ELEVATED-TEMPERATURE FATIGUE BEHAVIOR OF SCS-6/TI-24AL-11NB

An investigation has been conducted to determine the effects of stress ratio, frequency and hold time on the elevated temperature fatigue behavior of SCS-6/Ti-24Al-11Nb. Load-controlled tests conducted at 650-degrees-C, and two stress ratios, 0.1 and 0.5, are compared at a frequency of 3 Hz. The baseline tests at 3 Hz are compared with data at three other frequencies: 30, 0.0083 and 0.00278 Hz. The effects of superimposed hold times were also investigated at the lowest frequency, 0.00278 Hz. Cycles to failure are compared for all the data sets, and life-fraction models were developed which take into account both the time-dependent and cyclic-dependent effects of this composite material. The model is capable of predicting cycles to failure for the frequency range investigated and is based on data resulting from the highest frequency fatigue as well as creep testing. This linear life fraction model is extended successfully to account for hold times.