Residual Stress Determination for Cold Expanded Holes

For decades, cold working has been used to extend the fatigue life of aircraft fastener holes. This procedure may be a terminating action or used to extend the inspection interval/lifetime.To have confidence in the process, the Air Force (AF) needs an inspection tool to conclusively determine: 1.) that cold working has been applied to a hole and 2.) if the results are within specifications. TRI/Austin has developed a prototype tool, the FastenerCam, to perform non-contacting inspections of aircraft surfaces. In addition to examining the fastener geometry, including the diameter, countersink angle, depth, and alignment, FastenerCam measures and correlates the vertical deformation around the hole to the degree of expansion. During Phase I, its capabilities were extended to include countersunk holes and the system was redesigned to perform non-contacting measurements, permitting work in tight spaces without damaging coatings around holes being inspected.During Phase II, TRI/Austin will expand FastenerCams use cases to holes cold expanded through multiple plate layers, asymmetrically expanded holes, and countersunk holes expanded using Fatigue Technology Inc. (FTIs) countersink specific toolset.Finally, TRI/Austin will develop a manufacturing prototype to permit this technology to be immediately brought to market upon completion of Phase II.