Notch fatigue behavior of Ti-6Al-4V alloy in transition region between low and high cycle fatigue

The load-controlled and displacement-controlled fatigue tests of Ti-6Al-4V alloy notched specimen under the remote stress ratio of 0.1 were carried out in order to investigate notch fatigue behavior in a wide range of fatigue life from low to high cycle fatigue. The elastic-plastic finite element analysis of notched specimen under cyclic loading was also conducted to investigate the variation of local stress ratio at notch root and its influence on fatigue life. It was found that the local stress ratio at notch root varies from the remote stress ratio of 0.1 in high cycle region to −1 in low cycle region, where the transition region is defined as the region of local stress ratio variation. Taking account of the local stress ratio variation at notch root, fatigue life was predicted based on the SWT parameter combined with the FEA was in good agreement with the experimental results. It is suggested based on these local stress variation and fatigue life prediction that the low cycle fatigue life predicted assuming the stress ratio of −1 would give an unsafe side prediction in the transition region.