Defect classification in two-layer complex structures based on spectrum analysis of pulsed eddy current

Abstract

Pulsed eddy current (PEC) testing is an increasingly emerging non-destructive testing and evaluation (NDT&E) technique. Defect classification is one of the most important steps in PEC defect characterisation. It is difficult to classify defects in two-layer complex structures of ageing aircraft or other complex structures. As a result of taking a square-wave signal as excitation, the PEC response signals contain rich information in the frequency domain. In this paper, two defect classification methods based on spectrum analysis are proposed to classify the defects in two-layer complex structures. Method 1 is based on direct frequency spectrum analysis, while method 2 is by means of differential frequency spectrum analysis. Experimental tests and blind tests are carried out and the results show that the different classes of defect can be identified and classified effectively. The lift-off test results show that the lift-off effect can be restrained by the proposed method. The frequency spectrum method has a good prospect in the field of PEC non-destructive testing and evaluation.