The Influence of Several Combined High/Low Cycle Loading Parameters on the Crack Growth of a Turbine Disk Alloy

The interactive effects of high- and low-cycle loading on crack growth were evaluated for a high-temperature engine disk alloy (Inconel 718) over a wide range of low-cycle hold times, low-cycle stress intensity factor range (ΔK), high-cycle ΔK, and high-cycle frequency up to 1825 Hz. A series of fatigue crack growth experiments were carried out with a constant low-cycle ΔK and an increasing high-cycle ΔK. The high-frequency ΔK and crack length were measured with sufficient precision to capture details of the transition from the low-cycle dominated regime to the high-cycle dominated regime. In these experiments, the low- and high-cycle dominated growth regimes remained distinct over the entire range of low cycle ΔK, low cycle hold time and frequency investigated. An interactive effect apparent in the low-cycle dominated regime, was a retardation of the low-cycle growth rate when high-cycle loading was applied. The degree of retardation varied with low-cycle ΔK and frequency.