Luna Innovations Incorporated proposes in this STTR Phase II project to continue development and validation of Luna's amplitude-dependent, nonlinear ultrasonic inspection technique applied to friction stir welded (FSW) components. The technique was successfully demonstrated in the Phase I project on samples made from aluminum-lithium alloy 2195. The proposed Phase II project will focus on refining the ultrasonic hardware and software needed to implement the technique on materials and weld geometries with near-term application in support of the Constellation launch vehicle development program. A multi-channel sensor implementation is planned. Luna's results will be compared to conventional NDE techniques currently used; this testing will be conducted primarily by collaborators at the University of Alabama, Huntsville (UAH). The project will also include a review of state-of-the-art NDE techniques applied to FSW joints and early planning for comprehensive probability of detection experiments needed to fully qualify the new technique.