EFFECTS OF SHORT‐TERM HEATING CYCLES ON FATIGUE CRACK GROWTH IN 7075‐T651

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Abstract
Changes in the crack growth behavior of 7075‐T651 aluminum specimens which had been exposed to temperatures between 121 and 179°C were evaluated. Specimens were fatigue tested at room temperature under flight‐by‐flight loading conditions. Results from these tests were then compared with data from the as‐received material. Exposure to 141°C or more produced a definite increase in specimen life, apparently due to a decrease in crack growth rate. In contrast, preliminary experiments using constant amplitude loading did not show noticeable effects of these thermal treatments on fatigue lifetime. The thermal treatments were found to cause overaging of the metastable precipitate microstructure, which was thought to be responsible for the changes in fatigue response.