Modeling of thin layer extensional thermoelectric SMA actuators

As a first step towards the design of a high frequency, high force, large strain shape memory alloy (SMA) actuator, we model, in this work a thermoelectrically cooled thin SMA layer extensional actuator. The SMA is subjected to cyclic phase transition between the martensitic and austenitic phases by alternate heating/cooling, achieved with the thermoelectric Peltier effect of a pair of P/N semiconductors. The effect of a variable actuating load and a constant load applied as boundary conditions, on the SMA actuator, are considered. The thermomechanical boundary value problem involves strongly coupled thermal and mechanical fields. The evolution equations for the held variables are integrated using the fourth-order Runge-Kutta method and the coupling between the fields is accounted for by implementing an iterative scheme. The primary parameters of interest in this work are the frequency response and evolution of the variable load. The performance of the actuator is compared with various commercially available actuators based on energy conversion efficiencies and energy output per unit volume of active material. Results of the analysis indicate that thin SMA layers (approximate to 6 mu thick) under partial phase transformation are capable of delivering frequencies of about 30 Hz at peak stresses of about 145 MPa. (C) 1997 Elsevier Science Ltd.