Cryocooled SQUID Magnetometer Array for Laboratory Measurements of the Rate of Hidden Corrosion in Aging Aircraft

There are no established techniques for determining instantaneous rates of hidden corrosion in aluminum aerospace structures, such as crevice corrosion in an aircraft lap joint or exfoliation corrosion in the midplane of a thick wing plank. Studies showthat SQUIDs are ideally suited for non-destructive analysis of corrosion in specimens where the corrosion activity is not directly accessible to more conventional electrochemical analyses. We will develop a new laboratory technique that incorporates aSQUID magnetometer that will be suitable for quantifying the rate at which various forms of corrosion damage accumulate in a range of aerospace structures. Our design incorporates important technical innovations, including the use of a 2-dimensional arrayof SQUID sensors for rapid scanning and spatio-temporal correlation, improved scanning technology, and advanced analysis software. We will develop the instrument in two stages besinning with a 2-channel prototype to verify sensor performance and cryogenicrequirements. We will then fabricate a 16 channel SQUID magnetometer system and place it in a compact magnetic shield and scanning stage system. Based on the metrics developed in the Phase I effort (allowing quantitative comparison of our proposedtechnique with existing techinques) we will measure exposed and hidden corrosion specimens to demonstrate the system's capabilities.