A study has been conducted on the initiation and growth of fatigue cracks in the three principal directions of an aluminum alloy 2024T351 plate tested under stress control (R, minimum to maximum stress= - 1). Early and multiple fatigue crack nucleation from broken Al,Cu,Fe second phase particles resulted in shorter lives for the longitudinal direction specimens in the medium to long life regime. Although fatigue cracks nucleated in large surface grains, rather than at broken particles, the lives of the short-transverse direction specimens were marginally longer. Cracks also nucleated in large surface grains in the transverse direction specimens, yet the average fatigue lives were about twice as long. This was the consequence of wider slip bands and fewer initial micro-cracks.

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