Abstract
<p class="1Body">This study suggests new shape memory alloy reinforcing fibers manufactured by cold drawing method. This study prepares NiTi shape memory alloy (SMA) wires with diameter of 1.0 mm. Then, the wires are elongated by cold drawing and, thus, the diameters are reduced to 0.93 or 0.965 mm, respectively. This procedure introduces prestrain into the wires. When elongated SMA wires are heated, the shape memory effect is activated; this process recovers the deformed length as well as the reduced diameter due to Poisson’s effect. Cold drawn wires with diameters of 0.93 and 0.965 mm recover diameters of 0.018 and 0.024 mm, respectively, with heating. The bulging of the SMA fiber in the radial direction inside cement composites induces confining pressure around the fiber and increases bond strength. When an SMA fiber is heated at the both ends, the heated parts bulge and the fiber shape looks like a dog-bone. Such a dog-bone shaped fiber can provide a geometrical anchoring action that also increases the bond resistance of the fiber. This study conducts pullout tests of SMA fibers to understand their pullout behavior and assess bond stress. The heated fibers and dog-bone shaped fibers increase pullout force compared to those of as-received and cold-drawn fibers. When dog-bone shaped fibers are heated, they show twice the pullout force of dog-bone shaped fibers without heating because geometric anchoring action as well as additional frictional resistance due to confining pressure are activated.</p>
Highlights
Shape memory alloys (SMAs) are smart materials that have received high attention in aerospace, mechanical, and medical engineering fields
This study suggests new shape memory alloy reinforcing fibers manufactured by cold drawing method
shape memory alloy (SMA) wires have been widely used for various targets in civil engineering: such as confining or prestressing of concrete, seismic isolation devices, or reinforcing fibers of cement composites
Summary
Shape memory alloys (SMAs) are smart materials that have received high attention in aerospace, mechanical, and medical engineering fields. In the last two decades, applications of SMAs in civil engineering have increased year by year; these applications include seismic isolation (Dolce et al, 2000; Sharabash & Andrawes, 2010; Ozbulut & Hurlebaus, 2010; Choi et al, 2005) or retrofit devices (DesRoches & Delemont, 2002), energy dissipation devices (Yang et al, 2010), devices for the prestressing of concrete (Sawaguchi et al, 2006; Maji & Negret, 1998), and smart cement composites (Krstulovic-Opara & Naaman, 2000; Shajil et al, 2013). Superelasticity contributes to provide a self-centering capacity (Choi et al, 2010a) or self-healing of concrete (Song et al, 2006). For these purposes, several types of SMAs such as bars, cables, or wires have been used. SMA wires have been widely used for various targets in civil engineering: such as confining or prestressing of concrete, seismic isolation devices, or reinforcing fibers of cement composites
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