Unraveling Frequency Effects in Shape Memory Alloys: NiTi and FeMnAlNi

Abstract

With the presence of internal interfaces such as the austenite-martensite interface and the internal twin boundaries in the martensite, shape memory alloys (SMAs) can be employed in passive/active damping applications. Due to the latent heat of transformation, a temperature rise/drop during a load/unload cycle is expected to dynamically couple with the mechanical response of the SMA and influence the stress levels of forward/reverse transformation and thus the hysteretic area (i.e. the dissipated energy). Additionally, the temperature change per cycle is a function of loading frequency due to momentary heat transfer effects. To this end, for the first time, we demonstrate a rate insensitive shape memory alloy system, Fe 43.5 Mn 34 Al 15 Ni 7.5 which also exhibits near-zero temperature dependent stress-strain response. Contrastingly, we show that Ni 50.8 Ti, which is widely used commercially, is highly rate sensitive. With straightforward in situ experiments, complemented with thermomechanical modelling, we pinpoint the key material parameter which dictates frequency sensitivity. The corresponding results are then discussed in the light of different mechanisms contributing to the damping capacity of SMAs.

A Review Article on FeMnAlNi Shape Memory Alloy

“…Shape recover rate can be increased by increasing the aging period also about the thermomechanical processing of the alloy. From frequency effect it ensures that this alloy is having zero temperature dependence and high damping capacity (19). Ability to withstand the transformation stress level up to 500-600MPa (22).…”

“…Due to low change in temperature during loading FeMnAlNi alloy shows rate insensitive stress-strain response whereas in NiTi alloy shows high rate sensitive because of its large change in temperature. FeMnAlNi alloy is one of best alloy to be used under damping application because of its zero-temperature dependence, rate insensitive behaviour and high specific damping capacity (19,20,21).…”

Relevant Choices Affecting the Fatigue Analysis of Ni-Ti Endovascular Devices

“…However, a heating effect associated with the latent heat generated during phase transformation is well-recognized in air that can ultimately affect the characteristic stress-strain response of the material with a strong influence on the testing frequency [40][41][42]. It is well-established that at quasi-static strain rates, comparable to those at which static material characterization is performed (below 10 −4 s −1 ), the latent heat generated during stress-induced martensitic transformation can be timely exchanged with the surrounding environment without any increase in the temperature of the specimen, leading to a characteristic flag-shaped stress-strain curve [43,44] (Figure 4a). As the loading rate increases from 10 −4 s −1 to 10 −3 s −1 , the available time for latent heat convection decreases, causing a slight increase in the temperature of the specimen during loading and a decrease during unloading [39,40,42,44].…”

“…It is well-established that at quasi-static strain rates, comparable to those at which static material characterization is performed (below 10 −4 s −1 ), the latent heat generated during stress-induced martensitic transformation can be timely exchanged with the surrounding environment without any increase in the temperature of the specimen, leading to a characteristic flag-shaped stress-strain curve [43,44] (Figure 4a). As the loading rate increases from 10 −4 s −1 to 10 −3 s −1 , the available time for latent heat convection decreases, causing a slight increase in the temperature of the specimen during loading and a decrease during unloading [39,40,42,44]. Given the well-known Clausius-Clapeyron relation, establishing a linear relationship between the temperature and the transformation stresses [45], this heating effect determines a slightly higher forward transformation stress and a reduced reverse transformation stress, as is visible in Figure 4a.…”

“…By further increasing the loading frequency up to high strain rates (above 10 −3 s −1 ), the temperature of the sample drastically changes during the phase transformation as the latent heat cannot be convected timely. Heat accumulation inside the material causes a hardening effect with a progressive increase in the slope of the stress plateaus [40][41][42]; moreover, as heating provides a driving force for transformation during unloading, reverse transformation from martensite to austenite occurs at higher stresses, and the hysteresis loop narrows [44]. According to a recent work by Sidharth et al [44] investigating the damping capacity of differently oriented Ni-Ti single crystals in a wide frequency range between 0.01 Hz and 10 Hz, a stabilization of these effects seems expected, even if data regarding common testing frequencies for stent durability have not been provided.…”