Cold expansion effects on cracked fastener holes under constant amplitude and spectrum loading in the 2024-T351 aluminum alloy

• One crack growth model is shown to be non conservative at high stress levels.
• Pre-cracked cold expanded hole life decreases exponentially with increased stress.
• Flaw size changes to account for cold expansion yields constant life improvement.

The increased number of aging aircraft in operation today requires a deeper understanding of fatigue life improvement methods. This research focused on the fatigue life benefit from cold expanded holes with preexisting cracks approximately 1.270 mm (0.050 in.) long under constant amplitude and wing spectrum loading. Holes with preexisting cracks were tested to simulate the worst case scenario of a hole with a crack the size of the detection threshold, 1.270 mm (0.050 in.), present before cold expansion that was not found by Non Destructive Inspection. Test results were compared to crack growth models generated in AFGROW. At high stress levels the AFGROW models yielded non conservative results greater than 150% of the test demonstrated fatigue life.