New SMA Short Fibers for Cement Composites Manufactured by Cold Drawing

Abstract

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.

Optimizing Superelastic Shape Memory Alloy Fibers (SMAF) for Enhancing Pullout Performance in Engineered Cementitious Composites (ECC)

“…The The force-displacement curves of Linear, indented, and hooked SMAF with 0.8 diameter in ECC-2 mix, along with these three fibers subjected to abrasive surface treatment, are presented in Figure 10. Three factors contribute to the bonding stress inside a fiber: chemical adhesion, frictional resistance, and anchoring action [48]. With their cross-section, LS-SMAF showed poor anchoring performance.…”