Airframe Metal Fatigue Revisited

Abstract Good fatigue design and prognostics are essential for safe and sustainable aircraft. A common feature in all metallic fatigue failures is the presence of structural cracks that propagate during the life of the structure. There are fatigue crack growth prediction tools (and certification processes) that have largely ensured flight safety by utilizing crack growth rate data generated from physically large cracks. However, unexpected fatigue cracking and non-critical failures still occur, which increases the cost of aircraft sustainment. This paper attempts to define some of the reasons why these sustainment-related cracking problems can occur and some means of redress. The discussions are limited to production quality metals and fabrication processes.