Damping and Re-Centering Capabilities of Superelastic NiTi Wires: Evaluation of an In-scale Device for Structural Control

Superelastic effect is being considered for passive control of civil and mechanical structures subjeted to dynamic loads. While damping capacities provided by the hysteretic behavior of superelastic SMAs are comparable to high‑damping materials (elastomers, yielding metals), their advantages reside in the particular features associated with superelasticity. On the one hand the drop in effective stiffness during transformation limits load transfer to the structure and, on the other hand, the retransformation plateau supplies a restoring force up to almost zero strain. The latter represents a significant advantage of SMAs; indeed modern codes have introduced rules for re-centering capacity in seismic isolation.

In this work, a device which exploits both the dissipative and the recentering capabilities of superelastic NiTi wires is characterized. It is shown that, by mean of applying different pre-strain levels the cycling residual strain can be compensated, avoiding the necessity of a time‑costly pre‑cycling procedure. The performance of an in-scale damping device composed of two wires of 1.2 mm diameter was experimentally studied, at amplitudes up to 5 mm and for frequencies in the range 1E-3 -5 Hz. It was found that the dissipated energies follow non‑monotonic dependence with frequency reaching maximum values for intermediate values.