A Comparative Study of Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 Tube Actuators

Abstract

A shape memory alloy (SMA) actuator typically has to operate for a large number of thermomechanical cycles due to its application requirements. Therefore, it is necessary to understand the cyclic behavioral response of the SMA actuation material and the devices into which they are incorporated under extended cycling conditions. The present work is focused on the nature of the cyclic, evolutionary behavior of two widely used SMA actuator material systems: (1) a commercially available Ni 49.9 Ti 50.1 , and (2) a developmental high-temperature Ni 50.3 Ti 29.7 Hf 20 alloy. Using a recently developed general SMA modeling framework that utilizes multiple inelastic mechanisms, differences and similarities between the two classes of materials are studied, accounting for extended number of thermal cycles under a constant applied tensile/compressive force and under constant applied torque loading. From the detailed results of the simulations, there were significant qualitative differences in the evolution of deformation responses for the two different materials. In particular, the Ni 49.9 Ti 50.1 tube showed significant evolution of the deformation response, whereas the Ni 50.3 Ti 29.7 Hf 20 tube stabilized quickly. Moreover, there were significant differences in the tension-compression-shear asymmetry properties in the two materials. More specifically, the Ni 50.3-Ti 29.7 Hf 20 tube exhibited much higher asymmetry effects, especially at low stress levels, compared to the Ni 49.9 Ti 50.1 . For both SMA tubes, the evolution of the deformation response under thermal cycling typically exhibited regions of initial transients, and subsequent evolution.

Detwinning of preloaded martensite in shape memory alloys and its effect on the cyclic behavior of NiTi cylindrical actuators

“…Also, for the Ni 50.3 Ti 29.7 Hf 20 alloy, which did not indicate any visible demarcations along the stress versus strain response curve (see marked points “o”–“i”–“ii” in Figure 4), the actuators demonstrated similar qualitative thermomechanical response character, that is, being nearly dimensionally stable even under shear stresses greater in magnitude than the originally investigated stress of 400 MPa in Owusu-Danquah et al (2015). This is evident in the negligible amount of the accumulated open-loop angle of twists stated in Table 5 for the NiTiHf actuators.…”

“…The SMA model is parameterized to capture the cyclic responses of a ternary aged-Ni 50.3 Ti 29.7 Hf 20 (Bigelow et al, 2011) and a binary Ni 49.9 Ti 50.1 (Padula et al, 2012, 2014) actuation materials. An attempt is made herein, to address some of the factors that could lead to the unusual experimental observation made for the Ni 49.9 Ti 50.1 samples, as well as provide complementary results to the initial outcome of our previous comparative study (Owusu-Danquah et al, 2015) regarding SMA tubular actuators.…”

“…This provides the primary motivation for the present study. Moreover, in our previous comparative study (Owusu-Danquah et al, 2015), it was observed that under limited stresses of 150 MPa in Ni 49.9 Ti 50.1 and 400 MPa in Ni 50.3 Ti 29.7 Hf 20 , higher linear and torsional actuation strokes were generated by the Ni 49.9 Ti 50.1 cylindrical tubular actuators relative to the Ni 50.3 Ti 29.7 Hf 20 counterpart (of the same configuration), for three uniaxial loading cases of tension, compression , and torsion . On the other hand, the Ni 50.3 Ti 29.7 Hf 20 actuator showed a dimensionally stable response character (Benafan et al, 2014a; Evirgen et al, 2015) for all the loading conditions used in that study.…”

“…The parameters used for the model calibration are similar to that implemented in Owusu-Danquah et al (2015) for the two SMA systems. The values for these material parameters were carefully chosen based on the different sets of experimental test data showing the respective cyclic, nonlinear deformation responses of these alloys.…”

“…The parameters stated in Table 3 were also used for the Ni 49.9 Ti 50.1 material. Sample comparative results showing the model’s capability in predicting the distinct responses of these two alloys can be found in Owusu-Danquah et al (2015) and Saleeb et al (2015). Moreover, guided by isolated test data (in existing literature), deductions were made for the model parameterization to account for the cyclic response of the Ni 49.9 Ti 50.1 alloy under higher stress magnitudes, that is, between 300 and 500 MPa.…”