Abstract : Many fatigue-related studies have been conducted on the workhorse alloys for airframe construction over the past 20-30 years. The body of empirical knowledge related to establishing relationships between loading conditions and fatigue life or fatigue crack growth rates, including environmental effects is vast. One consistent observation is that the number of cycles it takes to initiate a fatigue crack (imitation life) in high strength aluminum alloys, like AA 7075, is a significant fraction of total life. Fundamental understanding of what causes fatigue cracks to initiate is elusive, however, and current alloy and airframe component design methodologies remain highly empirical processes.