Staircase testing of a titanium alloy in the gigacycle regime

The objective of this research was to investigate the high cycle fatigue behavior of a titanium alloy using an ultrasonic fatigue system. Fatigue testing from 106 to 109 cycles under fully reversed cycling (R = −1) was performed to determine the ultra-high cycle fatigue behavior of Ti–6Al–4V. The staircase test method was employed to obtain accurate values of the mean fatigue limit stress corresponding to fixed numbers of cycles up to 109. These results were compared to similar data generated on conventional servohydraulic test systems and electromagnetic shaker systems to determine if there are any frequency effects. In addition, specimens were tested with and without cooling air to determine the effects of temperature on the fatigue behavior. Results indicate that the fatigue strength determined from ultrasonic testing was consistent with conventional testing. In addition, the temperature rise in this material during ultrasonic testing is insignificant and has no apparent effect on the endurance limit.