Fatigue crack growth testing using varying R-ratios

A method to generate high temperature fatigue crack growth data for multiple R-ratios during a single or only a few tests for surface crack specimens was developed. Two tests were performed; one with 0≤R≤0.8 and one with −1≤R≤0. The crack growth was monitored using the potential drop method. It was shown that the results from tests with varying R-ratio gave very similar results to test with constant R. Fatigue crack growth predictions with data from varying R-test were generally slightly more conservative compared to predictions using data obtained from conventional testing.