Effects of Temperature Boundary Conditions on SMA Actuator Performance Using a Fully Coupled Thermomechanical Model

The effects of temperature boundary conditions and the resulting performance of an SMA actuator were studied for an SMA wire coupled with a stiff spring. The wire was actuated via joule heating under both adiabatic and isothermal boundary conditions. The resulting temperature, phase fraction, strain and stress profiles along the wire were studied together with the wire tip displacement. The simulations were conducted using the finite element program ABAQUS, and a fully thermo-mechanically coupled shape memory alloy (SMA) actuator model was used to simulate the behavior. ABAQUS’s user material (UMAT) feature was utilized to model the SMA wire using a mesoscopic free energy model [1] in order to accurately describe the thermomechanically coupled actuator behavior. The results from the simulations highlighted the differences between homogeneous and inhomogeneous profiles, and a 34% difference in actuation stroke between the two cases was observed.