High cycle and very high cycle fatigue of TC17 titanium alloy: Stress ratio effect and fatigue strength modeling

The fracture surface of TC17 alloy tends to exhibit facet characteristic at R > 0, but it presents rough area morphology at R = -1 for the internal crack initiation and early growth region. The former is attributed to basal slip or cleavage of alpha grains. The later is due to the cracks caused by the nanograin formation and the cracks formed irrespective of nanograins. The present TC17 alloy and various alloys in literature indicate that Walker's equation [(1-R)/2](alpha) is more accurate than Goodman's equation and Smith-Watson-Topper's equation [(1-R)/2](1/2) for the effect of stress ratio on high cycle and very high cycle fatigue strength.