Prestressing technique with recovery stress of cold-drawn superelastic SMA cables

This study investigates inducing of recovery stress of cold-drawn superelastic shape memory alloy (SMA) wires. It is well known that the cold-drawn martenstic SMA wires show recovery stress, which can be used for prestressing in cementitious materials. The cold drawing work introduces tensile strain in the martensitic SMA wire as well as reduces the cross-sectional area. The heating transforms phase state of the cold-drawn martensitic SMA wire resulting in inducing recovery stress. This study tries the cold drawing work on a superelastic SMA wire and then obtains the recovery stress by heating. If the applied strain is on the stress-induced-hardening state, the phase is detwinned, whose deformation can be recovered by the phase transformation. Therefore, after the cold drawing work, it is conjectured that the superelastic SMA wire is transformed to the similar state of the cold-drawn martensitic SMA wire. The cold-drawn superelastic SMA wire shows a similar recovery stress to that of the cold-drawn martenstic SMA wire. Morevoer, it shows similar flag-shaped tensile behavior under the recovery stress; this indicates that the cold-drawn superelastic SMA wire provides more displacement recovery capacities than the corresponding one of the martensitic SMA wire. This is very meaningful to apply it on civil structures. Then, SMA cables made by the cold-drawn superelastic SMA wires are tested for inducing recovery stress. The SMA cables can be practically used for prestressing on concrete members.