Inspection of Bonded Composite Structures Through Fairing Materials

The outer mold line of modern military aircraft needs to be as smooth as possible to achieve optimal aerodynamic and signature performance. This means that even minor imperfections in the fit-up of structural components at final assembly are often smoothed out with fairing materials prior to the application of any subsequent coatings.  Fairing materials are also often used at the time of structural repairs, such as for corrosion blend-outs on metallics or impact damage and other structural repairs of composites.  The inspection of these assemblies after the application of the final coating is difficult due to the unknown thickness of the fairing material and potential geometric steps that exist underneath. For ultrasonic inspections (which is the only practical inspection technique that can achieve USAF goals), this can result in unknown beam diffraction resulting in the loss of coverage or non-optimal beam alignment with respect to any hidden potential defects. To address this issue, Texas Research Institute (TRI) Austin will use simulation tools and experiments to determine how to estimate the structural shape that exists underneath coatings, modify beam shape to optimize reflection from defects, and implement pulse compression techniques for an improved signal to noise ratio. Techniques implemented in this work can be transitioned with our supporting partners NDTSolutions (NDTS) and Northrop Grumman Aeronautical Systems (NGAS).