Variation of local stress ratio and its effect on notch fatigue behavior of 2024-T4 aluminum alloy

• S–N curve of the notched specimen was kinked at certain nominal stress amplitude.
• Local stress ratio at the notch root decreased with increasing stress amplitude.
• Fatigue life prediction improved by considering variation of local stress ratio.

Fatigue tests and finite element analysis of notched specimen were carried out to investigate the variation of local stress ratio at notch root and its influence on fatigue strength. The S–N curve of 2024-T4 aluminum alloy was kinked at the critical nominal stress amplitude, above which the local stress ratio became low due to the development of local plastic deformation at notch root. The predicted fatigue lives based on linear fracture mechanics approach were in agreement with the experimental results below the critical nominal stress amplitude. The predicted fatigue lives based on the SWT parameter, where the variation of local stress ratio was taken into account, were in good agreement with the experimental results above the critical nominal stress amplitude.