Pulse-modulation eddy current screening of interlaminar defects in conductive heterostructures based on incident-field self-differential mechanism

Abstract Conductive heterostructures are broadly adopted in engineering fields involving energy, aerospace, etc., in virtue of their superior performance by integrating the favourable properties of different metals. However, due to hostile and particularly electrochemical environments, corrosion would occur within the body of the conductive heterostructure. Such interlaminar corrosion severely undermines the integrity and thus the performance of heterostructures. In light of this, it is imperative to non-intrusively detect and evaluate the interlaminar corrosion in conductive heterostructures via non-destructive evaluation methods before it progresses further. Following the proposition of pulse-modulation eddy current (PMEC) testing, in this paper the incident-field self-differential mechanism is intensively investigated, and exploited to achieve higher testing sensitivity to interlaminar corrosions. Based on the structure of the conventional pancake probe, an opposing excitation coil is introduced for cancelling out the localised incident field at the sensor position. A semi-analytical model is established for assessment regarding the PMEC response to a conductive heterostructure subject to the interlaminar corrosion. Closed-form solutions for prediction of testing signals are formulated and subsequently utilised for investigation of the probe performance. In a bid to further analyse the performance of the proposed probe, experiments are carried out, in comparison with the conventional pancake probe. The results from the theoretical simulations and experiments infer that in virtue of the incident-field self-differential mechanism the proposed PMEC probe is superior in high-sensitivity recognition of interlaminar corrosions in conductive heterostructures.