<p>Shape memory alloys (SMAs) are attractive actuators due to their high strength and small form factor. When properly trained, SMAs shorten in length mimicking the motion of skeletal muscles. SMAs can be coupled with passive materials in order to convert their linear motion into larger bending motion. The deformation profile is then a function of SMA properties and actuator geometry. Traditional beam theories cannot accurately model the large deformations achieved by these beam actuators due to their large displacements. This work applies the Cosserat theory (also known as geometrically-exact beam theory) of beams to model the maximum deformation profile of an SMA embedded unimorph actuator. An experimental SMA unimorph actuator with a length of 101.3 mm was made with SMA wires routed along the length of a rectangular cross-sectional piece of spring steel. Reflective point tracking markers were adhered along the length of the actuator to track its profile during actuation. The SMA was heated until it reached maximum deformation, and the recorded motion was processed with machine vision. The experimental profile was then compared to the Cosserat theory deformation profile, which showed good agreement. The maximum displacement from the rest position was 33.4 mm and the average absolute (relative) error between the model prediction and experimental results was 0.98 mm (2.93%) with a peak absolute (relative) error of 1.3 mm (7.06%).</p>

Modeling Deformation of Unimorph Shape Memory Alloy Actuators Using Cosserat Theory

Paper Proceedings: https://asmedigitalcollection.asme.org/IDETC-CIE/IDETC-CIE2021/volume/85369

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