PSI - Issue 81

Jesús Toribio et al. / Procedia Structural Integrity 81 (2026) 92–94

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Previous research does exist on HE of high-strength cold-drawn pearlitic steel for prestressing wires using notched specimens (Toribio, 1992; 1993; 1996) and cracked ones (Toribio and Lancha, 1993; 1998; Toribio and Ovejero, 1999; 2001; 2007). However, in the scientific literature there is a scarcity of data on HE of smooth wires of pearlitic steel, mainly due to the big scatter of experimental results, although some classical references do exist (Cherry and Price, 1980), as well as recent ones (Hredil et al., 2015; Hredil and Toribio, 2016). In this research framework, the present paper studies the local anisotropy of HE behaviour of initially-smooth samples of cold drawn pearlitic steel wires (commercial prestressing steel wires). 2. Experimental procedure Initially-smooth samples of cold drawn pearlitic steel wires ( commercial prestressing steel wires ) were subjected to slow strain rate tests (SSRT) in aggressive environment promoted by a corrosion cell with a three electrode assembly. The test environment was an aqueous solution of 1 g/l calcium hydroxide plus 0.1g/l sodium chloride. The pH was 12.5 and tests were performed at constant electro-chemical potential ranging between – 1100 mV versus SCE and – 1400 mV versus SCE ( saturated calomel electrode ) to maintain environmental conditions associated with HE. 3. Analysis of the environmentally-assisted crack paths Figs. 1 and 2 show the transverse fracture surfaces and the fracture profiles ( crack paths ) in two wires tested respectively at faster (0.1 mm/min) and slower (0.01 mm/min) applied displacement rate (crosshead speed) under electrochemical potentials of – 1400 mV SCE and – 1200 mV SCE. The main phenomenological fact regarding crack paths is the locally anisotropic hydrogen embrittlement behaviour of high strength cold-drawn pearlitic steel wires (commercial prestressing steel wires). The local anisotropy of HE is reflected in the crack path (fracture profile) in the form of local crack deflections (Figs. 1 and 2).

Fig. 1. Transverse fracture surface and fracture profile ( crack path ) for a wire tested at 0.1 mm/min and – 1400 mV SCE.

Fig. 2. Transverse fracture surface and fracture profile ( crack path ) for a wire tested at 0.01 mm/min and – 1200 mV SCE.

4. Discussion The previous section showed evidence of micro-crack deflections, branchings and bifurcations, a signal of certain longitudinal splitting or delamination, producing a phenomenon of axial micro-cracking in the cold drawing direction (wire axis), an evidence of local anisotropy of HE behaviour in the form of local micro-crack deflections representing embryos of anisotropic fracture . The afore-said local micro-deflections are induced by the oriented pearlitic microstructure after manufacture by cold drawing (Toribio and Ovejero, 1997; 1998a; 1998b; 1998c). The embryos do not transform into real macro-crack deflections due to the lack of stress triaxiality (constraint) in the smooth wires. Axial micro-cracking also appears in standard tension tests in air.