ELEVATED TEMPERATURE FATIGUE CRACK GROWTH BEHAVIOR OF Ti-1100

Abstract— The fatigue crack growth behavior of Ti-1100 is analyzed at elevated temperatures to evaluate the effects of mechanical and environmental variables. Experiments conducted over a wide range of frequencies from 0.01 Hz to 200 Hz indicate a strong dependence of the growth rate upon cyclic loading frequency. Superposition of hold time at maximum and minimum loads over a baseline 1.0 Hz cyclic loading frequency produces an insignificant variation in crack growth rate, which may be attributed to the combined effects of enhanced environmental degradation, crack-tip blunting and increased asperity-induced closure level in this material. It is deduced that a hold time at maximum load results in an interaction of the environmental effects with a retardation effect due to crack tip blunting as a consequence of creep under maximum applied load, whereas for hold at minimum loads, extensive crack-branching and micro-cracking appear to enhance crack closure loads resulting in lower crack growth rates. A linear superposition model is employed to account for the complex interactions due to fatigue, creep and environmental degradation.