Thermal mechanical fatigue crack growth in titanium alloys: Experiments and modelling
- Ecole Polytechnique, Montreal, Quebec (Canada). Dept. of Materials Engineering
- Pratt and Whitney Canada, Longueuil, Quebec (Canada)
Strain controlled thermal-mechanical fatigue crack growth (TMFCG) tests were conducted on two titanium alloys, namely Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo, to evaluate the effect of phase angle between strain and temperature on the TMFCG rates. Three fracture mechanics parameters were used to correlate the data: The {Delta}K, {Delta}K{sub {epsilon}} and {Delta}K{sub eff}. A fractographic study of the specimens tested under TMF was carried-out to identify the mechanisms responsible for cracking in these two titanium alloys. Hence, specimens tested under in-phase ({epsilon}{sub max} at T{sub max}), out-of-phase ({epsilon}{sub min} at T{sub max}) and counter-clockwise diamond (90{degree} out-of-phase) conditions were compared to specimens tested under isothermal conditions (T{sub min} and T{sub max}) for different {Delta}K{sub eff} levels. The dominant TMF cracking mechanisms were mechanical fatigue (crack tip plasticity) and oxygen-induced embrittlement. The {Delta}K{sub eff} was found to be the only parameter to properly correlate all the data obtained under various testing conditions. A model is developed to predict the TMFCG rates based solely on isothermal data. The model uses a linear summation of the contributions to crack growth of the two dominant mechanisms which are active at the minimum and maximum temperature of the cycle. A discussion on the applicability of the model to predict the fatigue lives of actual components is discussed.
- Sponsoring Organization:
- Natural Sciences and Engineering Research Council of Canada, Ottawa, ON (Canada)
- OSTI ID:
- 531477
- Report Number(s):
- CONF-941159--; ISBN 0-8031-2001-X
- Country of Publication:
- United States
- Language:
- English
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