13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- Figure 6. Fracture surfaces of structured samples. (a) Overview of four different specimen: (1) N = 1.75x106, σmax = 90 MPa, (2) N = 3.35x10 8, σ max = 90 MPa, (3) N = 5.19x10 6, σ max = 110 MPa, (4) N = 1.83x10 8, σmax = 90 MPa. Red arrows indicate crack initiation sites for samples with multiple crack initiation. (b) – (f) SEM images with higher magnification, showing crack initiation sites in detail. 5. Microscopy Fig. 4 shows SEM images of a typical fatigue fracture of a bare sample at nearly 109 cycles. The fracture origin is located close to the surface inside the material. A magnified view of the crack initiation site is presented in Fig. 4(b). Bare samples typically show single crack initiation sites in
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