  In the experiments on stress-induced phase transitions in SMA strips, several
interesting instability phenomena have been observed, including a necking-type
instability, a shear-type instability and an orientation instability. By using
the smallness of the maximum strain, the thickness and width of the strip, we
use a methodology, which combines series expansions and asymptotic expansions,
to derive the asymptotic normal form equations, which can yield the
leading-order behavior of the original three-dimensional field equations. Our
analytical results reveal that the inclination of the phase front is a
phenomenon of localization-induced buckling (or phase-transition-induced
buckling as the localization is caused by the phase transition). Due to the
similarities between the development of the Luders band in a mild steel and the
stress-induced transformations in a SMA, the present results give a strong
analytical evidence that the former is also caused by macroscopic effects
instead of microscopic effects. Our analytical results also reveal more
explicitly the important roles played by the geometrical parameters.
