Fatigue lifetime of ADI from ultimate tensile strength to permanent fatigue limit

Abstract

S-N curve of austempered ductile iron was obtained in the range of lifetime including low cycle fatigue domain and high cycle fatigue domain up to 108 cycles. Ultimate tensile strength is used as a limiting value of the curve. Symmetric push-pull fatigue and tensile tests were performed at room temperature on isothermally treated nodular cast iron alloyed with copper and nickel having positive impact on mechanical, technological and fatigue properties of austempered ductile iron. Suitable functions for the fit of experimentally determined points were tested and their parameters were calculated. The best results were obtained using the Palmgren function and the function introduced by Kohout and Věchet. Since the loading frequency in high-cycle region is two orders higher than in low-cycle region, the effect of loading cycle frequency on fatigue behavior of the studied material is also studied. A possibility of discontinuity of experimental data between low-cycle and high-cycle regions is discussed.