Dwell-fatigue life dispersion of a near alpha titanium alloy

An experimental study was undertaken to examine the evolution of life, strain, strength and damage in titanium IMI 834 during dwell-fatigue loading conditions. The tests were conducted on smooth cylindrical specimens under load control with trapezoid wave form of 0.033 Hz frequency and zero load ratios. The specimens were cut from identical disk forgings and tested in the same conditions at room temperature, as it is normally done in the industry. Thirty seconds dwell time was imposed at the maximum load test, 824 MPa (90% of the yield strength). The total rigidity decrease during the test was plotted against the number of cycles for all specimens. Jumps were observed in the curves. They may be related to the nucleation and propagation of cracks in the material. Scanning electron microscopy observations show that all failures take place from a sub-surface nucleation site which seems to nucleate at random times during the dwell-fatigue tests.