It is proposed to develop novel eddy current probes based on spin dependent tunneling (SDT) magnetoresistive (MR) sensors to enhance the probability of detection of cracks within the bore of installed Taper Lok fasteners. Preliminary results show that the use of shaped excitation coils, together with extremely sensitive SDT sensors properly positioned above the structure under inspection, provides a significant improvement for deep crack detection around fasteners. By using specific coil geometry, the eddy current density can be focused on the circular edge of the fastener hole, where cracks can initiate. Consequently, the perturbation of the eddy current flow due to the presence of the crack is greatly enhanced. The proposed rotating self-nulling probe does not require either additional ferromagnetic flux focusing lenses, or compensation of the excitation field, as in prior art. Within this phase I project, different coil geometries and location of the sensor relative to this coil will be compared and the performance limitations of each design will be studied. A simple manual scanning system will also be developed for fast inspection of holes.
Benefits: The novel eddy current probes will provide an effective tool for detecting small cracks within thick wing splice joint structures, without the need to remove the Taper Lok fastener. It is envisaged that the proposed approach will outperform current state-of-the-art eddy current techniques used to address this difficult problem, in terms of both size and depth of defects that can be reliably detected around the fastener holes. Both military and commercial aircraft industries will directly benefit from the development of these novel probes.
Keywords: Non-destructive evaluation, Eddy current testing, Giant magnetoresistive sensors, Crack detection, Aging aircraft, Spin dependent tunneling, Wing-splice structure
