13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Fig.7. The form of zones of intense energy dissipation in the crack tip on the first cycle of deformation and plastic deformation zone, built on the criteria of von Mises and Tresca-Saint Venant. 5. Fractography analysis of fractured specimens. Fractured specimens were investigated by optical and scanning electronic microscopes for qualitative analysis of fracture surface. Specimens with inside and surface crack initiation were observed. For quantitative analysis was used interferometer profiler New View 5010 which can get 3D image of investigated surface with digital data. Relief of fractured surface close to crack initiation and its propagation was analyzed. Fig 8. Typical relief of fractured specimen with inside crack initiation obtained on interferometer profiler New View. In the study, one-dimensional image of the of the relief in certain selected sections, were analyzed by the method of Hurst in terms of the Hurst exponent, measured by the correlation function: H x x x r x x r r K r Maxzx Min zx ∝ − = + + ( ( )) ( ( )) ( ) { , } { , } , (9) where z (x) - the height of the relief, depending on the coordinates, the angle brackets denote averaging over x, H - Hurst exponent. In terms of Hurst exponent fractured relief had 2 zones with significant difference of H. First zone has circle geometry and its position around crack initiation with diameter ~ 300 µm. We assume that inside this zone was defect accumulation during fatigue loading. When this zone reach 300 µm diameter crack became instability and start propagate and we can see it on increasing of H. Second zone size reach cross section of specimen.
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