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Title: High-sensitivity eddy-current testing technology for defect detection in aerospace superalloys
Author: Hughes, Robert Rhys
ISNI:       0000 0004 5922 3241
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2015
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Industrial eddy-current testing (ECT) inspections of aerospace superalloys, such as Titanium 6Al-4V, must reliably detect sub-millimetre surface breaking defects. The sensitivity of such measurements is hindered by the materials' low conductivity and high coherent background material noise, making the high sensitivity standards required by industry harder to achieve. It is demonstrated herein that using eddy-current array (ECA) technology also introduces inspection "blind-spots", whereby small defects could be missed. This supports the motivation to develop techniques for enhancing the sensitivity of typical ECT and ECA measurements. The early stage research and development of a novel ECT measurement method is presented, and shown to improve the standard measurement sensitivity of industrial ECT inspections. A defect signal enhancement phenomenon within a band of frequencies close to the electrical resonance of an ECT probe, termed near electrical resonance signal enhancement (NERSE), was observed and characterised. This phenomenon was demonstrated to be a direct result of the shifting resonant frequency of the probe in the presence of material discontinuities. Frequency sweeping chirp signals were used to generate electrical resonance traversing frequency spectra measurements of the inspection probe in the presence of material discontinuities. Critical feature analysis of the results demonstrated a correlation between defect dimensions and peak NERSE amplitude, but failed to draw any conclusive trends between discontinuity dimensions and the resonant frequency shift. This was attributed to the relatively small defect sample set used and the size of many of the machined defects being smaller than the diameter of the inspection coil. An ECT probe was excited at a single frequency carefully selected to correspond to the NERSE peak frequency. A study was performed to statistically analysis the sensitivity of this NERSE measurement compared to a standard excitation frequency measurement used in industry. The results demonstrated that a NERSE frequency inspection was able to reliably detect a defect size of 0.82mm, compared to 1.09mm achieved by a standard operating frequency.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)