Thermal Fatigue and Cyclic Mechanical Strain Fatigue at Elevated Temperature of 18-8 Cb Stainless Steel and 2.25 Cr-1 Mo Steel

Abstract

Thermal fatigue strength was analysed from the data of cyclic mechanical strain fatigue tests at fixed temperatures on the basis of the fundamental equation which has been formulated by the authors in connection with fatigue damage. In order to relate the thermal fatigue strength with the cyclic mechanical strain fatigue strength, an equivalent steady temperature was introduced. According to the analysis, the equivalent steady temperature is approximately equal to the mean of upper and lower temperature levels of cyclic variation of temperature in the case of a large strain amplitude where the plastic strain is predominant as compared with the elastic strain. However, in the small strain range where the elastic strain plays a main role, the equivalent steady temperature is rather close to the upper temperature level. Experimental data with 18-8 Cb stainless steel and 2.25 Cr-1 Mo steel were exhibited to confirm the above statement.