13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- dependence the crack length on the normalized and the absolute number of tension cycles were calculated and plotted. Much like to the case of LCFat comparisonthe graphs of specimens without treatment and after the surface nanostructuring differences in time of the main crack origination, as well as the rate of its development becomes visible. Crack growth rate of the specimens without treatment made0.03 µm/cycle, while for one with the nanostructurized surface layer its rate is reduced by 2 times that can be estimated as 0.015 µm /cycle. 2.4.3. Fractography study of cyclically fractured specimens 12Cr1MoV Micrographs of specimens fractured under cyclic tensile were obtained using scanning electron microscope at high magnification (fig. 3). Micrographs gained in fatigue crack growth region (fig. 3, b) also point to the brittle pattern of the nanostructured surface layer fracture being compared with untreated specimens (fig. 3, a). It is seen that the surface layer of the nanostructured specimen is damaged by multiple cracks that does not bring to noticeable deformation localization. According to the author’s opinion, multiple cracking allows to redistribute efficiently the loading and minimize the effect of the powerful stress macroconcentrator operating in the vicinity of the main fatigue crack tip. а) b) Figure 3. SEM micrographs for the area of fatigue crack growth found at the flat face failured at cyclic tension tests; (а) specimens without treatment; b) with nanostructured surface layer; axis of loading oriented vertically 2.4.4. High-cycle fatigue (HCF) 30CrMnSiNi2
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