Exploration of the Partial Transformation Behaviour of Shape Memory Alloys and its Eu000bect on Actuation Performance

摘要

Multiple applications of shape memory alloys (SMA) involve operation under partial transformation (PT), wherereversal of the transformation direction takes place while the material is in a mixed phase state. Typicalapplications of SMAs include: actuators in adaptive/morphing structures which should repeatedly reach varioustarget shapes or to follow time trajectories at higher time rates; dampers vibrating pseudo-elastically undervarying amplitudes of dynamic loads. While the thermo-mechanically coupled behavior of SMAs under fulltransformation has been studied during the past and various models have been proposed, their response underPT has yet to receive the required attention to fully unravel the potential of these materials.In this paper, an experimental study of SMA wires under PT is presented along with a modied constitutivemodel. The physical constitutive model of Lagoudas et al.,1 is combined with a new expression of the hardeningfunction to enable the accurate and eu000ecient prediction of PT behaviour. The predicted PT response is correlatedwith isobaric, thermally induced PT cycle experiments. Very good agreement is obtained with measured partialcycles, especially for PT cycles formed near the middle of the major hysteresis loop.The new constitutive equations are included into a nite element framework to investigate the eu000bect of PTon SMA actuation function in morphing airfoils for active load alleviation in large wind turbine blades, andnumerical results are correlated with experimental data. The correlations prove the importance of PT behaviorin the actuator performance of SMAs, resulting in substantially more accurate predictions in deformation, stressand temperature.