Aircraft Embedded Fastened-Joint Assessment Sensing Tool (FAST)

Aircraft structural elements are usually assembled using single-sided fasteners. That is to say, pins with flush heads on one end and threads on the opposite end to be joined with collars designed for specific torque levels. Examples of these types of aerospace fasteners include Hi-Lok, Hi-Lite, Hi-Torque, and TAPER-LOK. Unfortunately, fastened joints also provide unique opportunities for hidden damage, including fatigue cracks, corrosion and fretting. This is due to the local stress concentrations of the hole, friction between fastener and surrounding material, and the fact that moisture can ingress and be trapped between the fastener and layers being fastened. The complex multi-layered geometry at these joints also makes it challenging for conventional inspection techniques without disassembly. This proposal addresses this problem with a distributed network of sensors that integrate with the fasteners themselves to provide local hidden damage detection capabilities. Through prior Navy SBIR efforts this impedance-based approach has shown success in Hi-Lok and Hi-Lite fasteners for rotorcraft, thus this effort will aim to customize the sensors and algorithms for USAF-relevant Hi-Torque and TAPER-LOK fasteners that do not have standard hex-recesses. A Phase II program will consist of a detection sensitivity study, an airworthiness assessment and a flight test demonstration.