Crack closure of Ni-based superalloy 718 at high negative stress ratios

Fatigue crack growth damage mechanisms for nickel-based superalloys at high, negative stress ratios challenge classical crack tip shielding and closure concepts. Fatigue crack growth rate and crack closure for single edge notch Ni-based superalloy 718 specimens at 100 degrees C were evaluated for several stress ratios (0.5, 0.1, -1, and -2). Multiple methods were used to calculate the effective driving force for crack growth rates in region II (i.e., Paris or power law regime). The relationships between the effective driving forces, the experimentally-measured crack closure levels, and the fractographic evidence of damage mechanisms are discussed.

Automated summary

This study investigates the fatigue crack growth mechanisms in nickel-based superalloys under high, negative stress ratios, challenging the classical crack tip shielding and closure concepts. The fatigue crack growth rates and closure levels were evaluated for nickel-based superalloy 718 specimens with single edge notches at 100 degrees C under different stress ratios. Multiple methods were used to calculate the effective driving force for crack growth rates, and the relationships between the effective driving forces, experimentally-measured crack closure levels, and fractographic evidence of damage mechanisms are discussed.