Investigation of pulsed eddy current probes for detection of defects in riveted structures

The fatigue crack is the threat to integrity and safety of fuselage lap-joints. Quantification of fatigue cracks by designing and utilisation of an optimised electromagnetic nondestructive evaluation probe can insure the flight safety of aircrafts. In this paper, pulsed eddy current (PEC) for detection and characterisation of fatigue cracks is investigated. The principle of PEC is analysed first, from which four different models of PEC probes are simulated in ANSYS. The signal features, namely zero-crossing time, zero-crossing frequency and peak value are extracted from the time and frequency domains in an effort to qualitatively compare the crack detectability of the four models. The sensitivities of the different probes to cracks are analysed quantitatively. The difference in detectability among the probes is investigated based on the working principle. Simulation results show that the probe consisting of two horizontal detecting coils along with a magnetic field shield focusing the flux has the highest detectability. The conclusions derived from the simulation study are also validated by experiments.