Relation between Stresses for the Boundaries of Scale Levels of the Fatigue Diagram and Difference of the Meso- and Macroscale Fracture Mechanisms

Abstract— Statistical data analysis was performed based on the results of standard tests with metallic materials. The relation was found between the so-called fatigue limit, which is considered as the boundary between micro- and mesoscale fatigue fracture processes, and mechanical characteristics under monotonic tension. Using heat-resistant alloy EI698 and titanium alloy VT22 as examples, it was shown that the mechanisms of fatigue crack initiation and growth in materials with different ratios of fatigue limit to yield stress are different. The mechanism of slip band formation determines the fatigue crack initiation and its early growth stage for materials with the σ_–1/σ_0.2 ratio close to 1 and higher, as was shown for EI698. For materials with the σ_–1/σ_0.2 ratio below 1, the fatigue crack initiation is associated with mechanisms other than slipping, as demonstrated for VT22.