Characteristics of Eddy Current Attenuation in Double-Layer Metallic Plate and Measurement of Gap Thickness

Abstract

ABSTRACT Multilayer metallic plate is made by stacking homogeneous or heterogeneous metallic plates and connecting them with fasteners. The air-gap thickness between the adjacent layers affects the performance of the plate structure. The eddy current testing (ECT) technology has been used for the nondestructive testing of multilayer plate. However, the effect of air gap on the characteristics of eddy current (EC) attenuation in multilayer plate remains unclear and the study of the relation between the response of the EC probe and the gap thickness is very limited. The computation results of the paper show that the air gap in a double-layer plate reduces the amplitude of EC density in the bottom layer and decreases the rate of EC attenuation in the top layer. The mechanism is revealed. The effect of gap thickness on probe response is investigated. It is found that the presence of air gap makes the EC response either larger or smaller, depending on the working frequency. The reason is explained based on the characteristics of EC attenuation. Thereupon, the experiment of measuring gap thickness using the ECT is carried out.