PSI - Issue 17

Mihaela Iordachescu et al. / Procedia Structural Integrity 17 (2019) 434–439 M. Iordachescu et al./ Structural Integrity Procedia 00 (2019) 000 – 000

435

2

bearing load capacity in tension (FIB bulletin 30, 2005). The International Federation for Structural Concrete (FIB) in the FIB bulletin 30 (2005) and recent standards (UNE-EN ISO 15630-3, 2010) recommend the deflected tensile test for the selection of strands and prestressing steel wires. However, this kind of testing is not quite appropriate to analyse the macro and micro failure mechanisms that transversal loading involves. Accordingly, the basic guidelines of the experimental approach firstly used and discussed by Maupetit P. et al. (1977) are followed in present research. The paper presents a comparative experimental analysis of the failure mechanisms induced by the combination of tensile and transverse compressive loads in high-strength cold drawn eutectoid and lean duplex stainless steel wires, the first currently used for strands manufacturing and the second, as a potential candidate for replacing it. Recent researches of Valiente A. and Iordachescu M. (2012), Iordachescu M. et al. (2015) and De Abreu M. et al. (2018) have shown the potential of cold-drawn stainless steel wires for being used in pre or post tensioned structural applications, not only due to their mechanical properties and pitting corrosion resistance, but also for the damage tolerance and stress corrosion resistance. The fracture tests under biaxial loading (T-QL) were carried out with a specially designed device that allowed applying and maintaining the local transverse compression load during the axial tensioning of wires. The transverse load was applied with a servo-hydraulic actuator whose replaceable plunging end is a small-length wire sample of same material and diameter as the tested one. The tests provided the combinations of tensile and transverse compression loads able to cause the wires rupture. On this basis, an empirical fracture criterion valid for both eutectoid and duplex steel wires was formulated, despite of the observed failure mechanisms differences. These were attributed to the microstructural features of each wire regarding the axial orientation induced by the cold drawing process.

Nomenclature A 0

wire cross-section

A h ES

contact area

high-strength eutectoid wire LDS high-strength lean duplex stainless steel wire P 0 tensile load in simple tension P m maximum tensile load under transverse loading Q transverse compression load T-QL tensile test under local transverse loading of wires δ percentage elongation

2. Materials and Testing Method

2.1. Materials characteristics

The studied materials are two 4 mm diameter, high-strength commercial wires made of eutectoid steel (ES) and lean duplex stainless steel (LDS), both manufactured by cold drawing which determines the strong microstructures anisotropy, elsewhere discussed by Iordachescu M. et al. (2015). Tables 1 and 2 respectively indicate the chemical composition and the mechanical properties at room temperature as obtained by tensile testing wire samples of 350 mm length. The maximum loads registered in the simple tensile test were further used as reference values for quantifying the effect of the transverse compression load on the tensile behavior of both wire classes, when subjected to biaxial loading.

Table 1. Chemical composition of studied wires (percentages by weight)

Acero

C

Si

Mn

P

S

N

Cr

Mo

Ni

Fe

LDS

0.03 0.78

1.00 0.21

5.00 0.67

0.035 0.015 0.012 0.022

0.11

20.50

0.60

2.25

Bal. Bal.

ES

-

-

-

-