Abstract
Thermal fatigue strength was analysed from the data of cyclic-strain fatigue tests at constant temperature on the basis of the fundamental equation which had been proposed by the authors in connection with fatigue damage. In order to relate thermal fatigue strength with cyclic strain fatigue strength, an equivalent temperature was introduced as a steady temperature at which material endures the same strain amplitude for the same life as under thermal fatigue condition.
According to the analysis, the equivalent temperature is approximately equal to the mean temperature in the case of large amplitude where plastic strain is predominant as compared with the elastic strain. However, in the small strain range where elastic strain plays a main role, the equivalent temperature would be close to the maximum temperature. Experimental data with a 18-8 stainless steel was exhibited to confirm the above statement.
The strain localizing effect due to non-uniform distribution of temperature along specimen was also discussed, and the difference between thermal fatigue and mechanical fatigue strength found in literatures was interpreted from the strain localizing effect in thermal fatigue tests.
