Modeling and Experimental Validation of Shape Memory Alloy Bending Actuators

In this paper, we develop a computational model that can be used to investigate and optimize the performance of shape memory alloy (SMA) bending actuators. These actuators (approximately 7–21 mm in length) consist of curved SMA wires embedded within elastic sleeves and are intended for positioning and anchoring robotic catheters inside blood vessels during clinical treatments. Each SMA wire is shape-set to an initial curvature and inserted along the neutral axis of a straight elastic member (cast heat-resistant silicone with varying section modulus). The elastic member preloads the SMA (or produces a stress-induced phase transformation), reducing the equilibrium curvature of the composite actuator. Temperature-induced phase transformations in the SMA (via Joule heating) enable strain recovery and increased bending (increased curvature) in the composite actuator. The homogenized energy framework is utilized to model the behavior of this composite actuator, and the effects of several critical design parameters (initial SMA curvature and section modulus of the elastic member) on the deactivated and activated curvatures are investigated. Experimental results validate the model, enabling its use as a design tool for bending performance optimization.