response

Cited by 6 publications

References 6 publications

Finite Element Modelling of a Reflection Differential Split-D Eddy Current Probe Scanning Surface Notches

Finite Element Modelling of a Reflection Differential Split-D Eddy Current Probe Scanning Surface Notches

Model-based inverse methods for sizing surface-breaking discontinuities with eddy current probe variability

Model-based probe state estimation and crack inverse methods addressing eddy current probe variability

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