The effect of sheet thickness on fatigue crack retardation in 2024-T3 aluminum alloy

Variable-amplitude fatigue studies of 2024-T3 aluminum alloy were performed to examine the effect of sheet thickness on fatigue crack growth rate retardation. Results indicated that the amount of retardation increased with decreasing specimen thickness. This phenomenon was attributed to enhanced plastic strains under plane stress conditions (i.e. in a thin sheet) which formed ahead of the advancing crack tip as a result of a high load excursion. These strains are believed to produce both crack closure and a favorable compressive residual stress field around the crack tip. Evidence of increased crack surface interference under plane stress situations was verified with electron fractographic observations.