Abstract
An investigation of the effects of stress ratio and temperature on the near-threshold fatigue crack growth characteristics of Ti-8Al-1Mo-1V was performed. Computer-controlled decreasing stress intensity range tests using compact tension specimens were conducted for various stress ratios at temperatures of 76°F (24°C) and 500°F (260°C) in laboratory air. Crack opening load was determined throughout the tests based on automated compliance measurements and was used to adjust the fatigue crack growth rate data to effective stress intensity range ( ΔK eff ). The effects of stress ratio at a constant temperature were able to be explained by the concept of crack closure and ΔK eff . However, crack closure was not able to account for the effects of temperature at a fixed stress ratio of 0.1, as higher near-threshold crack growth rates were observed at 500°F (260°C) when the data were plotted as a function of ΔK eff . This difference in crack growth rate is believed to be attributable to significant crack front branching and secondary cracking as a result of the increased oxidation at 500°F (260°C). A unique value of fatigue crack growth rate threshold, ΔK th was observed for all of the test conditions when crack closure was accounted for in the data analysis.
Published Version
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