Dynamic Thermomechanical Modeling of a Wet Shape Memory Alloy Actuator

Abstract

This paper presents combined thermal and mechanical models of a wet shape memory alloy (SMA) wire actuator. The actuator consists of a SMA wire suspended concentrically in a compliant tube. Actuation occurs as hot and cold water that are alternately pumped through the tube to contract and extend the wire, respectively. The thermomechanical model presented in this paper accounts for the nonuniform temperature change of the SMA wire due to alternating the temperature of the flow along the wire. The thermal portion of the model consists of analysis of the heat transfer between the fluid and the SMA wire. Heat loss to the environment and the temperature change of the fluid through the actuator are taken into account. Based on this analysis, the temperature of the wire at segments along its length can be determined as a function of time. The mechanical portion of the model approximates the strain-martensite fraction and martensite fraction-temperature relationships. By combining the thermal and mechanical models, the displacement of the wire can be determined as a function of time. The combined thermomechanical model will be useful for predicting the performance of wet SMA actuators in a variety of applications.

Design of Shape Memory Alloy-Based Soft Wearable Robot for Assisting Wrist Motion

“…Typical type of SMA for actuator applications is in the form of wires [47][48][49][50]. The advantage of the wire-shaped SMA actuator is that it can produce high forces compared to the other soft actuator technologies such as Ionic Polymer Metal Composites [51], dielectric elastomers [52], shape-morphing polymers [53] and hydrogels [54].…”

“…Generally, many SMA-based actuators are operated in ambient air, which offers a fast heating rate, but the limitation is a slow cooling rate as well [46][47][48][49]59]. To enhance the response speed of SMA based actuators, a few works have applied water as an alternative coolant during the actuation of the SMA [50,[55][56][57][58]. Park et al developed SMA coil spring-based actuator that was composed of the SMA coil spring bundles and a stretchable polymer tube that can stretch over 300% of its initial length [55][56][57].…”

Modeling and characterization of shape memory alloy springs with water cooling strategy in a neurosurgical robot

“…The wet SMA actuator introduced by Ertel and Mascaro (Ertel and Mascaro, 2010) was an SMA wire placed in a compliant tube that changed its longitudinal shape with the SMA when it was heated by flowing hot water through the tube (Ertel and Mascaro, 2010). Cold water was then passed through the tube to cool the SMA wire.…”

“…Several SMA cooling methods such as fan cooling (Lewis et al, 2013), water-jet cooling (Zhang et al, 2008), mobile heat sink (Russell and Gorbet, 1995), Peltier effect (Luo et al, 2000; Selden et al, 2004) and wet actuator (Ertel and Mascaro, 2010) have been proposed in the literature. The water-jet cooling of a moving SMA was investigated to explore its potential use in the field of microelectromechanical system (MEMS) and it was found that the shape deformation of the actuator increases with increased jet speed and decreases with increased nozzle-to-surface distance (Zhang et al, 2008).…”

“…A mobile heat sink with an innovative friction clutch mechanism was developed without an increase in energy loss or power consumption (Russell and Gorbet, 1995). Media such as compressed air (Kim et al, 2014), thermal grease (Loh et al., 2006; Pathak et al, 2008) and water (Ertel and Mascaro, 2010; Pathak et al, 2008) have also been used for various research involving SMA wires and springs. However, a compact design that integrates the cooling mechanism with the SMA is still not available.…”