  There is little consensus on the nature of the glass state and its
relationship to other strain states in ferroelastic materials which show the
shape memory effect and superelasticity. We provide a thermodynamic
interpretation of the known strain states, including precursory tweed and
strain glass, by mapping the problem onto a spin model and analytically
obtaining the phase diagram using real-space renormalization group methods. We
further predict a spontaneous transition from the glass state to the ordered
martensite phase. We verify this prediction by mapping out the experimental
phase diagram for the ternary ferroelastic alloy Ti$_{50}$(Pd$_{50-x}$Cr$_x$)
and demonstrate the emergence of the spontaneous transition. Our work thus
provides a consistent framework to understand the various experimental and
theoretical studies on the glassy behavior associated with ferroelastic
materials.
