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Typical fractography of single-point surface crack initiation with clear facet feature (notched specimen, R = 0.5, σa = 140 MPa, Nf = 6.048 × 107 cycles); (a) the whole fracture surface; (b) macro profile with crack initiation region and crack propagation region; (c) enlargement of crack initiation region recognized by the facet feature and separated by the dashed line; (d) enlargement of the facets, as pointed out by the arrows.
