PSI - Issue 39

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

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The cold drawn wire exhibits a fatigue crack path with more micro-deflections than the hot rolled bar (Fig. 6), the micro-deflection path being shorter and the micro-deflection angle being higher in the former than in the latter, i.e.,

(0) (7) θ θ <

(1) (2)

(0) (7) d d >

Thus the frequency of deflections in the fatigue crack path increases with the cold drawing (Fig. 6). This tortuous crack path is one explanation of the improvement of fatigue performance in the cold-drawn wire when compared to that of the hot rolled bar (Toribio and Toledano, 1999; Toribio et al ., 2007a, 2007b).). 5. Conclusions In the matter of macro-crack paths , fatigue crack growth in pearlitic steel wires under tensile loading in the Paris regime develops in global mode I with an elliptical crack front ( macro-crack path ). The steel wires with an intermediate cold drawing degree exhibit a retardation related to crack growth at the crack front center ( gull effect ) due to the presence of compressive residual stresses in the central area of the crack front that delay crack advance. With regard to micro-crack paths , the fatigue cracks are trans-colonial and trans-lamellar (crossing the colonies and breaking the lamellae). The crack opening displacement is not uniform, and many micro-discontinuities, branchings, bifurcations and local deflections appear, the latter especially in the most heavily cold drawn steels. Thus the cold drawing process produces a tortuous micro-crack path delaying fatigue crack growth. References Cai, C.Q. and Shin, C.S., 2005. A normalized area-compliance method for monitoring surface crack development in a cylindrical rod, International Journal of Fatigue 27, 801-809. Gray III, G.T., Thompson, A.W. and Williams, J.C., 1985. Influence of microstructure on fatigue crack initiation in fully pearlitic steels, Metallurgical Transactions 16A, 753-760. Korda, A.A., Mutoh, Y., Miyashita, Y. and Sadasue, T., 2006a. Effects of pearlite morphology and specimen thickness on fatigue crack growth resistance in ferritic-pearlitic steels, Materials Science and Engineering A428, 262-269. Korda, A.A., Mutoh, Y., Miyashita, Y., Sadasue T. and Mannan, S.L., 2006b. In situ observation of fatigue crack retardation in banded ferrite pearlite microstructure due to crack branching, Scripta Materialia 54, 1835-1840. Ravichandran, K.S., 1991. A rationalisation of fatigue thresholds in pearlitic steels using a theoretical model, Acta Metallurgica et Materialia 39, 1331-1341. Toribio, J. and Ovejero, E., 1997. Microstructure evolution in a pearlitic steel subjected to progressive plastic deformation, Materials Science and Engineering A234-236, 579-582. Toribio, J. and Ovejero, E., 1998a. Microstructure orientation in a pearlitic steel subjected to progressive plastic deformation, Materials Science Letters 17, 1037-1040. Toribio, J. and Ovejero, E., 1998b. Effect of cumulative cold drawing on the pearlite interlamellar spacing in eutectoid steel, Scripta Materialia 39, 323-328. Toribio, J. and Ovejero, E., 1998c. Effect of cold drawing on microstructure and corrosion performance of high-strength steel, Mechanics of Time Dependent Materials 1, 307-319. Toribio, J. and Toledano, M., 1999. Fatigue behaviour of progressively drawn steels, Proceedings of the Seventh International Fatigue Congress (Wu X.R. and Wang Z.G., editors), Beijing, June, EMAS, West Midlands. Toribio, J., González, B. and Matos, J.C., 2007a. Fatigue crack propagation in cold drawn steel, Materials Science and Engineering A468-470, 267 272. Toribio, J., González, B., Matos, J.C. and Ayaso, F.J., 2007b. Micro- and macro-approach to the fatigue crack propagation in high-strength pearlitic steel wires, Key Engineering Materials 348-349, 681-684. Toyosada, M., Niwa, T. and Sakai, J., 1997. Physical meaning of ∆ K RP and fatigue crack propagation in the residual stress distribution field, International Journal of Fatigue 19, S161-S166. Vasudevan, A.K., Sadananda, K. and Glinka, G., 2001. Critical parameters for fatigue damage, International Journal of Fatigue 23, S39-S53.