1966 年 15 巻 156 号 p. 589-594
By means of the previously mentioned thermal fatigue testing machine of high-frequency induction heating and water cooling type, this study was performed to as certain the effect of the amplitude of temperature variation on the thermal fatigue life of 18-8- and 13 Cr steels under conditions of transient temperature gradient.
The results obtained in comparison with Coffin's type thermal fatigue data are summarized as follows:
(1) In the case of thermal fatigue under conditions of transient temperature gradient, the compressive strain which had been introduced on the heated surface in the heating process was reduced gradually during the holding time at elevated temperature, and then in the cooling process, it turned into the tensile strain. The higher the temperature on the heating surface rose, the larger the reduction of the compressive strain and the tensile strain became.
(2) When this compressive strain decreased, it was considered that there was tensile stress on the heated surface. By this tensile stress at elevated temperature, the thermal fatigue life of 18-8 steel on the amplitude of temperature variation of 600 deg (C) showed about one-tenth of Coffin's type thermal fatigue life.
(3) But, in the thermal fatigue under conditions of transient temperature gradient, it showed that between the total strain range and the number of thermal cycles to the definite crack length, there was the same linear relationship in logarithmic coordinate as Coffin's type thermal fatigue data.