PSI - Issue 28

Mihaela Iordachescu et al. / Procedia Structural Integrity 28 (2020) 39–44 Mihaela Iordachescu et al./ Structural Integrity Procedia 00 (2020) 000–000

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Fig. 6. SEM images of peripheral wires from the un-sheathed section of strands: a) in service fracture; b) SCC-CL fracture; c) in service, secondary crack: d) SCC-CL secondary crack. 4. Macro and micro mechanisms of failure Fig. 6a and Fig. 6b illustrate the fracture similarity of one of the peripheral strand-wires broken in-service with that of a SCC-CL tested wire (Fig. 8c), previously damaged in-service. Both are fragile ruptures without plasticization, with the only difference being given by the distinct oxidation of the fracture surfaces, attributed to the exposure time of the first wire in the aggressive environment after breaking. Fig. 6c and Fig. 6d illustrate the secondary cracks found in the longitudinal sections of two wires close to their fracture surfaces: the first broken in service and the second in SCC-CL. In both cases, these cracking processes were interrupted by the wire failure in an analogous process. The cracking micro-mechanisms, also the same, entailed the pop-in rupture in tension of the cementite lamellas during the hydrogen absorption in the adjacent, fragilized ferrite matrix. The only significant difference between the two secondary cracks is associated with the exposure time to the aggressive environment, explained by the corrosion products presence on the service crack faces. 5. Conclusions The lack of sheath-protection in the strand sections where the ruptures occurred, together with the environmental conditions to which they were exposed, point out to a localized, assisted damage process as a failure cause. The Zn coating was the only protective barrier of the strand-wires during service, with direct contact for a long period of time with the aggressive medium inducing severely and heterogeneously damage that propitiates the stress corrosion cracking of the wire steel. The stress corrosion tests and the failure analysis show that similar fracture mechanisms govern the progressive cracking of the strand-wires regardless of service or laboratory rupture. Acknowledgements The authors gratefully acknowledge the financial support received from Ministry of Science and Innovation in Spain (RTI2018-097221-B-I00) and of FHECOR – Ingenieros Consultores S.A. for its support and supply of the tested materials. References Álvarez J. A., Lacalle R., Arroyo B., Sainz-Aja J., Sosa I., Alonso A., 2017. Analysis of the environmental degradation effects on the cables of La Arena bridge (Spain). Procedia Structural Integrity 5, 55-62. BBR HiAm CONA. Strand stay cable system. BBR VT International, 03.2009, www.bbrnetwork.com DYWIDAG multistrand stay cable systems, 2017. DYWIDAG-SYSTEMS International, 04 178-1/07.17 -web sc, dywidag-systems.com/emea EHE 2008. Instrucción de Hormigón Estructural. Ministerio de Fomento (Structural Concrete Code, Ministry of Development), Spain FIB bulletin 30, Acceptance of stay cable systems using prestressing steels, FIB 2005, ISSN 1562-3610. Iordachescu M., De Abreu M., Valiente A., 2015. Effect of cold-drawn induced anisotropy on the failure of high strength eutectoid and duplex steel wires. Eng Fail Anal 56, 412-421. Iordachescu M., De Abreu M., Valiente A., 2018. On hydrogen-induced damage in cold-drawn lean-duplex wires, Eng Fail Anal 91, 516-526. Parrondo Rodríguez J., 2017. El hundimiento del puente de la carretera M-527 sobre el río Guadarrama. Revista de Obras Públicas (The collapse of the M-527 highway bridge over the Guadarrama river. Public Works Journal), no. 3583, 74-95 . prEN 10138-2, 2009. Prestressing Steels–Part 2:Wires CEN. Toribio J., Valiente A., 2006. Failure analysis of cold drawn eutectoid steel wires for prestressed concrete. Eng Fail Anal 13, 301–11.