低炭素鋼の熱疲労強度に及ぼす平均温度と温度変動幅の影響

抄録

Many criteria for thermal fatigue failure have been proposed, but almost all of them seem to be little authorized. Both the combined effects of temperature and strain as well as the wide variations of test methods make it difficult to find a general rule.
In order to evaluate the effect of temperature on the relation between the plastic strain range and the number of cycles to failure, the authors carried out thermal fatigue tests with a low carbon steel at three different mean temperature levels and temperature ranges. The experimental results were compared with the predicted life of the materials obtained from the low cycle fatigue data at constant elevated temperatures.
The test system contains a newly-devised extensometer and a servo-control equipment. It can change the strain ranges independently from the temperature ranges, while keeping the proportionality between instantaneous strain and temperature constant.
The results obtained are summarized as follows:
(1) The relation between the plastic strain range Δε_p and the number of cycles to failure N_f under fixed T_max and T_min can be described by Δε_p·N_f^β=const., where β is a constant much greater than 0.5.
(2) Both the increase of mean temperature level and the increase of the temperature range give the same effect on the decreasing fatigue life of low carbon steel under the present test conditions.
(3) The life predicted from low cycle fatigue at elevated temperatures under the assumption of linear damage theory coincides with the experimental values at relatively low temperatures, but it is more than the experimental values at temperatures higher than 450°C in the case of low carbon steel.