Behavior of NiTiNb SMA wires under recovery stress or prestressing

Abstract

The recovery stress of martensitic shape-memory alloy [SMA] wires can be used to confine concrete, and the confining effectiveness of the SMA wires was previously proved through experimental tests. However, the behavior of SMA wires under recovery stress has not been seriously investigated. Thus, this study conducted a series of tests of NiTiNb martensitic SMA wires under recovery stress with varying degrees of prestrain on the wires and compared the behavior under recovery stress with that under prestressing of the wires. The remaining stress was reduced by the procedure of additional strain loading and unloading. More additional strains reduced more remaining stresses. When the SMA wires were heated up to the transformation temperature under prestress, the stress on the wires increased due to the state transformation. Furthermore, the stress decreased with a decreasing temperature of the wires down to room temperature. The stress of the NiTiNb wires was higher than the prestress, and the developed stress seemed to depend on the composition of the SMAs. When an additional strain was subsequently loaded and unloaded on the prestressed SMA wires, the remaining stress decreased. Finally, the remaining stress becomes zero when loading and unloading a specific large strain.

Iron-based shape memory alloy strips for strengthening RC members: Material behavior and characterization

“…In civil engineering applications, SMAs can be exploited for their superelasticity or SME properties for example NiTiNb alloys [10][11][12]. Some demonstration projects do exist in this context [1,[13][14][15][16][17][18].…”

Recovery stress of shape memory alloy wires induced by hydration heat of concrete in reinforced concrete beams

“…The developed recovery stress with the 3% prestrain is larger than the stress of 398 MPa, which corresponds to 3% strain in the SMA bar. The residual stress, which is the remaining stress after cooling to air temperature, is generally smaller than the stress of 398 MPa, as previous studies indicated (Choi et al, 2010a, 2012b). The prestress in the SMA bar due to the 5% strain is 444 MPa.…”

Thermo-mechanical characterisation of NiTi-based shape memory alloy wires for civil engineering applications

“…Suhail et al (2020b) showed that forward transformation temperatures follow a linear relationship with applied pre-strain that is, greater the applied pre-strain, greater in the shift in the forward transformation temperatures. Other studies (Choi et al, 2013;Li et al, 2003;Proft and Duerig, 1990) have shown that recovery stress not only depend on the chemical composition and transformation temperatures of an SMA but also only the level of pre-strain applied. Proft and Duerig (1990) showed that the recovery stress in NiTiFe (47%Ni, 50%Ti and 3%Fe (at.…”