“On the origins of fatigue strength in crystalline metallic materials”
With increasing applied stress, metallic materials experience irreversible deformation, manifested in localized slip events that result in unexpected fatigue failure upon repeated cycling. Recent advances in accelerated fatigue testing, in-situ electron microscopy, digital image correlation methods, and multi-modal data analysis have been integrated to quantitatively characterize the evolution of these slip events from the earliest stages of cycling at the nanometer scale over large fields of view in relation to material structure. Statistical analyses of slip events for a large collection of materials with face-centered cubic, hexagonal close-packed, and body-centered cubic structures have been performed. Relations between the yield and ultimate tensile strength, cyclic fatigue strength, and slip events characteristic are uncovered. It is observed that the fatigue strength of fcc, hcp, and bcc metallic alloys can be predicted by the amplitude of slip localization during the first cycle of loading. These observations provide a physical basis for well-known empirical fatigue laws and enable a rapid material design method by predicting fatigue strength via measurement of slip localization amplitude.
