Synergistic size-temperature effects on the transition of compression instability modes in shape memory alloy nanorods

Size effect is typically expected to play an important role in the performance of low-dimensional materials. Meanwhile, due to thermo-mechanical coupling in shape memory alloys (SMAs), temperature also significantly influences phase transformation. This study investigates the synergistic size-temperature effects on the compression instability of NiTi SMA nanorods (NRs) through molecular dynamics simulations and theoretical modeling. The results indicate that the observed instability modes in NRs, namely phase transformation and buckling, are predominantly determined by their length-to-diameter ratio (α). The critical α for the transition between these two instability modes is dictated by a competitive mechanism involving phase transformation driving stress and buckling stress, both of which depend on the size and temperature of the system. A modified Timoshenko model is developed to theoretically predict the critical α based on this stress competition mechanism, providing a comprehensive understanding of the synergistic size-temperature effects on the modulation of the critical α. These findings could offer valuable insights for the mechanical design and application of micro/nano devices utilizing SMA NRs.