PSI - Issue 28

Jesús Toribio et al. / Procedia Structural Integrity 28 (2020) 2386–2389 Jesús Toribio et al. / Procedia Structural Integrity 00 (2020) 000–000

2387

2

Particularly, prestressing steel wires are highly susceptible to hydrogen embrittlement, HE (Lillard et al. , 2000; Perrin et al. , 2010; Toribio et al. , 2011). Thus, a reduction of the residual stress state leads to a decrease of the HE susceptibility, lowering the risk of failure. In this paper, the effects of diverse cyclic loading scenarios on the residual stress field generated by cold drawing are analyzed. To achieve this goal, two finite element (FE) simulations were carried out: on one hand, a simulation of a wire drawing chain for obtaining the manufacturing-induced residual stress in a commercial prestressing steel and, on the other hand, a simulation of fatigue loading for revealing the effects of cyclic loading on the stress 2. Numerical modeling To compute residual stresses, a numerical simulation of a real drawing process was carried out by using a commercial finite element (FE) code. During this manufacture process the wire section is progressively reduced, from an initial diameter ( d 0 ) of 12 mm (associated with the hot rolled bar) to a final diameter ( d 6 ) of 7 mm (corresponding to the prestressing steel wire) after six drawing steps. Elastoplastic analysis was performed in both simulations using large deformations and large strains with updated Lagrangian formulation. Experimental tensile tests up to fracture were carried out to obtain the stress–strain curves of both materials (Fig. 1): the hot rolled bar (FE simulation of wire drawing) and the cold-drawn prestressing steel wire (FE simulation of fatigue loading).

2000

1500

1000

 (MPa)

500

Prestressing steel wire Hot rolled bar

0

0

0.02 0.04 0.06 0.08



Fig. 1. Master stress vs. strain curves of a hot rolled bar and a prestressing steel wire.

The FE simulation of wire drawing reveals the residual stress state that will be used later as an input in the numerical simulation considering both states: the residual one and that caused by in-service loading (fatigue loading). According to the results shown in Fig. 2, the wire at the end of the process exhibits a non-uniform radial distribution of axial stress, with tensile stress near the surface and compressive one in the core. Regarding the numerical modelling of the in-service loading, including the previously computed residual stress state, three different cyclic loading schemes were studied (Table 1) with a sinusoidal shape variation and a stress factor R =  min /  max = 0. The values of both (i) the maximum stress in absolute value (  max ), and (ii) the maximum stress normalized with material yield strength (  =  max /  Y ), are included in Table 1 for the cyclic loadings considered in the analysis.