Thermal-mechanical fatigue crack growth in aircraft engine materials

This thesis summarizes the major technical achievements obtained as a part of a collaborative research and development project between Ecole Polytechnique and Pratt & Whitney Canada. These achievements include: (1) a thermal-mechanical fatigue (TMF) testing rig which is capable of studying the fatigue behaviors of gas turbine materials under simultaneous changes of temperatures and strains or stress; (2) an advanced alternative current potential drop (ACPD) measurement system which is capable of performing on-line monitoring of fatigue crack initiation and growth in specimen testing under isothermal and TMF conditions; (3) fatigue crack initiation and short crack growth data for the titanium specimens designed with notch features associated with bolt holes of compressor discs; (4) thermal-mechanical fatigue crack growth data for two titanium alloys being used in PWC engine components. Those data explained the material fatigue behavior encountered in full-scale component testing; (5) a complete fractographic analysis for the tested specimens which enhanced the understanding of the fatigue crack growth mechanisms and helped to establish an analytical crack growth model; (6) application of the ACPD fatigue crack monitoring technique to Single Tooth Firtree Specimen (STFT) LCF testing of PWA 1480 single crystal alloy. Finally, a comprehensive discussion concerning the results pertaining to this research project is presented.