Investigation of cold expansion of short edge margin holes with preexisting cracks in 2024-T351 aluminum alloy

When a crack indication is found at a hole, current United States Air Force (USAF) technical data require that the hole must be oversized to a larger diameter to remove the damage. Unnecessarily oversizing a hole is undesirable from a fatigue point of view. This research has the potential benefit of not requiring the hole to be oversized and potentially could reduce the number of inspections required for aircraft. The experiments performed in this research investigated the fatigue crack growth lives of short edge margin holes. Three configurations were used â€" a baseline condition consisting of non-cold-expanded holes, another baseline condition of holes that were cold-expanded, and the test condition of holes containing a crack when cold-expanded. All configurations were loaded under constant and variable-amplitude loading. The hypothesis is that the cold expansion of a hole with a preexisting crack will provide a significant increase in fatigue life compared to an identical hole that was not cold-expanded. Additionally, the USAF analytical approach used to account for the fatigue life benefit due to cold expansion is compared to the experiment data, and may not be providing conservative predictions for the specific geometry and loading used in this experiment.