PSI - Issue 17

Maricely De Abreu et al. / Procedia Structural Integrity 17 (2019) 618–623 M. De Abreu et al./ Structural Integrity Procedia 00 (2019) 000 – 000

620

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Fig. 1. The samples, of 350 mm length, were gripped on the frame of the servo-hydraulic testing machine with commercial wire-wedges by means of which they were cyclically tensile loaded in the longitudinal direction. At once, the static transverse compression load was perpendicularly applied to the wire axis by using a small independent loading cell. This was designed to secure the transverse loading of the wire sample without parasite axial loading (Fig. 1a) induced by sliding friction between the wire sample and the actuator and the supporting plate of the small cell. This condition is achieved through the pulley counterweight system, which hangs from the testing machine and balances the frame weight. The actuator is pushed by an oil-hydraulic mini-cylinder fed by an air-oil pressure multiplier and a compressed air-bottle, whose pressure-regulator allows a fine enough manual control of the transverse load. The mini-cylinder piston of 30 mm diameter compresses the tested wire with the active force that receives from the oil-pressure. This is transmitted to the tested wire by means of a small piece of the same wire, which acts as a transversal actuator. This wire-actuator remains lodged in a V-shape die while applying the transverse load to the tested wire, whose backside is longitudinally supported on a V-grooved plate that receives the corresponding reaction force (Fig. 1b). Figs. 1c, 1d-1 and 1d-2 show details of the wire sample during testing, just before being transversely loaded, and just after failure.

Table 1. Mechanical properties of studied wires

Area Reduction [%]

Yield strength [MPa]

Tensile strength [MPa]

Maximum uniform deformation [%]

Mechanical properties Elastic modulus [GPa]

LDS

180 205

1350 1640

1820 1740

2.3 3.2

51 50

ES

Fig. 1. a) General view of the fatigue tensile test with transverse load (F-QL); b) Sketch of the biaxial loading; Details of the transverse loading: c) during testing; d-1) before transverse loading; d-2) at failure.

For prestressing strands wires free from transverse loading the fatigue lives higher than 2 ∙ 10 6 load cycles within the stress range of 200 MPa are considered unlimited by FIB (FIB, 2005). Accordingly, all F-QL tests were carried out in this stress range, at 12 Hz frequency, under different combinations of maximum fatigue load and transverse load, P max -Q. The tests were interrupted at 2 ∙ 10 6 load cycles, and in some cases at 5 ∙ 10 6 cycles. After the test, the wires that did not failed were loaded in simple tension until rupture to determine their remaining tensile capacity.