FATIGUE-CRACK GROWTH IN 2 ADVANCED TITANIUM-ALLOYS UNDER CONSTANT ANDVARIABLE AMPLITUDE LOADING AT 25 AND 175 DEGREES-C

Fatigue crack growth of beta-21S and Ti-62222 in sheet form was invest igated under constant and miniTWIST flight spectra loading conditions at 25 and 175 degrees C. Variable amplitude results were compared with life calculations performed using NASA/FLAGRO software and constant a mplitude fatigue crack growth results. Single tensile overloads under constant Delta K were performed to evaluate load interaction effects. Constant amplitude results showed that fatigue crack growth resistance was slightly better for Ti-62222 than beta-21S at 25 and 175 degrees C. The presence of crack closure under various conditions caused moder ate shifts in the fatigue crack growth data. Under miniTWIST flight sp ectra loading, Ti-62222 exhibited a greater extension in life in compa rison to the beta-21S at elevated temperature, consistent with the NAS A/FLAGRO calculations. This was also consistent with the single tensil e overloads where 25 degrees C tests were comparable for both material s, while at 175 degrees C, delay cycles were greater by a factor of al most three for Ti-62222. Extensive secondary cracking in Ti-62222 at e levated temperature accounted for the extended fatigue lives.