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

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Table 2. Mechanical properties of studied wires

Yield strength [MPa]

Tensile strength [MPa]

Maximum uniform deformation [%]

Mechanical properties Elastic modulus [GPa]

Elongation [%]

LDS

180 205

1350 1640

1820 1740

2.3 3.2

51 50

ES

2.2. Testing method

The purpose of the designed biaxial test type, which combines the axial tensile loading of the wires with a locally applied transverse loading (T-QL) was to evaluate the sensitivity of their tensile bearing capacity to the transverse loads which occur due to the contact in between them or with other structural components when incorporated into multi-wire strands for prestressing applications. As shown in Figs. 1a and 1b, the actuator that applies the transverse load is a small wire sample of the same material as the tested one. This actuator receives the plunging force along a groove made in the supporting plate perpendicularly to the tensioning direction. The arrangement assures an almost circular imprint generated in the two wires by plastic deformation once the transverse load is applied, because of the 90 0 symmetry of the contact (Fig. 1.c).

Fig. 1. a) General view of the tensile test with local transverse load (T-QL); b, c) Sketches of the biaxial loading of wires; d) Images showing the main testing phases: initial (no loading), intermediate (axial and transverse loading), and final (failure); e, f) Transverse load effect on the tensile-elongation curves of ES and LDS wires. Figs. 1e and 1f show the load-elongation curves obtained from the T-QL tests of lean duplex steel (LDS) and eutectoid steel (ES) wires, for distinct values of transverse load, Q. The elongation data were obtained by using the video extensometry technique applied on the sequence of images acquired during the test, on a gauge length of 12.5 mm, centered on the transverse load line. As shown by the plots given in Figs. 1e and 1f, the tensile bearing capacity of all T-QL tested ES and LDS wires markedly decreases with the transverse load. This reduction is accompanied by a slight increase of ductility. The last is a consequence of the extended plastic instability preceding the ultimate failure of the tested wires. In addition to mechanical testing, scanning electron microscopy (SEM) technique was used to determine the damage micromechanisms in both ES and LDS wires. In this view, both the fracture surfaces of the specimens and the contact areas generated by the transverse load were examined. To get more insights in the generated damage, axial and transverse metallographic samples were prepared and SEM analyzed from some of the fractured wires and