T. Georges, D. Coutu, V. Brailovski, P. Terriault, Ecole de technologie superieure, Montreal, QC, Canada
SMA actuators can effectively be used as active elements coupled with passive elastic structure of a morphing wing given their exceptional power density characteristics. Upon heating, SMA deforms the elastic envelope of the wing, while during cooling it is the elastic structure of the wing that restores the energy accumulated during actuation period, thus ensuring the SMA actuators resetting. The shape-changing behaviour of the morphing structure depends on a series of parameters which can be grouped as follows: the SMA characteristics, the elastic structure properties and the assembly conditions between active and passive subsystems. For a given elastic envelope designed to keep its structural integrity despite aerodynamic pressure variations, there are SMA characteristics and assembly conditions, which have to be adequately selected to optimize the performance of the whole morphing wing. For an SMA of a given composition, its recovery stress-strain characteristics are determined by the alloy’s thermomechanical history. The latter contains two periods: (a) prior-to-service period when the material is thermomechanically processed to obtain necessary properties and shape and (b) service period when the material repetitive heating and cooling results in a degradation of its force-generation properties (fatigue). This paper focuses on the development of the design methodology leading to the optimum selection of the thermomechanical treatment of SMA active elements and their assembly conditions with the elastic structure, according to the requirements imposed by the application as far as it concerns the necessary force-displacement characteristics and number of cycles of functioning. A case study of a minimum-weight optimisation is presented and the obtained results are experimentally validated.
Summary: This paper focuses on the development of the design methodology leading to the optimum selection of the thermomechanical treatment and assembly conditions for the SMA linear actuators intended to be used in morphing wing structures. A case study of a minimum-weight optimisation is presented and the obtained results are experimentally validated.
