Observations of the Effect of Creep Relaxation on High-Strain Fatigue

Abstract

Results are presented of high-strain endurance tests on 2‡ per cent chromium, 1 per cent molybdenum steel. As well as continuous cycling at room temperature and 600°C, the tests covered hold times of 30 minutes and 300 minutes at maximum strain at 600°C. For the shorter hold times, strain ranges extended down to less than ±0.1 per cent and for the longer hold times down to ±0.24 per cent. In a few tests an attempt was made to modify the test environment in order to gain an indication whether corrosion effects are likely to be important in such tests. It is argued that, for preliminary design purposes (pending the outcome of comprehensive endurance tests), extrapolation from high strains to low may be dangerous and that it may be preferable to use relatively simple creep data to gain an early indication of likely endurance properties with hold time. Such an interpretation is not inconsistent with the present or previously published data.