Abstract
In the search for ever more sensitive non-destructive testing (NDT) techniques to detect progressively smaller defects in increasingly complex industrial materials, environments and geometries, conventional eddy-current testing (ECT) methods, have reached their sensitivity limit. Fortunately, advanced resonance-based techniques, demonstrated in recent years, promise to help extend that limit, but, before such techniques can be implemented with confidence, a detailed understanding of their sensitivity and stability must be achieved. In this study, statistical probability-of-detection (PoD) analysis was performed to assess the sensitivity of a novel single-frequency, near electrical resonance signal enhancement (SF-NERSE) technique relative to an equivalent conventional probe operation. This study was performed on 36 real fatigue defects in Titanium 6V-4Al (Ti6-4) with defects ranging from 0.10−6.48 mm in surface extent. In addition, a critical evaluation of background noise stability in the SF-NERSE technique (a common concern with NERSE-based methods) was also performed to establish the viability of such a technique in relation to industrial inspection and assessment criteria. The results of this study demonstrate a sensitivity enhancement of up to 20% for the SF-NERSE method over conventional operation and, through controls, confirmed that the effect is a result of the resonance-shifting phenomenon and not just an increase in operational frequency. In addition, an examination of background noise implies that a SF-NERSE method exhibits more stable background noise than conventional excitation. This study validates the SF-NERSE technique and methodology as a viable industrial inspection technique, able to significantly improve detection capabilities.
Highlights
The structural integrity of industrial components is paramount for ensuring safety
To inform the definition of athresh in PoD analysis, a study was performed on the three different excitation approaches, using three different methods to analyse background noise
The results demonstrate that operating at fNERSE for a given sensor can reliably enhance the sensitivity to defects by 13 − 20%, relative to conventional inspection frequencies, and depending on the definition of athresh
Summary
There is no better example of this than in modern air travel, where the failure to detect component damage can have a catastrophic economic and human cost [1] This was demonstrated by the recent Southwest Airlines engine failure, reportedly caused by undetected metal fatigue, resulting in the loss of a fan blade mid-flight, and the subsequent fatality of a passenger [2]. ECT is one of the most sensitive inspection techniques for detecting surface defects, capable of detecting sub-mm defects in ideal conditions In recent years these inspections have approached a fundamental limit in their sensitivity, based on the size of manufacturable sensors. The arbitrary maximum approach used in this study is more representative of the potential for false calls within an industrial inspection The result of these processes is a phase invariant measurement of defect signal and background noise. In order to accurately assess the PoD of a given technique, suitable decision thresholds must be established
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