Abstract
Previously, some of the present authors conducted experiments on the fatigue creep of various kinds of steel and brass under bending, torsional and axial stress at room temperature, and clarified various features of the fatigue creep of these materials.
This report is on our study concerning the fatigue creep of 0.21%C carbon steel at a temperature of 300°C and 500°C, for which a newly devised axial fatigue testing machine for high temperature tests was used.
Results obtained were as follows: At 300°C, a fatigue creep strain occurred to the specimen increases considerably at the early stages of fatigue, when it is subjected to a combined mean and alternating stress, and, in subsequent repetitions of stress cycles, a slight increase of strain can be observed. But the general feature of fatigue creep strain is similar to that of this material at a room temperature. Namely, the fatigue creep strain is larger than the static creep strain at the same temperature, if the comparison is made under the same maximum stress both in fatigue and static creep tests, and the fatigue creep limit takes substantially the same value of yield point in the static test at this temperature.
At 500°C, the general feature of fatigue creep strain essentially differs from that at 300°C and a room temperature. The fatigue creep strain at this temperature increases gradually with repetitions of stress cycles, and we can observe a remarkable increase of strain in the final stage of fatigue, except when the mean stress is very low. Besides, the fatigue creep strain is smaller than the static creep strain at the same temperature and under the same maximum stress, contrary to the above tendency noticed at 300°C and a room temperature. These phenomena seemed to be resulted from so-called time effect which is recognized at high temperature tests.
