Effects of Stress Ratio and Hold-Time on Fatigue Crack Growth in Alloy 718

[+] Author and Article Information
P. Shahinian, K. Sadananda

Thermostructural Materials Branch, Material Science and Technology Division, Naval Research Laboratory, Washington, D.C. 20375

J. Eng. Mater. Technol 101(3), 224-230 (Jul 01, 1979) (7 pages) doi:10.1115/1.3443681 History: Received January 01, 1979; Online August 17, 2010


Crack growth rate da/dN in Alloy 718 at 650°C, compared on the conventional ΔK basis, increased with increase in R (Kmin /Kmax ) and also generally with inclusion of hold time at Kmax and Kmin . An exception, however, was that a 1-min hold at a Kmin just below the threshold K for creep crack growth caused retardation of crack growth. Correlation of da/dN for various R levels was better with Kmax than with other parameters such as Kmin , ΔK, and Δ J-integral. Fatigue crack growth in the alloy was found to be time dependent and Kmax controlled under these test conditions and consequently the best overall correlation was given by da/dt with Kmax . An unusual observation was that the addition of hold time to the loading cycle at near zero Kmin (R = 0.05) caused an increase in da/dN, as the result of an environmental interaction.

Copyright © 1979 by ASME
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