Rr. Stephens et al., FATIGUE-CRACK GROWTH IN 2 ADVANCED TITANIUM-ALLOYS UNDER CONSTANT ANDVARIABLE AMPLITUDE LOADING AT 25 AND 175 DEGREES-C, Fatigue & fracture of engineering materials & structures, 21(7), 1998, pp. 819-834
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.