PSI - Issue 54

Maricely De Abreu et al. / Procedia Structural Integrity 54 (2024) 143–148 De Abreu M. et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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to the diameter measurements is well below the tensile strength of the steel (1800 MPa), while in the second case the geometrical irregularities contained in the surface of the wire just accelerate the necking process, with no effect on the wire other than the mere loss of resistant section. The four tested wires fit the above-described behaviors. 3. Damage tolerance A quantitatively conclusive method for confirming that the cross-section loss is the only structurally relevant effect of the damage experienced by the steel wires involves comparing the breaking loads of the tested wires with the tensile load that would plastically collapse the resistant ligaments (De Abreu et al., 2018). Fig. 3a shows the scanning electron microscopy (SEM) images of the cross sections of the in-service damaged wires broken in tension in the laboratory, with a resistant area previous to testing highlighted in Fig. 3a. These were measured by using an image analysis program for further use in the damage tolerance diagram.

Fig. 3. a) Resistant cross-sections of in-service damaged wires broken in tension in the laboratory; b) Damage tolerance of studied steel wires: experimental results and theoretic limits of plastic collapse.

Fig. 3b is a damage tolerance diagram for steel wires, in which the tensile breaking load P m is represented against the resistant cross-section loss A f , respectively plotted in dimensionless terms through P 0 and A 0 , namely the breaking load and resistant cross-section in absence of damage (in this particular case, a circular cross-section of 5.0 mm diameter and its corresponding tensile bearing capacity of 35.3 kN, for the measured tensile strength of 1800 MPa). The two curves added to the diagram are theoretical plastic collapse curves of the resistant ligament based on the stress limit states schematized in Fig. 3b and an ideal yield strength equal to the measured tensile strength R m of 1800 MPa. The eccentricity of the resistant area with respect to the wire axis is zero in the case of the straight line and maximum in the curved line, since the cross-section losses are concentrated towards the same side of the lateral surface of the wire. The loading mode to which the cross-section is subjected ranges from simple tension to combined bending and tension. The test results occupy four points on the diagram of Fig 3b between these two lines. The results are consistent with the absence of damage able to favor failure types that are anticipating the plastic collapse of the wire specimens. Consequently, this entails the stress concentrations beaing induced by the highly irregular cross-section losses along the wires become plastic deformation concentrations before local hydrogen uptake and steel embrittlement attain levels enough to cause assisted cracking. 4. Damage mechanisms The two failures showing low ductility in Fig. 2b suggest the action of an aggressive environment able to embrittle the steel when combined with tensile stresses. This combination gives rise to a progressive cracking process due to localized corrosion and embrittlement of the steel, (Toribio et al., 2006). The stress level of the