SUMMARY

Industrial gas turbine engines expose hot-section turbine components to extreme environments characterized by high temperatures, sustained and cyclic loads, and corrosive environments. Creep, fatigue, damage, crack growth, and fracture are thus critical design considerations for these components. Ni-base superalloys, known for their high strength and creep resistance, are commonly used for turbine blades. Turbine blade designers face the challenging question of determining whether to remove a cracked hot-section turbine engine blade from service, and they must select an appropriate service life estimation scheme for creep or creep-fatigue loading conditions when a macroscopic crack is present. Single value fracture mechanics-based approaches are preferred for characterizing crack growth and estimating service life, but it is unclear whether these techniques should be applied in these situations because of the loading conditions and heterogeneity of the material. Experiments revealed that in directionally-solidified Ni-base superalloys, creep and creep-fatigue crack growth behavior perpendicular to the solidification direction does not fit the context of single-parameter fracture mechanics when significant damage in the form of secondary cracks and microcracks accumulates near the crack tip. The amount and extent of damage is heavily influenced by temperature, stress state, applied load levels, and component size relative to key microstructural features. Therefore, limits are established for the applicability of fracture mechanics-based techniques, and service life estimation approaches are recommended based on observations of the crack growth behavior. Join Zoom Meeting - https://gatech.zoom.us/j/94656797280?pwd=UHg3SWpIaTdrekRnOVdIbUIzK1hKQT09 Meeting ID: 946 5679 7280 Passcode: 140292