Pullout behavior of superelastic SMA fibers with various end-shapes embedded in cement mortar

This study investigated the effects of superelastic shape memory alloy (SMA) fibers end-shape on pullout resistance through hysteretic pullout testing. Superelastic NiTi SMA wire of 1.0 mm diameter was employed in manufacturing short fibers. SMAs were fabricated with four end-shapes: 1) prismatic and straight end, 2) L-shaped end, 3) N-shaped end, and 4) crimped end with a spearhead. The embedded length of a fiber into the mortar matrix having compressive strength of 50.0 MPa was 18.0 mm, except for the N-shaped end fiber for which the embedded length was 21.0 mm. The pullout test was conducted with displacement control to obtain hysteretic pullout behavior by four cycling loadings. The results showed that crimped-end fibers considerably magnified the pullout strength, and the deformation was recovered by their superelastic behavior. As N-shaped end fibers could not show flag-shaped behavior, another test was performed through which fibers were annealed to induce superelasticity, so, a perfect strain recovery was obtained. Results showed that additional annealing of the N-shaped fibers after the manufacturing improved superelastic behavior at the bended part.