"Linking fatigue strength to plastic localization in polycrystalline materials"
Surprising relations exist between the fatigue strength of metallic materials and their intrinsic monotonic mechanical properties such as yield strength (YS), ultimate tensile strength (UTS) and hardness. High YS metals display significantly low fatigue strength to UTS ratios. Conversely, metals with low YS generally display fatigue strengths that approach or are above their YS. The physical intrinsic processes and parameters at the microstructure scale that link the YS and UTS to fatigue strength are not yet clearly identified. Plastic localization is investigated as a function of the microstructure to elucidate these relations.
Systematic and quantitative investigations of slip in various face-centered cubic (fcc), hexagonal close-packed (hcp) and body-centered cubic (bcc) metals processed using conventional and additive manufacturing routes have been performed over large microstructural representative field of views using high-resolution digital image correlation. Multimodal analyses (plastic localization as a function of the microstructure) were systematically performed on very large number of slip events, to quantify the aptitude of metals to accommodate plastic deformation during monotonic and fully reverse loading. A correlation between the YS, fatigue strength and the amplitude of slip localization during monotonic loading is observed, elucidating the surprising relations between the intrinsic monotonic mechanical properties and fatigue strength. While slip localization in fcc and hcp metals are observed to behave similarly to a certain extend, slip localization in bcc metals displays unusual behavior that explains the general observation that bcc metals over-perform fcc and hcp metals in fatigue.
