Pseudoelastic fatigue of NiTi wires: frequency and size effects on damping capacity

Abstract

The damping properties associated with hysteretic behavior of the pseudoelastic stress-strain (σ -ε) curves of NiTi shape memory alloy (SMA) wires were studied. Damping was characterized for wires of 2.46 and 0.5 mm diameter using samples of 120 mm in length. The effect of the frequency and size of the wire on the σ -ε curves were studied in the 3 × 10 −5 -3 Hz range, with 8% maximal strain. Damping associated parameters, such as hysteresis width, dissipated energy and specific damping capacity (SDC), defined as the ratio between the hysteretic energy and the maximum strain work over a complete pseudoelastic cycle, show maximum values at a specific frequency for each size diameter. These findings were explained in terms of the temperature effects associated to the heat of transformation. Results show that NiTi wire of 0.5 mm diameter has the highest SDC when cycling around 0.1 Hz while wire of 2.46 mm diameter has the highest SDC at 0.01 Hz. At 1 Hz, the SDC for 0.5 mm diameter wire is around twice that of 2.46 mm diameter wire.

Shape memory alloys as an effective tool to damp oscillations

“…The results for the two sets showed similar approximately Gaussian behavior, with a maximum at 0.01 Hz. Analysis for the thin wires showed that the frequency of the maxima increased with the decrease in the wire diameter [108]. In practical damping applications, the working frequencies start near 1 Hz and the value is a function of the structure.…”

“…15. The plot of the hysteresis versus the frequency exhibits a ''symmetric'' shape [108,109] that is associated with the maximal deformation of 8 %. The A and B points were determined for the initial and the final cycles in the first set of measurements (dots).…”

“…The fan effect may be related to compensatory amounts of released and absorbed latent heat in the ''fan off'' (free convection) cycles compared to the ''fan on'' (forced convection) cycles and to pseudo-adiabatic behavior. Soul et al [108] showed wider hysteresis when latent heat was released to the surroundings before the start of retransformation compared to a more adiabatic cycle. In the first series of ''fan on'' (forced convection) cycles, the partially localized transformation resulted in self-heating and required more stress because the wire was under room temperature from the previous cycle, but less cold than when there is only free convection.…”

Cyclic pseudoelastic behavior and energy dissipation in as-cast Cu-Zn-Al foams of different densities

“…In general, at low frequency levels, effects on the SDC in shape memory alloys are associated to the dissipation of heat generated by the samples. For example, this is a well known effect in Ni-Ti where a combination of high transformation enthalpy and relatively low thermal conduction results in a strong frequency dependent behavior [27,29]. In the case of Cu-Zn-Al foams, the heat is efficiently removed by the material high thermal conduction, enhanced by the particular open morphology of the foam itself.…”

An innovative approach to achieve re-centering and ductility of cement mortar beams through randomly distributed pseudo-elastic shape memory alloy fibers

“…They did experiments with prestrained and unprestrained SMA wires in FRP composite beams. Use of PESMA as rebars in concrete structures in seismic areas was found to be effective in achieving the recentering capability (Soul et al, 2010). While considering the economic aspects, it is better to use PESMA bars at the beam-column joint alone or in the plastic hinge zones by providing proper connection between bars of PESMA and steel.…”