Thermal Mechanical Fatigue Life Prediction for Advanced Anisotropic Turbine Alloys

The most severe stresses that turbine airfoils encounter are thermally induced by extreme temperature gradients and rapid thermal transients. These thermally induced stresses combined with mechanical loading produce thermal mechanical fatigue (TMF) cracking in the airfoil. Analysis of and life prediction for the complex loading situation is further complicated by the use of advanced anisotropic alloys in high turbine sections of modern aircraft engines. In an effort to better understand TMF behavior of these materials, a test program was conducted to simulate turbine airfoil conditions at critical locations. A damage parameter containing terms thought to be essential to the description of material response to TMF cycling was developed. The damage parameter consolidated the data within a factor of approximately 1.5×.