| Fully reversed bending fatigue tests conducted on specimens of aluminum alloy 2024-T351 in dry and humid air at stress levels of 36, 42, 48 and 52 ksi showed that humid air reduces the fatigue life by as much as 21%. The reduction in fatigue life was primarily attributed to localized hydrogen induced overaging. The fatigue life in humid air was found to be exposure time dependent with the greatest detrimental effect observed at 36 ksi. Dry and humid air specimens cycled at 52 ksi showed parallel fatigue lives and a scanning electron microscope analysis of the fracture surfaces also indicated similarities. Data from this research and from past studies on the 2XXX series aluminum alloys were combined to offer a plausible mechanism for environmentally induced fatigue in aluminum alloy 2024-T351 at any stress level. |
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