PSI - Issue 39

Jesús Toribio et al. / Procedia Structural Integrity 39 (2022) 560–563 Author name / Procedia Structural Integrity 00 (2021) 000–000

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3. Macro-crack paths In the macro-fractographs obtained by fatigue and posterior fracture of the wires, the crack front evolution was observed. Both the hot rolled bar and the cold drawn wire exhibit an elliptical crack front, as shown in Fig. 3.

Fig. 3. Crack shape evolutions in steel wires E0 (hot rolled bar) and E7 (cold drawn wire). Steels with intermediate drawing degree exhibit a retardation of fatigue crack growth in the central area of the wire section (Fig. 4) due to the presence of compressive residual stresses in that core area affecting the fatigue crack growth (Toyosada et al ., 1997, Vasudevan et al ., 2001; Cai and Shin, 2005) and producing a gull -shaped crack front. In the hot rolled bar (not cold drawn at all) and in the fully drawn wire (commercial prestressing steel wire which has undergone a stress-relieving process) the retardation effect ( gull -shaped crack front) does not appear (cf. Fig. 3).

Fig. 4. Crack shape evolutions in intermediate steps (from left to right, steels E2, E4 and E6).

4. Micro-crack paths Fatigue micro-cracks are trans-colonial and trans-lamellar, with non-uniform crack opening displacement, micro discontinuities, branchings, bifurcations and local deflections, creating microstructural roughness (Figs 5 and 6.).

Fig. 5. Fatigue micro-crack paths in pearlitic steel (from left to right, steels E0, E2 and E6).

Fig. 6. Sketches of the fatigue crack paths in the hot rolled bar E0 (left) and the cold drawn wire E7 (right).