Fabrication and modeling of shape memory alloy springs

Abstract

In this paper, shape memory alloy (SMA) helical springs are produced by shape setting two sets of NiTi (Ti-55.87 at% Ni) wires, one of which showing shape memory effect and another one showing pseudoelasticity at the ambient temperature. Different pitches as well as annealing temperatures are tried to investigate the effect of such parameters on the thermomechanical characteristics of the fabricated springs. Phase transformation temperatures of the products are measured by differential scanning calorimetry and are compared with those of the original wires. Compression tests are also carried out, and stiffness of each spring is determined. The desired pitches are so that a group of springs experiences phase transition during loading while the other does not. The former shows a varying stiffness upon the application of compression, but the latter acts as passive springs with a predetermined stiffness. Based on the von-Mises effective stress and strain, an enhanced one-dimensional constitutive model is further proposed to describe the shear stress-strain response within the coils of an SMA spring. The theoretically predicted force-displacement responses of the produced springs are shown to be in a reasonable agreement with the experimental results. Finally, effects of variations in geometric parameters on the axial force-displacement response of an SMA spring are investigated.

Thermomechanical Characterization of Superelastic Ni-Ti SMA Helical Extension Springs Manufactured by Investment Casting

“…Ni-Ti SMA springs are manufactured by "shape setting", wherein the wire is wrapped and fixed around a cylinder and then heat treated to obtain the coil spring shape. However, while usual and simple, this process depends on the preliminary fabrication of the Ni-Ti wires 4,14,15 . Thus, it is also important to develop processes for obtaining these components in a single manufacturing step, especially for custom applications.…”

Metallic alloy with shape memory – selected properties and engineering aspects

“…straight elements, products in the form of springs or other profiles). The aforementioned information is the reason behind the implementation of annealing treatment, which applicable temperature range varies between 300 and 600ºC, at adequate time intervals (suzuKi 1998, liu et al 2008, rao et al 2015, stortiero 2015, HaberlanD, elaHimia 2016, HeiDari et al 2016. The use of higher temperatures, during the heat treatment, is reported by Jahanbazi asl et al (2019).…”

“…There are not many literature positions currently available, especially in the category of complete engineering technological information about the above-mentioned steps. A contribution to a different extent in this field was made by some researchers (suzuKi 1998, liu et al 2008, rao et al 2015, heidari et al 2016, Jahanbazi asl et al 2019. Because SMM are still classified as engineering materials with high innovation potential, the authors of this work imply that this sort of insightful data can be useful for machine designers, various examples of mechanism employing SMA in fields such as mechanics, mechatronics and robotics, as well as for students or enthusiasts.…”

Modeling of torsion fatigue in shape memory alloys

“…Based on the approach proposed by Heidari et al (2016), by neglecting the thermal strain portion, it is assumed that the shear strain (g) consists of elastic and transformation-induced strains indicated by superscripts ''e'' and ''tr,'' respectively, that is…”