Dynamic thermo-mechanical properties of shape memory alloy nanowires upon multi-axial loading

Dhote, R. P., Melnik, R. V. N., Zu, J. W.

Proceedings of the ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS-2011), Sept 18 - 21, 2011, Scottsdale, AZ, USA, Volume 2, Paper SMASIS2011-5210, pp. 411--417, ISBN 978-0-7918-5472-3, 2011


In this paper, we study the behavior of shape memory alloy (SMA) nanowires subjected to multi-axial loading. We use the model developed in our earlier work to study the microstructure and mechanical properties of finite length nanowires. The phase field model with the Ginzburg-Landau free energy is used to model the phase transformation based on the chosen order parameter. The governing equations of the thermo-mechanical model are solved simultaneously for different loading cases. We observe that nanowire behaves in a stiff manner to axial load with complete conversion of the unfavorable martensite to the favorable one. The bending load aids the phase transformation by redistributing the martensitic variants based on the local axial stress sign. The nanowire behavior to multi-axial (axial and bending together) is stiffer axially than the axial loading case. The understanding of the behavior of nanowire to multi-axial loading will be useful in developing better SMA-based MEMS and NEMS devices.

Keywords: dynamic problems, shape memory alloys, phaase transformations, multiaxial loading, MEMS and NEMS devices, nonlinear thermo-mechanical coupling, Ginzburg-Landau free energy, phase-field models