On the origins of fatigue strength in crystalline metallic materials.

Metallic materials experience irreversible deformation with increasing applied stress, manifested in localized slip events that result in fatigue failure upon repeated cycling. We discerned the physical origins of fatigue strength in a large set of face-centered cubic, hexagonal close-packed, and body-centered cubic metallic materials by considering cyclic deformation processes at nanometer resolution over large volumes of individual materials at the earliest stages of cycling. We identified quantitative relations between the yield strength and the ultimate tensile strength, fatigue strength, and physical characteristics of early slip localization events. The fatigue strength of metallic alloys that deform by slip could be predicted by the amplitude of slip localization during the first cycle of loading. Our observations provide a physical basis for well-known empirical fatigue laws and enable a rapid method of predicting fatigue strength as reflected by measurement of slip localization amplitude.