Evaluating the thermal fatigue strength of full-scale gas-turbine-engine blades

Conclusions

• 1. The use of well-known equations obtained on the basis of results of tests of specimens of a broad class of materials to evaluate the thermal fatigue life and safety factors of full-scale cooled turbine blades may lead to substantial errors. To more correctly evaluate the safety factors, it is necessary to use the results of tests of full-scale blades under conditions near or equivalent to service conditions.

• 2. Blade fracture is determined not only by the amplitude of the elastoplastic deformation in the loading cycle, but also by the maximum temperature of the cycle and the character of the deformation (sign-changing or sign-constant cycle). A sign-changing loading cycle inflicts more damage than a sign-constant cycle with the same or somewhat greater strain amplitude.

• 3. The performance of full-scale blade tests makes it possible to account for design features and to determine the reason for the origination of defects in service, as well as to develop measures to eliminate these defects.