Francis J. Clauss, James W. Freeman
An experimental study was made of the effect of the following factors on the life of two ductile alloys (S-816 and Inconel 550) under high-temperature thermal-fatigue conditions: (1) The maximum cycle temperature, T-sub-max, (2) The temperature difference of cycling, delta-T = T-sub-max - T-sub-min, (3) The cyclic time of exposure at the maximum cycle temperature, t at T-sub-max, and (4) the cyclic plastic strain. Tensile specimens of S-816 and Inconel 550 were alternately heated and cooled while constrained in a manner that prevented their free axial expansion and contraction, and the number of cycles to fracture was determined. Hardness measurements and microstructural studies were made. For the materials and test conditions studied, the following conclusions were drawn: The number of cycles to failure was more sensitive to changes in the maximum cycle temperature than to changes in the temperature difference.
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