Modeling of torsion fatigue in shape memory alloys

Abstract

Fatigue in shape memory alloys is one of the crucial aspects of their behavior; however, the current knowledge is mainly focused on uniaxial fatigue and is inadequate for engineering purposes. In this article, a fatigue criterion based on the stabilized dissipated energy has been presented to investigate the torsional low-cycle fatigue of superelastic shape memory alloys. To this aim, a one-dimensional torsional constitutive model in addition to a modified fully coupled thermomechanical model has been utilized so that the torsional cyclic responses especially in relatively high loading frequencies, which contribute to remarkable temperature variations and consequent response changes, could be taken into account. The calculated stabilized dissipated energy, then, has been used in an energy approach fatigue criterion in order to predict the fatigue life; hence, an explicit relation, which is capable of determining the number of cycles to failure for different loading conditions at a given loading frequency, has been obtained. The numerical results have been appraised for NiTi specimens, and they have been shown to be in a good agreement with the experimental data. Finally, using the proposed approach, the effect of fatigue test parameters on the fatigue life has been studied.

The role of NiTi shape memory alloys in quality of life improvement through medical advancements: A comprehensive review

“…Numerous models have been developed to describe and predict the functional characteristics of SMAs by researchers such as Auricchio et al, 68 Gu et al, 69 Liu et al, 70 and many more. [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89]…”

Defect mitigation and structural control of cantilevered structures using shape memory wire based resonant stiffness sensing

“…32 Other attributes like, operating at a lower frequency and activating the SMA well below the maximum operating point increase the fatigue life to an extent. 33 The testing technique is conducted such that the SMA is activated below the operating point, that is, the SMA wire is activated at 210 mA, while the safe heating current is 320 mA. The laser displacement sensor detects the change in the stiffness of the beam, and the processor continuously records, stores, and displays the new resonant condition corresponding to each new measurement, the stiffness of the structural element (beam), and a measure of the measurand.…”

“…of stabilized cycles whereas the stiffness of copper based SMAs decays with time which decreases their fatigue life 32 . Other attributes like, operating at a lower frequency and activating the SMA well below the maximum operating point increase the fatigue life to an extent 33 . The testing technique is conducted such that the SMA is activated below the operating point, that is, the SMA wire is activated at 210 mA, while the safe heating current is 320 mA.…”

Duo features of shape memory wire for resonant force sensing

“…The construction of the sensing mechanism (SMA wire with deadweight suspended to the fundamental component, the beam) is such that its natural frequency is reduced by three times that of the fundamental element, the beam. Reduced frequency of operation and activation of the SMA far below the maximum operating point extend fatigue life to some extent [28]. The reduction in the frequency also causes greater amplitude of oscillations thereby increases the sensitivity of the system which is desirable of any sensing mechanism.…”