試作高温疲労試験機と低炭素鋼の高温疲労

抄録

Rotary bending test is the easiest to carry out among various sorts of testing method of fatigue, and is often practised for determining fatigue characteristics of metallic materials. For fatigue tests at elevated temperatures, rotating load type machine is more preferable to rotating specimen type in order to achieve accurate measurement of specimen temperature. A rotary bending fatigue testing machine of rotating load type for tests at elevated temperatures was designed and manufactured. A brief description on the machine is rendered in this paper.
The original intention of the present study is to discuss the influence of frequency of stress cycles on fatigue life of heat resistant alloys at elevated temperatures. As a preliminary study for it, fatigue of low carbon steel at elevated temperature of 450°C was investigated by applying three sorts of stress cycles, 170, 750 and 3000per min., using the new testing machine. Each test was carried out under the condition of constant strain amplitude.
The results of the tests are summerized as follows; as far as the strain amplitude applied is large, the number of stress cycles till fracture is not affected by the frequency of applied cyclic stress and so, under the action of the definite magnitude of strain amplitude, specimens fracture at definite number of stress cycles. When the strain amplitude is small, however, specimens are likely to fracture at definite time notwithstanding different frequency of stress cycles imposed. The intermediate feature of fracture is apparent in the test under strain amplitude between both extremes which lead to the results contradictory to each other.
The mechanism of fatigue at elevated temperatures is discussed by taking inelastic deformation in every stress cycles, which depends on frequency of stress cycles, as operative factor on fatigue. The qualitative interpretation of the experimental results is given.