Developing the Capability to Monitor Small Fatigue Crack Growth Under Elevated Temperature, Ultra-High Vacuum Conditions (Preprint)

摘要

It has been observed that the life limiting fatigue behavior in numerous superalloys is dominated by small crack growth behavior. While environmental effects on crack growth behavior of Ni-base superalloys are well documented within the literature, the published research is largely limited to long crack behavior due to the difficulty of measuring small cracks in a vacuum chamber. A testing capability for optical measurement of small cracks under ultra-high vacuum and at elevated temperatures has been developed. Optical measurement capabilities have been evaluated on a lab air machine to determine crack measurement accuracy. Vacuum tests were then run at 650 deg C on Ni-base specimens to quantify the effect of vacuum on the propagation life within the small crack regime. The effectiveness of this test capability and considerations for this technique are discussed.