Abstract
Since fatigue strength at very high cycles has been found to decrease drastically in some high-strength steel, it has become very important to establish a very high cycle fatigue test using ultrasonic loading because of its reasonable short test time. However, there are two issues: self-heating of specimen and load frequency effect. It was confirmed that the temperature of a specimen increased with the square of the applied amplitude of displacement. The combination of the forced air cooling and intermittent loading was effective for minimizing the increase of the specimen temperature within 50℃. Load frequency effect was observed in the ultrasonic fatigue test of Mod.9Cr-1Mo steel.
