**2. Experimental Observations**

Great progress has been made in uniaxial experiments to investigate the pseudo-elastic and yielding behaviors of NiTi SMAs under different strain rates. Shear and indentation tests have also been conducted, though less frequently compared to uniaxial. Experimental results under different loading rates have shown that the critical transformation stress increases as the strain rate grows. In addition to the loading mode, microstructure is another factor to influence the strain rate effect, which will be discussed at the end of this section.
