Evaluation of structural influence on performance of shape memory alloy linear actuators by sharp phase front-based constitutive models

This paper analyzes and compares the predictions of two sharp phase-front based shape memory alloy (SMA) constitutive models – proposed by Abeyaratne and Knowles (R. Abeyaratne, J. Knowles, Journal of Mechanics and Physics of Solids 41 (1993) 541) and Bruno et al. (O. Bruno, P. Leo, F. Reitich, Phys. Rev. Lett. 74 (1995) 746–749) – in the context of an SMA linear actuator (an SMA rod or a wire) actuated electrically and subjected to spring-loaded boundary conditions at its ends. Both models are then used to analyze the performance – i.e., specific energy output and energy efficiency – of the SMA actuator. The computational modeling is done using a moving boundary finite element method (MBFEM)-based numerical approach proposed by Stoilov et al. (V. Stoilov, O. Iliev, A. Bhattacharyya, Computer Methods in Applied Mechanics and Engineering, accepted). It is seen that while both models produce somewhat differing predictions of the SMA response, the difference is not dramatic enough to prefer one model to another. Predictions of the SMA actuator performance indicate that there is an optimum spring stiffness at which the energy efficiency of the SMA actuator is at its maximum. This raises the possibility that when an SMA actuator is integrated into a structure, the passive components of the structure may play a key role in determining the optimum energy efficiency of the active structural component (the SMA actuator) during the activation of the structure.