Low cycle fatigue hold time behavior of cast rené 80

Strain-time programs involving continuous cycling, equal hold times in tension and compression, tensile strain hold periods, and compressive strain hold periods are compared for cast René 80 at 1600°F. It was found that the predictive equations for high-temperature fatigue give good agreement with experiments in which the hold times are equal. Contrary to expectation, however, tensile strain hold experiments gave longer liver than predicted, wile compressive strain hold period experiments were shorter than the predictions. Concurrently, the hysteresis loops from these two sets of experiments exhibited pronounced and opposite mean stresses, the tensile strain hold tests showing a compressive mean stress shift. These shifts were explainable in terms of the times spent in tensile and compressive loading, and could account qualitatively for the observed life behavior.