Improved Nut Plate Fastener Hole Eddy Current Probe

To address the Air Force"s need to perform a quantifiable inspection of the inside region of fastener holes with installed nut plates, UniWest proposes to design a probe that optimizes pertinent parameters to position the sensing mechanism at the edge of the fastener hole (including surface area right under the nut plate). The parameters include (but are limited to): probe geometry design, coil design, shielding, coil placement, inspection technique, and material. A Probabilty of Detection (PoD) test will be demonstrated utilizing Air Force inventory instrumentation and scanning mechanisms. Phase I will address the feasibility of a probe design which accurately inspects fastener holes with installed nut plates for flaws, including surface area right under the nut plates, and no damage to probe or aircraft. A PoD plan In Accordance With (IAW) HDBK-1823A will be presented. Phase II will refine probe design based on feedback, and PoD demonstration will be performed to compare the detection capability of current and the new probe designs for cracks emanating at the surface where the nut plate is attached. Phase III will perform dual use commercialization, applying the probe to all military aircraft, as well as all commercial aircraft, that utilize nut plates. BENEFIT: Improved flat-bottom bolt-hole probe designs increase the reliability of flaw detection at the interfaces between fastener holes and nut-plates, thus reducing the risk of material failure originating from a known stress-riser. This would allow a reduction in inspection frequencies, lowering aircraft ownership costs and significantly improving aircraft safety in the military as well as commercial sectors.