Non-Destructive inspection (NDI) of Cracks, Corrosion, Etc. in second and third Layer materials around Fastener Holes

One objective is to demonstrate the use and value of SQUID Magnetometry for locating fatigue cracks around fastener holes in multiple layered structures without disassembling the structure or removing the fasteners, in instances where the crack lies in an under layer of the structure and is therefore not directly accessible from the structure's outer surface. A second objective is to demonstrate the application of existing digital signal processing and data enhancement techniues, which have previously been applied to data outputs from various surveillance sensors, to data outputs from a point inspection Nondestructive Inspection sensor. The program involves making SQUID Magnetometry measurements from 3 samples of flawed structures relating to the C-141 aircraft wing, and processing this data into signal patterns from which cracks of prior known location and length can be identified and measured. Success will demonstrate the utility of SQUID Magnetometry in finding hidden fatigue cracks. An NDI method with this capability will prove useful both to the Air Force for inspecting its aging aircraft, and to commercial aviation which must inspect many of the same airframes used by the Air Force.