The present investigation utilized previously developed and reported statistical methods to study the effects of variation in microstructure (extruded and extruded plus recrystallized) on the fatigue properties of 24S-T4 aluminum-alloy notched specimens tested in both the longitudinal and transverse directions.nThe results show that a definite anisotropy exists in the fatigue strength of this alloy in these tests. This anisotropy is found only for the material in the extruded condition} the extruded and recrystallized material shows no significant anisotropy and essentially the same fatigue properties as the extruded material in the transverse direction. Corre-lation tests with unnotched extruded longitudinal specimens shoved that there is more scatter in unnotched than in notched specimens; within the range of stresses tested (and of resulting life), the fatigue-strength reduction factor Kf increases with increasing stress. The effect of microstructure on the resulting fractures was also investigated.
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