ABSTRACT
Fatigue crack growth continues to be a challenge in aerospace structures, requiring significant effort in terms of prediction of fatigue life, and the use of substantial safety factors to ensure that the risk of failure remains low. While many modern designs rely on prediction of fatigue crack growth rate such that cracks may be detected and managed during service, there are many components, notably high-strength components such as undercarriages and helicopter parts, which rely on design to a Safe Life. This approach relies on a scatter factor on service life to avoid crack development in all but a very small part of the population. Safe-life design utilizes Stress-Life (or S-N) curves, which are graphical representations of the fatigue life of a material under different loading conditions. These curves are usually created for constant amplitude loading, and allows synthesis of a total life estimate by assessing the damage accumulated at each of several constant amplitude load levels.
