Characterization and modeling of a shape memory allow actuated biomimetic vehicle

Abstract

The development of a biomimetic active hydrofoil that utilizes Shape Memory Alloy (SMA) actuator technology is presented herein. This work is the first stage prototype of a vehicle that will consist of many actuated body segments. The current work describes the design, modeling, and testing of a single segment demonstration SMA actuated hydrofoil. The SMA actuation elements are two sets of thin wires on either side of an elastomeric component that joins together the leading and trailing edges of the hydrofoil. Controlled heating and cooling of the two wire sets generates bi-directional bending of the elastomer, which in turn deflects the trailing edge of the hydrofoil. In this paper the design of the hydrofoil and the experimental tests performed thereon are explained. A detailed account of SMA actuator preparation (training) and material characterization is given. The constitutive model used for the SMA actuators is summarized and a parametric study of the material parameters used in this model is presented. Finite element method (FEM) modeling of hydrofoil response to electrical heating of the SMA actuators is carried out using a photomechanical constitutive model for SMA with input from the material characterization. The modeling predictions are finally compared with experimental measurements of the trailing edge deflection and the SMA actuator temperature. A scheme whereby the coupling of the hydrodynamic load and the hydrofoil shape is discussed. A verification of the scheme is given, as well as, a study of its convergence characteristics. The scheme is then used in FEM calculations to determine the effect of the hydrodynamic loads on the hydrofoil during an actuation cycle.