Abstract
Inclined fatigue cracks can potentially cause severe damage to metallic structures as they affect larger region in the tested structure compared to crack perpendicular to the sample surface. The abilitiy to detect and characterize such cracks is paramount in non-destructive testing (NDT). Pulsed eddy current testing (PEC) is known to offer a broadband of excitation frequencies, which in conjuction with C-scan imaging, may offer discrimination of inclination angles of cracks. Finite element modelling (FEM) was carried out to study the effects of different crack inclination angles, while experimental results were used to verify the FEM results. Selection of both time and frequency domain features for C-scan image construction was also presented, where C-scan images of peak value and amplitude at 200 Hz were shown to be potentially capable in determining different inclination angles. Nevertheless, between these two signal teatures, the amplitude at 200 Hz was found to be more effective in the discriminataion of inclined cracks.
Highlights
Belonging to the electromagnetic non-destructive testing (NDT) category, pulsed eddy current testing (PEC) is renowned for its beneficial wideband excitation of magnetic field into a tested metallic structure [1]
Response signal is the resultant magnetic field when the induced eddy current is perturbed by the presence of flaws while differential signal is the subtraction of reference signal from the response signal [3]
The features tend to reach their maximum or minimum values away from the middle of the crack opening. This observation was verified with finite element modelling (FEM), which was built according to the parameters of the PEC system
Summary
Belonging to the electromagnetic non-destructive testing (NDT) category, pulsed eddy current testing (PEC) is renowned for its beneficial wideband excitation of magnetic field into a tested metallic structure [1]. This induces transient eddy currents into the structure, which in turn, induces a secondary magnetic field opposing the primary magnetic field. Reference signal refers to a resultant magnetic field picked up by the sensing element when no flaws are present. Response signal is the resultant magnetic field when the induced eddy current is perturbed by the presence of flaws while differential signal is the subtraction of reference signal from the response signal [3]. A differential signal basically contains the information due to the change in the induced eddy currents
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