This work reexamines traditional shape memory alloy (SMA) loading paths commonly used in SMA-based actuator applications and presents a novel, superimposed condition in which SMA generates substantial forces upon heating and cooling. This atypical effect, which is investigated with a textile-based actuator, was found to be prominent at the completion of material phase transformation, at which point thermal expansion/contraction became the dominant force-generating mechanism. We demonstrate that amplification of generated forces can be accomplished by varying the applied thermal load, applied structural strain, as well as actuator architecture. Specifically, we present SMA knitted actuators as an actuator architecture that increases the effect by aggregating SMA wires within a complex strain profile - effectively providing a larger operational window for the effect to propagate. The amplification of blocking forces through this novel operational procedure suggests reconsidering traditional blocking force design paradigms and opens untapped actuator application spaces, such as the highlighted medical and aerospace wearable technologies.
Bibliographical noteFunding Information:
This work was supported in part by a NASA Space Technology Research Fellowship (Grant #80NSSC17K0158), Minnesota’s Discovery, Research, and InnoVation Economy Robotics, Sensors, and Advanced Manufacturing (MnDRIVE RSAM) Initiative, and the University of Minnesota Office of the Vice President for Research UMII MnDRIVE Graduate Assistantship. Thank you to Kirstyn Johnson from NASA Johnson Space Center’s Crew Survival Lab as well as Amy Ross and Shane McFarland from the Advanced Spacesuit Lab for guidance on the astronaut compression garment concept and operation. Thank you for support from the University of Minnesota’s Wearable Technology Lab, specifically Heidi Woelfe, for coordinating time on the Instron machine. The authors thank Othmane Benafan and Santo Padula II from NASA Glenn Research Center for discussions related to the SMA material effects that may contribute to the behaviors described in this publication.
- blocking force
- knitted actuator
- shape memory alloy
- thermal expansion