Effect of strain rate on the macroscopic domain evolution in NiTi shape memory alloy strip under tension

Stress-induced phase transformations in polycrystalline NiTi SMA strips under uniaxial tensile loading are often accompanied by unstable mechanical behavior with formation and growth of localized deformation bands. These macroscopic deformation domains grow via the motion of the transformation fronts, the velocity of which is related to the external loading rate. The latent heat of transformation leads to significant thermo-mechanical coupling in both the stress-strain response of the material and the domain pattern itself. This paper reports recent experimental measurement on the evolution of domain patterns under different strain rates (10^-4/s, 10^-3/s and 10^-2/s). The results revealed a significant thermo-mechanical coupling in the behavior of the material, which demonstrates a strong effect of the applied nominal strain rate on the domain morphology and stress-strain curve. © 2009 SPIE