Extensive laboratory testing of typical alloys used in gas turbine blading has shown that there is a strong interaction of the thermal fatigue and creep damage modes which is nonlinear in nature. Consequently, a model for cumulative damage analysis was developed using an exhaustion of ductility concept in which the total available ductility is derived from baseline thermal fatigue tests or, alternatively, estimated from stress-rupture tests. A cycle-by-cycle reckoning of ductility used and remaining is made with the use of a digital computer program, and cracking is ultimately predicted at the point where the remaining ductility is insufficient to complete another cycle.
The developed analysis is shown to correlate with laboratory test results. The understanding and design procedure developed make it possible to simulate complex service conditions in digital computer programs and evaluate designs and materials in simulated “fly offs.”