Design, prototyping and computer simulations of a novel large bending actuator made with a shape memory alloy contractile wire

Abstract

A novel design for a large bending actuator is presented for the first time. It is composed of three components: an inner flexible beam or strip, a nickel - titanium shape memory alloy (SMA) contractile wire, and an outer soft plastic tube. The SMA wire is embedded between the beam and the plastic tube, and connected to the beam only at both ends of the beam. With this structure, a small change in the strain of the SMA wire results in a large bending deformation of the beam. To predict the behavior of the actuator, a mathematical model and a numerical simulation approach are then developed. The Brinson model for SMAs with constant material functions is used for modeling of the SMA wire component. The model of the actuator structure is associated with geometric nonlinearity of the large deflection beam and hysteretic nonlinearity of the SMA wire. A Galerkin finite-element formulation and an iterative procedure are used in the development of the numerical approach. A prototype of the actuator is made. Experimental observation on the shape change of the prototype with temperature change agrees with the numerical simulation result. This shows that the numerical approach developed in this paper is capable of providing a reasonable prediction for the behavior of the proposed large bending actuator.