Low-cycle fatigue in rotating cantilever under bending .2. Experimental investigations on smooth specimens

Low-cycle fatigue of rotating cantilever beams under both load- and deflection-controlled conditions are conducted on four grades of high-strength medium-alloy steel of hardness 280, 310, 350 and 380 HE. The cyclic stress-strain response and strain-life fatigue curves are determined. A numerical methodology derived from a recent theoretical analysis is utilized, which permits the determination of cyclic stress-strain response (n' and K') and strain-life curve of any material from its measured rotating bending data, namely: the nominal bending stress and both the vertical and horizontal deflections of a tapered rotating cantilever specimen. The cyclic strain-hardening exponent, fatigue strength exponent and fatigue ductility exponent were found to be almost constant, being 0.104, 0.074 and 0.68, respectively. On the other hand, the cyclic strength coefficient was found to increase with hardness, while the fatigue-ductility coefficient was found to increase with the corresponding true ductility. From the knowledge of the monotonic properties of the tested materials, the strain-life curves for these materials predicted by using the modified universal slopes equation were in excellent agreement with the corresponding experimental curves, in contrast with the original universal slopes equation which overestimates fatigue lives in the low-cycle regime. Copyright (C) 1996 Elsevier Science Limited.