Pulsed eddy current technique used for non-destructive inspection of ageing aircraft

It is difficult detecting flaws in multi-layered structures such as aircraft fuselage lap splices. Pulsed eddy current (PEC) is an effective method that has been demonstrated to be capable of quantifying such defects. Different from conventional eddy current testing techniques, the exciting coil of PEC is fed by a pulsed waveform, the transient response signal in time domain is analysed, peak amplitude and zero-crossing times are extracted to detect and characterise flaws. PEC is used to quantify cracks found in aircraft structure, with the purpose of overcoming the problem of low accuracy of PEC in the classification of defects. A new feature, namely the frequency spectrum separating point, is proposed for defect classification. Finally, an array PEC imaging method is proposed to detect corrosion appearing in the second layer of aircraft structure.