Fatigue Crack Growth of Two Advanced Titanium Alloys at Room and Elevated Temperature

Abstract

This paper provides fatigue crack growth information at low crack growth rates for two sheet titanium alloys: β-21S, a β alloy, and Ti-62222, an α + β alloy. Room (25°C) and elevated temperature (175°C) fatigue crack growth tests at two different stress ratios, R = 0.1 and 0.5, were performed. Effects of temperature and stress ratio were evaluated in order to study the complex interaction between fatigue, environment, and loading conditions. Crack-opening load was measured throughout the test from automated compliance measurements and was used to adjust fatigue crack growth data for crack closure. For β-21S, fatigue crack growth rates were similar at 175 and 25°C at a stress ratio of 0.1, while crack growth rates were lower at 175 versus 25°C at a stress ratio of 0.5 for the same nominal ΔK. Concepts associated with crack closure accounted for this as crack growth rates were found to be higher at 175°C than 25°C for both stress ratios when plotted as a function of ΔKeff, showing a temperature dependency on crack growth rate. For Ti-62222, fatigue crack growth rates were comparable between 25 and 175°C for R = 0.5, but were different at R = 0.1 where crack closure was observed at 175°C. Fatigue crack growth behavior of these two titanium alloys was comparable for all loading and temperature conditions.