An investigation of short and long fatigue crack growth behavior of Ti–6Al–4V

This paper presents the results of a study of the effects of positive stress ratios on the propagation of long and short fatigue cracks in mill annealed Ti–6Al–4V. Differences between the long fatigue crack growth rates at positive stress ratios (R=Kmin/Kmax=0.02–0.8) are attributed largely to the effects of crack closure. Microstructurally short fatigue cracks are shown to grow at stress intensity factor ranges below the long crack fatigue threshold. Anomalously high fatigue crack growth rates and crack retardation are also shown to occur in the short crack regime. Differences between the long and the short crack behavior at low stress ratios are attributed to lower levels of crack closure in the short crack regime.