An enhanced model for shape memory alloy actuators with complex thermomechanical loadings

This paper presents an enhanced phenomenological model for shape memory alloy wires. Shape Memory Alloys (SMAs) are a group of materials with unique phase transformation related characteristics. They have been applied in both active and passive ways for actuation, vibration suppression, and sensing. SMA phenomenological models are widely used for engineering applications due to their simplicity and ease of simulation. A phenomenological model normally has two parts: a constitutive model based on free energy analysis and a phase transformation kinetics model based on experimental results. The existing phenomenological models are formulated to qualitatively predict the behavior of SMA systems for simple loadings. In this study, we have shown that there are certain situations in which these models are either not correctly formulated, and therefore are not able, to predict the behavior of SMA wires or the formulation is not straightforward for engineering applications. Such cases mostly happen when the temperature and the stress of the SMA wires change simultaneously. The phenomenological models discrepancy is studied experimentally using a dead-weight that is actuated by a SMA wire. An enhanced formulation is presented along with a modeling methodology for SMA systems with complex thermomechanical loadings.