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Title: Eddy current array optimisation
Author: Egbeyemi, Abbas Akinola Akanni
ISNI:       0000 0004 8497 6034
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2018
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There is a drive in industry to reliably detect surface breaking sub-millimetre defects in low electrical conductivity materials, such as stainless steel, titanium, and titanium aluminide using eddy-current testing. The sensitivity of the eddy current method to these materials is hindered in part by their low conductivities, and complex grain structures, which makes the high sensitivity standards required by industry more difficult to achieve. Eddy current measurements for sub-millimetre defects in low conductivity materials are routinely performed using a high excitation frequency, to decrease the skin depth of induced eddy currents into the material, which would otherwise be higher due to the reciprocal relationship between depth of penetration, and material conductivity. The fundamental components of an eddy current array is a pair of coils, and thus finite element models are presented in this thesis, and are used to investigate the interaction between low conductivity materials, and a pair of eddy current coils operating in absolute, and transmit-receive modes. The model results give insight to the eddy current coil voltage response to defects, and the relationship between absolute mode, and transmit-receive mode data when taken concurrently. Experiments are performed, which show how the combination of a voltage amplitude C-scan image with its corresponding voltage phase C-scan image, results in an image with a significantly improved signal to noise ratio. In the same experiments, absolute mode data is also combined with transmit-receive mode data to generate a single image with signal to noise ratio values significantly higher than anything achievable using individual images. Varying levels of noise are added to the data to investigate the limits at which this data processing method can be utilised. Low conductivity materials such as titanium aluminide, containing defects as small as 0.25 mm were scanned, and promising results were achieved showing that defects this small can be reliably detected using the inspection method, and data processing techniques presented in this thesis.
Supervisor: Not available Sponsor: Ether NDE Limited
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General) ; TK Electrical engineering. Electronics Nuclear engineering