Predicting Fatigue Life Under Spectrum Loading in 2024-T3 Aluminum Using a Measured Initial Flaw Size Distribution

Abstract

Abstract Measured cracked particle distributions were used in conjunction with a closure-based life prediction package (FASTRAN 3.8 [1]) to predict fatigue life distributions under a spectrum load (FALSTAFF — Fighter Aircraft Loading STAndard For Fatigue [2]) in 2024-T3 aluminum. A single crack model was assumed and no threshold stress intensity factor was used. Simulations were done at maximum stress levels of 175, 205, and 275 MPa. The resulting fatigue life distributions were compared at different levels of probability of failure. At all levels, predicted fatigue lives were within a factor of two or better of experimental fatigue lives. This indicates both that the single-flaw model can be a reasonable approximation for life prediction and that it is not necessary to truncate initial flaw size distributions at some threshold level.