Grain size effects on stability of nonlinear vibration with nanocrystalline NiTi shape memory alloy

Abstract

Grain size effects on stability of thermomechanical responses for a nonlinear torsional vibration system with nanocrystalline superelastic NiTi bar are investigated in the frequency and amplitude domains. NiTi bars with average grain size from 10 nm to 100 nm are fabricated through coldrolling and subsequent annealing. Thermomechanical responses of the NiTi bar as a softening nonlinear damping spring in the torsional vibration system are obtained by synchronised acquisition of rotational angle and temperature under external sinusoidal excitation. It is shown that nonlinearity and damping capacity of the NiTi bar decrease as average grain size of the material is reduced below 100 nm. Therefore jump phenomena of thermomechanical responses become less significant or even vanish and the vibration system becomes more stable. The work in this paper provides a solid experimental base for manipulating the undesired jump phenomena of thermomechanical responses and stabilising the mechanical vibration system through grain refinement of NiTi SMA.

Analytical solution of a mass-spring system containing shape memory alloys: Effects of nonlinearity and hysteresis

“…To validate our model and analytical solutions, we simulate the experiments in Refs. [27,28] where a SMA torsional vibration system was built and the vibration responses were measured. The SMA wires used are of di erent grain sizes (in average) and their torsional behaviors are consequently di erent (Fig.…”

“…Moumni et al [24,25] employed coupled thermomechanical Zaki-Moumni model [7] to simulate the forced oscillation of an SMA mass-spring-damper system. Xia and Sun [26,27] investigated the jump phenomena of thermomechanical responses in the frequency, amplitude, and time domains for a torsional system with an NiTi wire and further explored the grain size e ect of NiTi polycrystals [28] on the stability of nonlinear dynamic responses. Jose et al [29] examined an SMA bar as a vibration isolator and evaluated the displacement transmissibility by numerically solving state space equations.…”

On the Fatigue Behavior of Nanocrystalline NiTi Shape Memory Alloys: A Review

“…Nc also known as medical-grade NiTi SMAs generally have average grain sizes below 100 nm, while coarse-grained counterparts have typically an average grain size of 10-100 µm [24][25][26]. Apart from the direct difference in grain size, the key distinction between nc and coarsegrained NiTi SMAs can be summarized as follows [27,28] (a) the density of the amorphous phase and grain boundary are higher in nc NiTi SMAs, and (b) due to the aforementioned fact the nc NiTi SMAs have number of special qualities including slower heat accumulation in cyclic loading which improves the cyclic stability and the strain recovery rate of the SMAs. Furthermore, nc NiTi SMAs exhibit a broader temperature window for superelasticity and a decrease in deformation rate sensitivity while maintaining good strain recoverability.…”

“…Recrystallization by heat treatments i.e. annealing needs to succeed one of the following techniques of SPD: high pressure torsion (HPT), cold-rolling, cold-drawing, local canning compression, surface mechanical attrition treatment (SMAT), equal channel angular pressing (ECAP), or accumulative roll bonding (ARB) [27][28][29][30][31][32][33]. ECAP of NiTi SMA per se can be utilized to increase yield stress and enhance crack growth resistance [34].…”

“…To date, numerous papers have studied fatigue in NiTi SMAs, but only a handful of them dealt with fatigue in nc NiTi SMAs [22,25,28,31]. Moreover, and to the best of authors' knowledge, none of the previous research provided a review of studies on fatigue in nc Nitinol.…”