Effects of Variations in Coldworking Repair Procedures on Flaw Growth and Structural Life

J. M. Pearson-Smith

01/1984 · Flight Dynamics Laboratory, Air Force Wright Aeronautical Laboratories, Air Force Systems Command, United States Air Force

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Out-of-tolerance cold hole expansion can occur during scheduled maintenance of aircraft structures. Personnel responsible for the maintenance of aircraft structures must make decisions as to the acceptability of any deviation from repair specifications. The decision to accept or reject an out-of-tolerance repair can be significant in a scheduled maintenance situation since a rejection will normally involve a major integral component of structure. A rejection of a discrepant hole at the repair stage can mean scrapping of the component with the potential of thousands of person-hours for replacement and refurbishment. The purpose of this research effort was to investigate the effect of out-of- tolerance cold hole expansion on flaw growth and structural life. To accomplish this goal, specimens were prepared and fatigue tested under spectrum loading conditions to failure. Typical discrepancies found in structures undergoing repair were simulated for this effort. Crack length measurements were periodically obtained during the spectrum test and the resultant fatigue lives were noted. Crack growth behavior and fatigue lives for the holes with discrepant preparation were compared to those of properly prepared specimens.