FE Analysis of SMA-Based Bio-Inspired Bone-Joint System

The application of shape memory alloys (SMA) as actuators in a smart structure is a quickly developing field. The particular focus of this paper is on the aspects of modeling and simulation of a bio-inspired bone-joint system using the finite element method (FEM). The actuation of a typical bat’s humerus-radius system is effected by means of micro-scale actuator wires performing like metal muscles when heated. In addition, the elbow is modeled as a flexible hinge using superelastic SMA wires. This system serves as a first step towards the design of a flapping wing to propel the next generation Micro Aerial Vehicle (MAV). In this bio-inspired bone-joint-system, the humerus and radius were modeled as standard elastic beams. Shape memory alloys were employed in two different ways: one is an SMA wire in the martensite phase, the other is an SMA beam in the austenite phase. The SMA wires work as muscles to actuate the bio-system due to contraction upon electric heating. The SMA beams work as flexible joints due to their superelastic character. In this work, the modeling and simulation of the adaptive structure was implemented in COMSOL Multiphysics. The active material model used is based on the Muller-Achenbach-Seelecke shape memory alloy model. The paper has a particular focus on the implementation of the SMA model into COMSOL combining general PDE modes with structural mechanics truss and beam elements. COMSOL has been chosen because of its natural way of handling multi-physics situations such as the thermomechanical coupling relevant for the SMA application.