A study of nucleation and fatigue behavior of an aerospace aluminum alloy 2024-T3

The fatigue failure process exploits the weakest links (discontinuities) within the test material, which act as nucleation sites for crack origins. This paper summarizes the results of a study on the 2024-T3 aluminum alloys in different forms (clad and unclad), loading directions, thickness and environment. Microstructural features such as particles, grain size, and clad layer, which dominate fatigue performance have been identified, classified, and statistically characterized. Two distinct mechanisms were found to be responsible for crack nucleation. Constituent particles were found to be the crack origins in unclad sheets. There was almost no evidence of multiple nucleation sites in the unclad material. The fatigue crack origins in clad sheets, however, were located at the surface of the clad. No constituent particles were found to be associated with crack nucleation. Multi-nucleation sites were observed in the clad material.