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Effect of Stress Variation on Creep of a Super Alloy at Elevated Temperatures

Report Number: ML TDR 64-166
Author(s): Ryoichi Koterazawa
Corporate Author: University of Minnesota
Laboratory: AF Materials Laboratory
Date of Publication: 1964-06
Pages: 64
Contract: AF 33(657)-7453
Project: 7351 - Metallic Materials
Task: 735106 - Behavior of Metals
AD Number: AD0603058

Abstract:
An investigation was conducted to evaluate the effect of cyclic stress on the creep of a super alloy at elevated temperature. Special attention was given to the frequency effect, and experiments were carried out for a wide range of frequencies, from one cycle per day to 300 cycles per minute, where test data are lacking. Results of experiments showed that there is a relatively narrow transient range of frequencies where the effect of frequency is large and that this transient range shifts quite regularly with the change of stress and temperature, a shift to a higher frequency is caused by higher stress level, lower stress ratio or higher temperature. As expected, the strengthening of material by cyclic stress was found to be an important controlling factor of this phenomenon. However, another factor, recovery effect, was found to be more significant. Some deteriorating of the material was observed in the case where the rest period is much larger than the loading period. Also, cycle dependent fatigue damage was observed in the case of high alternating stress at high frequency.

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