Finite element modeling of second layer crack detection in aircraft bolt holes with ferrous fasteners present

• Pulsed eddy current used to detect inner layer cracks in aircrafts with ferrous fasteners present.
• Finite element modeling used to simulate the probe and sample with cracks in bolt holes.
• Principal component analysis produced scores that successfully identifies the cracks.
• The method can also identify signals from an off‐centered probe.
• Modeling results are in good agreement with experiment.

Small cracks originating near bolt holes in the inner layers of aircraft lap joints cannot be detected by conventional eddy current techniques with ferrous fasteners present. The current work employs finite element modeling to investigate the effectiveness of pulsed eddy current (PEC) in detecting deep-lying cracks of different sizes and orientations. Differential signals analyzed using a modified Principal Components Analysis (PCA) method reveal the potential success of a PEC-PCA combination to produce scores that can be used to determine the presence of cracks. The method can also identify signals from an off-centered probe. Results are supported by experiment.