A physical model and constitutive equations for complete characterization of S-N fatigue behavior of metals

The manuscript presents a new approach to the characterization of metal fatigue-the successful development of physically based law for metal fatigue from the macroscopic behavior of crack growth in CCT and SEN specimens (left). The developed equations describe quite accurately a large number of fatigue data (right) including ultra-high-cycle fatigue, effects of several fatigue-strengthening mechanisms and the effects of mean stress on the fatigue limit. It mathematically supports the existence of asymptotic nature of the endurance limit in fatigue, helping to resolve a long-standing debate of whether there exists an endurance limit or not, in fatigue. The work also provides a single master function that enables predictions of S-N behavior for any mean stress, on the basis of fully reversed fatigue data. Remarkably, unlike the empirical Goodman/Gerber equations in fatigue, the mean stress dependence is shown to naturally evolve from the behavior of material/microstructure itself, without any empiricism.219