SYMPOSIA PAPER Published: 01 January 1989

Threshold Crack Growth Behavior of Nickel-Base Superalloy at Elevated Temperature


An experimental program was conducted to evaluate the effects of frequency and R on the near-threshold crack growth behavior of Inconel 718 at 649°C in laboratory air. Frequencies from 0.01 to 400 Hz and R from 0.1 to 0.9 were applied to compact tension [C(T)] and middle- or center-cracked tension [M(T)] specimens under decreasing-K conditions using computer-controlled test machines. Digital load-displacement data were obtained to determine crack length and closure load. The fatigue crack growth threshold in Inconel 718 at 649°C obtained using decreasing ΔK testing was generally associated with a crack arrest phenomenon which could be attributed to the buildup of oxides with time. Over the ranges of R and v used in this investigation, the growth rate behavior at the onset of crack arrest appears to be a combination of time-dependent and cyclic-dependent behavior. Even at 400 Hz, purely cyclic behavior was apparently never reached. For crack growth rate modeling, both frequency and stress ratio have to be incorporated in the characterization of ΔKth. Over the ranges of parameters tested, a cyclic threshold was approached at high frequencies and low R and a sustained load time-dependent threshold was obtained at high R, indicating that the cyclic contribution to the growth rate was negligible.

Author Information

Ashbaugh, NE
University of Dayton Research Institute, Dayton, OH
Nicholas, T
Air Force Wright Aeronautical Laboratories (AFWAL/MLLN), Wright-Patterson Air Force Base, OH
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Developed by Committee: E08
Pages: 628–638
DOI: 10.1520/STP18848S
ISBN-EB: 978-0-8031-5081-2
ISBN-13: 978-0-8031-1250-6