Residual Stress Determination for Cold Expanded Holes

ABSTRACT: Cold working has been used for holes in aircraft structure to extend fatigue life for decades. This procedure can be used as a terminating action or as an inspection interval extension. To have confidence in the process, the Air Force needs an inspection tool that can conclusively determine of the cold work process has been applied to a hole, and if the results are within process specifications. TRI/Austin has already developed a prototype tool, the FastenerCam, that performs this inspection on straight shank holes, using a contact fixture. In this effort, we will enhance the FastenerCam by making it non contact, and by developing the analysis software to assess countersunk holes. BENEFIT: The Air Force currently allows only a conservative approximation of the benefit of cold working fastener holes. The FastenerCam ensures that holes have been properly cold worked, allowing extension of inspection intervals, and often elimination of inspections for the life of structure. A review of the A-10 shows that 25% of the 120 inspection locations specified in Durability and Damage Tolerance Analysis involve cold worked holes. Eliminating only one inspection cycle for each of these locations would result in lower cost and increased availability, and this can be applied across all Air Force fleets.