Cold Expansion Effects on Cracked Fastener Holes Under Constant Amplitude and Spectrum Loading in the 2024-T351 Aluminum Alloy.

摘要

Current United States Air Force maintenance techniques require that any discontinuity (crack, pit, gouge, or other defect) detected in a hole be removed by oversizing the hole or replacing the part. What if cold expansion could be proved to extend the life of a cracked component well beyond the time to the next required inspection? This research investigates the effects of cold expansion on cracked holes. This research compares the fatigue lives of clean (no detected discontinuities) cold-expanded holes with the fatigue lives of holes cold-expanded after a 0.050 inch fatigue crack had nucleated. The experiments conducted herein investigate various stress levels under constant amplitude and spectrum loading conditions. The percent cold expansion is calculated for each specimen, and the amount of crack growth from cold expansion was measured. Finally, this work compares the tested fatigue lives with analytical predictions using Lextech Inc. AFGROW software utilizing an assumed 0.005 inch initial crack size to account for the benefit of cold expansion, consistent with most industrial aerospace damage tolerance analysis.