PSI - Issue 62

Silvia Caprili et al. / Procedia Structural Integrity 62 (2024) 355–360 Caprili et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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extensometer instrumentation for data acquisition (Fig. 1). A tensile machine with 500 kN of capacity was used.

Fig. 1. Tensile tests: general set - up and adoption of video extensometer.

Two different failure modalities were observed, in the following called ‘ bird cage ’ failure modality – associated to a strand level ductile performance with high level of achieved deformation and characterized by the simultaneous crack of all the 7 wires in almost the same section, and the ‘wire -by- wire’ (or progressive) failure modality, associated to a more brittle performance and to lower level of the achieved deformation (Fig. 2 a,b). The load – deformation curves of corroded strands well reflect what said above, with higher decrease of the mechanical features in the second case (progressive). Fig. 2 also shows the comparison between uncorroded and corroded strands ’ performance in relation to the two failure modalities. The bird-cage modality leads to a small reduction of ultimate strength and deformation capacity respect to uncorroded case, while the wire-by-wire modality shows typical drops associated to the progressive failure of single wires.

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(b)

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Fig. 2. a) Load-strain diagrams; b) bird-cage and c) wire-after-wire failure modality.

Analysing the results of tensile tests, the majority of the samples, about 70%, present a wire-by-wire failure modality, underling the effects of corrosion and tenso-fragility phenomena due to HE. Furthermore, over 30% of the tested strands is not able to satisfy the standards’ requirements for, at least, one of the required minimum values according to Italian standard D.M.17/01/2018 (i.e. ultimate tensile strength, strength corresponding to 1% deformation, elongation to maximum load). Bending/re-bending tests were executed according to the prescription of EN 10218-1:2012 and SIST-ISO7801-1996 on about n.250 wires, with the aim to evaluate their toughness: according to the results, in this case, only 4% of wires do not