Mechanism-Based Design Life Predictions in an alpha+beta and a near-alpha Titanium Alloy

The objective of this work was to develop and demonstrate a mechanism-based probabilistic life prediction method for the prediction of minimum fatigue lives in a component representative of an engine disk.  The fatigue life at a 1 in 1000 rate of low-cycle-fatigue cracking (or B0.1 life) is typically used in the design of fracture critical rotating turbine engine components.  In this work, a Monte Carlo analysis was applied to predict the variability in fatigue lives as well as the B0.1 life based on the distribution of microstructural features that lead to early crack initiation as well as the variability in small fatigue crack growth rates.  Testing conducted on two titanium alloys in both smooth and notched fatigue specimens was used for calibration and validation of the probabilistic predictions.  The predictions are presented and compared to the data for smooth and notch geometries for various loading conditions.  An analysis of a component geometry representative of an engine disk was conducted to demonstrate a comparison between the two alloys.  A parametric study was performed to identify the importance of several model inputs and to identify areas for future model improvement.