Quantitative interpretation of magnetic field measurements in eddy current defect detection

PhD ThesisFor many years, the theoretical and experimental study of eddy current non-destructive evaluation (NDE) has been conducted separately, as most models were not suited to practical industrial applications. The aim of this work is to bridge this gap by investigating the relationship between magnetic fields and defects using both modelling and experimental study and to link these results to quantitative NDE. In this work, 3D FEM numerical simulations are used to predict the response of an eddy current probe being scanned over the area of a defect and understand the underlying change in magnetic field due to the presence of the defect. Experimental investigations are performed to study the feasibility of the proposed magnetic field measurement techniques for defect detection. This experimental work investigates the inspection of both surface and subsurface defects, the use of rectangular (directional) probes and the measurement of complex magnetic field values, as the response in these cases has been found to have a greater correlation with the shape of the defect being studied. As well as the detection of defects, both frequency spectrum and transient information from pulsed eddy current responses are used to reconstruct the profile (depth and width) of a slot shaped defect. The work concludes that the use of magnetic field measurements provides useful information for defect detection and quantification. This will have applications in both industrial and research areas, including visualisation of defects from magnetic field measurements, which can be applied to the monitoring of safety critical components.Engineering and Physical Sciences Research Council

Magnetic-Field-Based 3D ETREE Modelling for Multi-Frequency Eddy Current Inspection

International audienceMore and more solid-state magnetic field sensors such as Hall devices are used in eddy current inspection (EC) to acquire magnetic field signals. This work extends the previous analytical model, i.e. 2D Extended Truncated Region Eigenfunction Expansion (ETREE) of EC, and focuses on establishment of 3D ETREE of multi-frequency eddy current inspection (MFEC) on stratified conductors, while taking into account the solid-state magnetic field sensors for field quantification and rectangular coils for field excitation. 3D Finite Element Modelling (FEM) and a hybrid modelling are adopted for verification of the established model. It has been noticed that the 3D ETREE implements the fast and accurate computation of magnetic field signals of MFEC. Following that, the directional characteristics of EC with rectangular excitation coils are investigated, which reveals that the coil width contributes more to the measurement sensitivity than the coil length, and benefits the evaluation of defects and anisotropic conductivity profile of conductors in the follow-up study

Magnetic-field-based 3D ETREE modelling for multi- frequency eddy current inspection

Abstract. More and more solid-state magnetic field sensors such as Hall devices are used in eddy current inspection (EC) to acquire magnetic field signals. This work extends the previous analytical model, i.e. 2D Extended Truncated Region Eigenfunction Expansion (ETREE) of EC, and focuses on establishment of 3D ETREE of multi-frequency eddy current inspection (MFEC) on stratified conductors, while taking into account the solid-state magnetic field sensors for field quantification and rectangular coils for field excitation. 3D Finite Element Modelling (FEM) and a hybrid modelling are adopted for verification of the established model. It has been noticed that the 3D ETREE implements the fast and accurate computation of magnetic field signals of MFEC. Following that, the directional characteristics of EC with rectangular excitation coils are investigated, which reveals that the coil width contributes more to the measurement sensitivity than the coil length, and benefits the evaluation of defects and anisotropic conductivity profile of conductors in the follow-up study